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TADESSE, Tarekegn, Kazuhiro SUZUKI et Mitsuo HOSHINO. « Chemical Th-U-total Pb isochron age of zircon from the Mereb Granite in northern Ethiopia ». Dept. of Earth and Planetary Sciences, Nagoya University, 1997. http://hdl.handle.net/2237/2833.
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Sorota, Kristin Joy. « Age and Origin of the Merrimack Terrane, Southeastern New England : A Detrital Zircon U-Pb Geochronology Study ». Thesis, Boston College, 2013. http://hdl.handle.net/2345/3043.
Texte intégralRésumé :
Thesis advisor: J C. HepburnThesis advisor: Yvette D. Kuiper
Metasedimentary rocks of the Merrimack terrane (MT) originated as a thick cover sequence on Ganderia consisting of sandstones, calcareous sandstones, pelitic rocks and turbidites. In order to investigate the age, provenance and stratigraphic order of these rocks and correlations with adjoining terranes, detrital zircon suites from 7 formations across the MT along a NNE-trending transect from east-central Massachusetts to SE New Hampshire were analyzed by U-Pb LA-ICP-MS methods on 90-140 grains per sample. The youngest detrital zircons in the western units, the Worcester, Oakdale and Paxton Formations, are ca. 438 Ma while those in the Kittery, Eliot and Berwick Formations in the northeast are ca. 426 Ma. The Tower Hill Formation previously interpreted to form the easternmost unit of the MT in MA, has a distinctly different zircon distribution with its youngest zircon population in the Cambrian. All samples except for the Tower Hill Formation have detrital zircon age distributions with significant peaks in the mid-to late Ordovician, similar abundances of early Paleozoic and late Neoproterozoic zircons, significant input from ~1.0 to ~1.8 Ga sources and limited Archean grains. The similarities in zircon provenance suggest that all units across the terrane, except for the Tower Hill Formation, belong to a single sequence of rocks, with similar sources and with the units in the NE possibly being somewhat younger than those in east-central Massachusetts. The continuous zircon age distributions observed throughout the Mesoproterozoic and late Paleoproterozoic are consistent with an Amazonian source. All samples, except the Tower Hill Formation, show sedimentary input from both Ganderian and Laurentian sources and suggest that Laurentian input increases as the maximum depositional age decreases
Thesis (MS) — Boston College, 2013
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Geology and Geophysics
3
Loan, MaryEllen Louise. « New Constraints on the Age of Deposition and Provenance of the Metasedimentary Rocks in the Nashoba Terrane, SE New England ». Thesis, Boston College, 2011. http://hdl.handle.net/2345/2422.
Texte intégralRésumé :
Thesis advisor: J. Christopher HepburnThe Nashoba terrane of SE New England is one of three peri-Gondwanan tectonic blocks caught between Laurentia and Gondwana during the closure of the Iapetus Ocean in the early to mid- Paleozoic. U-Pb analyses (LA-ICP-MS) were carried out on zircon suites from the meta-sedimentary rocks of the Nashoba terrane. The youngest detrital zircons in the meta-sedimentary rocks of the Nashoba terrane are Ordovician in age. There is no significant difference in age between meta-sedimentary units of the Nashoba terrane across the Assabet River Fault Zone, a major fault zone that bisects the NT in a SE and a NW par. Zircon in meta-sedimentary rocks in the Marlboro Fm., the oldest unit of the Nashoba terrane, is rare, which may reflect the basaltic nature of the source material, and is commonly metamict. The Marlboro Fm. contained the oldest detrital grain of all the analyzed samples, with a core of ~3.3 Ga and rim of ~2.6 Ga indicating that it was sourced from Archaen crustal material. Detrital zircons from the Nashoba terrane show a complete age record between the Paleoproterozoic and Paleozoic that strongly supports a provenance from the Oaxiqua margin of Amazonia. The detrital zircon suite of the Nashoba terrane is distinct from both Avalonia and the Merrimack belt; however, they resemble zircon suites from Ganderia. This study proposes that the Nashoba terrane of Massachusetts correlates with the passive trailing edge of Ganderia. Finally, metamorphic zircon analyses of the terrane show that the Nashoba terrane experienced a peak in hydrothermal fluid infiltration during the Neoacadian orogeny
Thesis (MS) — Boston College, 2011
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences
4
Gärtner, Andreas. « Geologic evolution of the Adrar Souttouf Massif (Moroccan Sahara) and its significance for continental-scaled plate reconstructions since the Mid Neoproterozoic ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-234103.
Texte intégralRésumé :
Located in the south of the Moroccan Sahara, the Adrar Souttouf Massif is the northern continuation of the Mauritanides at the western margin of the West African Craton. The massif itself exhibits a complex polyphase geologic history and contains four geologically different, SSW-NNE trending main units named from west to east: Oued Togba, Sebkha Gezmayet, Dayet Lawda, Sebkha Matallah. They are thrusted over each other in thin-skinned nappes with local windows of the discordantly overlain Archaean Reguibat basement. The eastern margin of the massif is bordered by the Tiris and Tasiast-Tijirit areas of the Reguibat Shield as well as its (par-) autochthonous Palaeozoic cover sequence, termed Dhloat Ensour unit. More than 5.500 U-Th-Pb age determinations and over 1.000 Hf isotopic measurements on single zircon grains from igneous, metamorphic, and sedimentary rocks of all the massifs units and its vicinity have yet been obtained. Most of the zircons were studied with respect to their morphological features. This method improves the accuracy of provenance studies by detecting varying zircon morphologies in space and time. These data are accompanied by U-Th-Pb age determinations on apatite as well as rutile. Together, they allow proposing a model of the geologic evolution of this poorly mapped area for the last 635 Ma. A combination of the obtained data with extensive zircon age databases of the surrounding cratons and terranes facilitates continental-scaled palaeogeographic reconstructions.
Regarding the geologic evolution of the Adrar Souttouf Massif, the assembly of the first units began prior to 635 Ma. Although containing all the major zircon age and Hf-isotope populations of the West African Craton as well as some Mesoproterozoic grains, the Sebkha Gezmayet unit lies to the west of the Dayet Lawda unit of oceanic island arc composition. Hence, the Sebkha Gezmayet unit must have been rifted away from the craton prior to the formation of the oceanic unit within the West African Neoproterozoic Ocean at about 635 Ma. Recently published Hf and zircon age data of this unit suggest that the island arc was derived from a juvenile mantle source. Subsequently, the accretion of precursors of the Oued Togba and Sebkha Gezmayet units as well as a partial obduction of the oceanic Dayet Lawda unit and the Neoproterozoic sediments of a foreland basin (Sebkha Matallah unit) onto the Reguibat Shield took place. Peak metamorphism in the obducted oceanic rocks was reached at about 605 Ma. Magmatism in the western units between 610 and 570 Ma suggests on-going tectonic activity. The Early and Middle Cambrian is characterised by the erosion of the Ediacaran orogen and deposition of thick sedimentary sequences at the Sebkha Matallah unit, which acted as foreland basin. These sediments show a mostly West African zircon record with only some Mesoproterozoic grains provided by the westernmost parts of the massif. Initial rifting of the Oued Togba and Sebkha Gezmayet units from the remaining areas presumably occurred during the Late Cambrian. Coeval granitoid intrusions occurred on both sides of the rift. The two rifted units were likely involved to the polyphased Appalachian orogenies, which is emphasised by Devonian magmatism. Thus, and with respect to the isotopic data, the Oued Togba unit is interpreted to be of Avalonia affinity, while the Sebkha Gezmayet unit can likely be linked to Meguma. The units which remained at the West African Craton underwent intense sediment recycling during the entire Ordovician to Devonian times. Final accretion of all units and formation of the current massif was achieved during the Variscan-Alleghanian orogeny. This was accompanied by magmatism in the Sebkha Gezmayet unit and intense metamorphism of the Reguibat basement, whose zircons often show lower discordia intercepts of Carboniferous or Permian age. The post-Variscan period is characterised by erosion of the orogen and subjacent alternating cycles of sedimentation and deflation.
The Adrar Souttouf Massifs importance for palaeogeographic reconstructions is given by the striking differences in the zircon age and Hf-isotope record of its westernmost Oued Togba unit and the remaining area. The results obtained from the Oued Togba unit resemble the published data of the Avalonia type terranes including prominent Mesoproterozoic, Ediacaran-Early Cambrian, as well as Early Devonian age populations. Many Mesoproterozoic zircons, which are exotic for the West African Craton prior to 635 Ma, form a ca. 1.20 to 1.25 Ga age peak that is an excellent tracer for detrital provenance studies and source craton identification of the sedimentary rocks. This is also valid for some sedimentary samples that do not show ages younger than 700 Ma, but large quantities of Mesoproterozoic zircon. These rocks can be correlated to similar sediments in Mauritania and W-Avalonia and are thought to be of pre-pan-African", i.e. pre-Ediacaran or even pre-Cryogenian age. They may give direct insights to the source area in Early to Mid Neoproterozoic times. Accordingly, comparison with published data of Amazonia and Baltica, allows setting up new hypotheses for the pre-Ediacaran history of the Avalonian type terranes. Lacking of magmatism in Amazonia between ca. 1200 and ca. 1300 Ma favours Baltica as source craton for the Avalonian terranes and requires a new point of view for the Neoproterozoic palaeogeography.
5
Pepper, Martin Bailey. « Magmatic History and Crustal Genesis of South America : Constraints from U-Pb Ages and Hf Isotopes of Detrital Zircons in Modern Rivers ». Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/347220.
Texte intégralRésumé :
South America provides an outstanding laboratory for studies of magmatism and crustal evolution because it contains older Archean-Paleoproterozoic cratons that amalgamated during Mesoproterozoic and Neoproterozoic supercontinent assembly, as well as a long history of Andean magmatism that records crustal growth and reworking in an accretionary orogen. We have attempted to reconstruct the growth and evolution of South America through U-Pb geochronology and Hf isotope analyses of detrital zircons from 59 samples of sand from modern rivers and shorelines. Results from 5,524 new U-Pb ages and 1,199 new Hf isotope determinations are reported. We have also integrated our data into a compilation of all previously published zircon geochronologic and Hf isotopic information, yielding a record that includes>42,000 ages and>1,600 Hf isotope analyses. These data yield five main conclusions: (1) South America has an age distribution that is similar to most other continents, presumably reflecting the supercontinent cycle, with maxima at 2.2-1.8 Ga, 1.6-0.9 Ga, 700-400 Ma, and 360-200 Ma; (2)<200 Ma magmatism along the western margin of South America has age maxima at 183 Ma (191-175 Ma), 151 Ma (159-143 Ma), 126 Ma (131-121 Ma), 109 Ma (114-105 Ma), 87 Ma (95-79 Ma), 62 Ma (71-53 Ma), 39 Ma (43-35 Ma), 19 Ma (23-15 Ma), and 6 Ma (10-2 Ma); (3) for the past 200 Ma, there appears to be a positive correlation between magmatism and the velocity of convergence between central South America and Pacific oceanic plates; (4) Hf isotopes record reworking of older crustal materials during most time periods, with incorporation of juvenile crustal materials at ~1.6-1.0 Ga, 500-400 Ma and ~200-100 Ma; and (5) the Hf isotopic signature of<200 Ma magmatism is apparently controlled by the generation of juvenile magmas during extensional tectonism and reworking of juvenile versus evolved crustal materials during crustal thickening and arc migration.
6
Luo, Yan. « U-Pb age and Hf isotopic study of detrital zircons from the Liaohe Group constraints on the evolution of the Jiao-Liao-Ji Belt, North China craton / ». Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36639242.
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Wilson, John Robert. « U/Pb Zircon Ages of Plutons from the Central Appalachians and GIS-Based Assessment of Plutons with Comments on Their Regional Tectonic Significance ». Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/35248.
Texte intégralRésumé :
The rocks of the Appalachian orogen are world-class examples of collisional and extensional tectonics, where multiple episodes of mountain building and rifting from the pre-Cambrian to the present are preserved in the geologic record. These orogenic events produced plutonic rocks, which can be used as probes of the thermal state of the source region. SIMS (secondary ion mass spectrometry) U/Pb ages of zircons were obtained for ten plutons (Leatherwood, Rich Acres, Melrose, Buckingham, Diana Mills, Columbia, Poore Creek, Green Springs, Lahore and Ellisville) within Virginia. These plutons are distinct chemically, isotopically, and show an age distribution where felsic rocks are approximately 440 Ma, and Mafic rocks are approximately 430 Ma. Initial strontium isotopic ratios and bulk geochemical analyses were also performed. These analyses show the bimodal nature of magmatism within this region.
In order to facilitate management of geologic data, including radiometric ages, strontium isotope initial ratios and major element geochemistry, a GIS based approach has been developed. Geospatially references sample locations, and associated attribute data allow for analysis of the data, and an assessment of the accuracy of field locations of plutons at both regional and local scales. The GIS based assessment of plutons also allows for the incorporation of other multidisciplinary databases to enhance analysis of regional and local geologic processes. Extending such coverage to the central Appalachians (distribution of lithotectonic belts, plutons, and their ages and compositions) will enable a rapid assessment of tectonic models.Master of Science
8
Sakata, Shuhei. « Development of analytical technique for precise age determination of Quaternary zircons with the correction of the initial disequilibrium on U-Th-Pb decay series using a laser ablation-ICP-mass spectrometry ». 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199112.
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Gruber, Leonardo. « Geocronologia U-Pb em Zircão Detrítico aplicada ao estudo de proveniência de metassedimentos do Complexo Metamórfico Porongos – Região de Santana da Boa Vista, RS ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/56342.
Texte intégralRésumé :
Estudos de proveniência em zircões detríticos através do método U-Th-Pb (LA-ICP-MS) dos metassedimentos do Complexo Metamórfico Porongos determinaram a existência de duas áreas-fontes principais de onde derivaram idades paleoproterozóicas e mesoproterozóicas para os xistos Arroio Areião, Cerro Cambará e quartzo milonitos associados. Foram obtidas idades entre 967 ± 15 Ma e 2454 ±26 Ma para a seqüência Arroio Areião, entre 894 ± 30 Ma e 2783 ± 18 Ma para a seqüência Cerro Cambará, e idades entre 1621 ± 16 Ma e 3185 ± 117 Ma para os quartzo milonitos associados. A área fonte com idades paleoproterozóicas pode ser correlacionada ás rochas do Complexo Encantadas, que faz parte do embasamento das unidades supracrustrais. As áreas-fontes para os zircões mesoproterozóicos (entre 967 e 1621 Ma) não foram ainda reconhecidas no Cinturão Dom Feliciano. Estes zircões podem ser derivados de associações de rocha pertencentes aos cinturões mesoproterozóicos (orogêneses Elzeverian e Greenville), associados ao sistema geodinâmico que incluí os crátons Amazonas, Kalahari, Congo – São Francisco e Laurencia e cinturões associados. O ambiente geotectônico de formação da paleobacia Porongos é compatível com a margem passiva, onde se estabeleceu um arco magmático. Este trabalho demonstra que do ponto de vista isotópico e estratigráfico, não existem diferenças significativas de idades detríticas entre as seqüências metassedimentares que afloram nos flancos da Antiforme de Santana da Boa Vista.Provenance studies based upon detritic zircon grain U-Th-Pb methodology (LA-ICP-MS) from metasediments of Porongos Metamorphic Complex have determined the existence of two principal source-areas with paleoproterozoic and mesoproterozoic ages to the schists of Arroio Areião, Cerro Cambará and associated quartz mylonites. Where obtained ages between 967 ± 15 Ma and 2454 ±26 Ma to the Arroio Areião sequence, between 894 ± 30 Ma and 2783 ± 18 Ma to Cerro Cambará sequence, and 1621 ± 16 Ma e 3185 ± 117 Ma to the associated quartz mylonites. The source-area with paleoproterozoic ages can be related to the Encantadas Complex rocks, which is basement of the supracrustal sequences. The source-areas to the mesoproterozoic zircons (between 967 and 1621 Ma) are not recognized in the Dom Feliciano Belt. These zircons can be related to mesoproterozoic petrotectonic associations (Greenville and Elzeverian orogens) associated to the geodynamic system that includes the Amazon, Kalahari, Congo – São Francisco and Laurentia cratons, and associated belts. The tectonic environment of Porongos paleobasin it’s compatible with a passive margin, after where established a magmatic arc environment. This work shows that from isotopic and stratigraphyc point of view there is no significantly differences between the metasedimentary sequences cropping out in both Santana da Boa Vista antiform flanks.
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Luo, Yan, et 羅彥. « U-Pb age and Hf isotopic study of detrital zircons from the Liaohe Group : constraints on the evolution of theJiao-Liao-Ji Belt, North China craton ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36639242.
Texte intégral
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Yihunie, Tadesse. « Chemical Th-U-total Pb isochron ages of zircon and monazite from granitic rocks of the Negele area, southern Ethiopia ». Dept. of Earth and Planetary Sciences, Nagoya University, 2003. http://hdl.handle.net/2237/7624.
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Zeng, Wen. « The evolution of the metamorphic series in the NW Fujian Province, the NE Cathaysia Block, and the significance in the reconstruction of Precambrian Supercontinents ». Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/1091.
Texte intégralRésumé :
This thesis focuses on the Paleoproterozoic to Late Paleozoic basement evolution of the metamorphic rocks scattered in the NW Fujian Province, the NE Cathaysia Block the southeastern area of South China. Field observation, systematic sampling and petrographic investigation combined with of whole rock geochemistry, zircon U-Pb, Lu-Hf isotopes, trace elements, amphibole and biotite 40Ar/39Ar analyses and mineral chemistry study were applied in this project to determine the nature, ages and relations of the leucosomes, felsic paragneiss and mafic metamorphic rocks in study area and their implications to the reconstruction of the Precambrian Rodina Supercontinent.Following conclusions are made: 1. Based on this study, according to their metamorphism and deformation characteristics, the metamorphic rock series in the study area can be divided into two types, moderately to strongly metamorphosed rock series that experienced ductile deformation and moderately metamorphosed rock series that have experienced ductile deformations. New La-ICPMS U-Pb zircon ages presented here and in previous study suggest that the original lithostratigraphy should be abandoned and the terminology “Complex” should be used instead of “Group” and “Formation” for the high grade metamorphic rock series in northwestern Fujian, where the protoliths were strongly reworked by Early Paleozoic tectono-thermal events.2. Obvious zircon U-Pb age peaks of ~1800 Ma suggest that the protoliths ofthe Cathaysia Block be comparable to the basements of North America ratherthan those of Eastern India and East Antarctica. Although the peaks of ~1800Ma are also present in Western Australia, their 176Hf/177Hf ratios (0.280706 -0.281510) are apparently lower than those of zircons from SW Cathaysia (0.281515 - 0.282098) and from this study (0.281232 - 0.282213, NECathaysia). Besides, detrital zircons in Cathaysia and NW Yangtze indicatesignificant juvenile input during Paleo- to Mesoproterozoic according to thezircon Hf isotopes, which are distinctly different from Western Australia.These evidences suggest that the basement of the Cathaysia share similaritieswith that of North America, lending support for the Rodinia configurationproposed by Li et al. (2008), in which Cathaysia was next to western Laurentia before and during the late Mesoproterozoic assembly of Rodinia.2. Obvious zircon U-Pb age peaks of ~1800 Ma suggest that the protoliths of the Cathaysia Block be comparable to the basements of North America rather than those of Eastern India and East Antarctica. Although the peaks of ~1800 Ma are also present in Western Australia, their 176Hf/177Hf ratios (0.280706 - 0.281510) are apparently lower than those of zircons from SW Cathaysia (0.281515 - 0.282098) and from this study (0.281232 - 0.282213, NE Cathaysia). Besides, detrital zircons in Cathaysia and NW Yangtze indicate significant juvenile input during Paleo- to Mesoproterozoic according to the zircon Hf isotopes, which are distinctly different from Western Australia. These evidences suggest that the basement of the Cathaysia share similarities with that of North America, lending support for the Rodinia configuration proposed by Li et al. (2008), in which Cathaysia was next to western Laurentia before and during the late Mesoproterozoic assembly of Rodinia.3. The protoliths of the felsic paragneiss in the NW Fujian area are immaturesediments, consisting of greywacke, arkose and lithic arenite compositions.The significant input of the paragneiss protolith was dominantly formed byseveral magmatic events during Neoproterozoic (820 ± 6 Ma, 780 ± 6 Ma, 776± 6 Ma, 758 ± 3 Ma, 740 ± 8 Ma and 722 ± 9 Ma), probably deposited notearly than middle Neoproterozoic (~680 Ma). Many metamorphic rockscontain 0.99 - 0.72 Ga detrital magmatic zircons, which are interpreted asreflecting the tectono-thermal events related to the assembly and break-up of the Rodinia supercontinent during the Neoproterozoic.4. In this study, new La-ICPMS U-Pb anatectic zircon data from the NWFujian area suggest that the strong and widespread tectono-thermal eventswere related to the orogeny probably having started during the MiddleCambrian and lasted until the Middle Devonian, consisting of at least threemain episodes (~473 Ma, ~445 Ma, ~423 Ma), with major orogeny events(including syn- to post-orogenic melting) constrained between ~473 Ma and~407 Ma in the NE Cathaysia, and between ~468 Ma and ~415 Ma in the SWCathaysia. The age peaks in the Cathaysia Block (ca. 488, 471, 455, 440 and415 Ma) are within the age range of the Qinling-Tongbai-Dabie orogen during 512 - 406 Ma. This suggests a possible linkage or interaction of the two orogens.5. The duration of the “Caledonian” orogeny in the NW Fujian area was noshorter than ~50 Myr, starting at ~473 Ma (~Early Ordovician) or earlier, andterminating at ~423 Ma (~Middle Silurian) or later. The “Caledonian”orogenic event in the Cathaysia Block was likely due to an intracontinentalcollision rather than the subduction of oceanic crust or arc-continentalcollision. Considering the inhomogeneous cooling paths for the Tianjingping,the Jiaoxi and Mayuan complexes, and different time restraint of thewidespread anatectic and magmatic events occurred in different places, the“Caledonian” tectono-thermal events in the Cathaysia Block might vary between different segments of the orogen.
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Perkes, Tyson L. « Integrating Facies Analysis, Terrestrial Sequence Stratigraphy, and the First Detrital Zircon (U-Pb) Ages of the Twist Gulch Formation, Utah, USA : Constraining Paleogeography and Chronostratigraphy ». Diss., CLICK HERE for online access, 2010. http://contentdm.lib.byu.edu/ETD/image/etd3409.pdf.
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Liu, Chaohui, et 刘超辉. « Paleoproterozoic basins in the Trans-North China Orogen : stratigraphic sequences, U-PB ages and HF isotopes of detritalzircons and tectonic implications ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47163902.
Texte intégralRésumé :
The Trans-North China Orogen (TNCO) has been recognized as a continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form the North China Craton. However, controversy has surrounded the timing and tectonic processes involved in the collision between the two blocks, ranging from the westward-directed subduction with final collision at ~2.5 Ga, through the west-dipping subduction with two collisional events at ~2.1 Ga and ~1.85 Ga, to the eastward-directed subduction with final collision at ~1.85 Ga. This project aims to present detailed lithostratigraphic, geochronological and isotopic data for the low-grade supracrustal successions in the TNCO to examine current models and to establish a reasonable scenario for the tectonic evolution of the TNCO in the Paleoproterozoic.
The low-grade supracrustal successions include the Hutuo and Yejishan Groups in the middle sector of the TNCO and the Songjiashan, Lower Zhongtiao, Upper Zhongtiao, Danshanshi and Songshan Groups in the southern sector. Lithostratigraphic data indicate that the Songjiashan, Lower Zhongtiao Groups and lower parts of the Hutuo and Yejishan Groups are composed of metaclastic rocks, carbonates and metavolcanic rocks, interpreted as back-arc basin deposits, whereas the Upper Zhongtiao, Danshanshi, Songshan Groups and the upper parts of the Hutuo and Yejishan Groups consist only of metaconglomerates and metasandstones, interpreted as foreland basin deposits.
To constrain the provenance and maximum depositional ages for these low-grade supracrustal successions, the LA-MC-ICP-MS technique was applied to analyze U-Pb and Hf isotopic compositions for detrital zircons from them. For the Hutuo and Yejishan Groups, we found major age peaks at ~2.5 and ~2.2 Ga and minor amounts of 2.8-2.6 Ga detrital zircons, which are consistent with ages of the lithological units in the middle sector of the TNCO. On the other hand, for the Songjiashan, Lower Zhongtiao, Upper Zhongtiao, Danshanshi and Songshan Groups, detrital zircons from them have the major age population of 2.85-1.95 Ma and the minor age population of 3.6-3.1 Ga, of which the former is comparable with ages of the lithological units in the southern sector of the TNCO and the latter was derived from the Paleoarchean and Mesoarchean crust of the Eastern Block. The maximum depositional ages of the low-grade supracrustal successions have also been well constrained in this study. For the back-arc basin deposits, their maximum depositional ages were constrained between ~2.15 and ~2.10 Ga. For the foreland basin deposits, the presence of ~1.85 Ga detrital zircons indicates that they were deposited after this time.
Taken together, we present a brief scenario for the evolution of the sedimentary basins in the TNCO. At 2.15-2.10 Ga, a series of back-arc basins developed behind an “Andean-type” arc that were subsequently incorporated into the TNCO during the collision of the Eastern and Western Blocks. At ~1.85 Ga, the two blocks collided along the TNCO, resulting in the crustal thickening followed by rapid exhumation/uplift, which shifted the back-arc basins to foreland basins. Such a shift in the late Paleoproterozoic supports the model that the collision between the Eastern and Western Blocks occurred at ~1.85 Ga.published_or_final_version
Earth Sciences
Doctoral
Doctor of Philosophy
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LIMONCELLI, MARTA. « Short-term erosion pattern in the Alps-Apennines belt constrained by downstream changes of zircons morphology and U-PB ages from the Po drainage modern sands ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2012. http://hdl.handle.net/10281/29393.
Texte intégralRésumé :
Downstream changes of the geochronological signature in the Po drainage allow to assess the relative sediment contributions shed from the orogenic source areas, in order to constrain the short-term (102-104 y) erosion pattern in the Alps-Apennines orogenic couple.
In this perspective, we collected modern sands in selected tributaries draining the major tectonic units exposed in the orogen, as well as along the Po River trunk and in different sites of the Po Delta. Zircon concentrates were separated according to specific quantitative procedures coupled with grain-size and grain-density analyses, which provide an evaluation of zircon content in source rocks, of hydraulic sorting effects, and related intersample/intrasample zircon variability. Our methodological approach allows to perform sediment budgets and evaluate mineral content in diverse sediment sources (mineral fertility). Budget calculations were performed by investigating geochronological signals upstream and downstream of major confluences. We employed, LA-ICPMS U-Pb geochronology on detrital zircons, because this technique allows a full control of zircon populations during separation procedures and data analysis; we found, instead, that fission track dating on detrital zircon is affected and biased by selective grain loss.
Results of U-Pb analysis performed on single grains show that all samples from the Po Delta yield similar grain-age distributions, and include grain-age populations that are rather constant both in age and size. Major peaks are found at ca. 30 Ma, ca. 280 Ma, and 400-500 Ma. Peaks in these distributions can be traced upstream up to their sources. The bulk of the geochronological signature of the Po Delta sands is displayed already upstream of the confluence of the Northern Apennines rivers, suggesting that short-term erosion rates were much lower in the Northern Apennine than in the Western and Central Alps. Age peaks typical of the eastern Lepontine dome also characterize the Apenninic tributaries, reflecting Oligo-Miocene sedimentary transfer from the Central Alps to the Adriatic foredeep, and next tectonic accretion of turbidite wedges to the Apennine belt.
U-Pb analyses were complemented by zircon typology of the whole dataset, integrated by SEM observations on selected samples. Major typological groups can be traced from entry points in the Po Plain down to the Po Delta. Euhedral zircons are largely shed from the External Massifs (Mont Blanc and Argentera) and the Periadriatic plutons. Zircon grains showing signs of chemical abrasion, possibly acquired under high-grade metamorphic conditions, were detected in tributaries draining the Lepontine area.
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D'ADDA, PAOLO. « Eo-alpine evolution of the central southern alps. Insights from structural analysis and new geochronological constraints ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2011. http://hdl.handle.net/10281/19018.
Texte intégralRésumé :
The timing of the Alpine deformation in the Central Southern Alps (CSA or Orobic Alps) has always been a debated topic, since the scarcity of reliable absolute age constraints has prevented an accurate chronological reconstruction of the evolution of this sector of the European Alps.
In this work, detailed structural analyses performed in different areas of the CSA allowed us to distinguish different compressive features within both the crystalline basement and the sedimentary cover. The integration of these field data with new isotopic data provides time constraints for the reconstruction of the evolution of the CSA during the Alpine orogeny.
In the northern sector of the belt a Variscan polymetamorphic basement is stacked southward on the Permian to Mesozoic cover along two main regional faults (Orobic and Porcile thrusts). Fault zones, slightly postdating a first folding event of Alpine age (D3), experienced a complex evolution through the ductile and brittle deformation regime, showing greenschists facies mylonites overprinted by a penetrative cataclastic deformation (D4). Generation of fault-related pseudotachylytes marks the onset of brittle conditions, lasting up to the youngest episodes of fault activity.
Thrusting along this structures also produced thrusting within the Permian-Triassic cover with the formation of different south-verging thrust stacks. This first thrusting event was followed by the activation of new deeper thrust surfaces leading to the emplacement of three regional anticlines (Orobic Anticlines) which tilted to the south the previously stacked units. During this long compressive stage (Orobic-Porcile thrusts and Orobic Anticlines) the sedimentary cover of the CSA was also involved in thrusting and different stacks of Mesozoic units were emplaced to the south. 40Ar/39Ar dating of the pseudotachylyte matrix of 9 samples from both the Orobic and Porcile thrusts give two separated age clusters: Late Cretaceous (80-68 Ma) and Early to Middle Eocene (55-43 Ma). These new data provide evidence that the pre-Adamello evolution of the CSA was characterized by the superposition of different tectonic events accompanying the exhumation of the deepest part of the belt through the brittle-ductile transition. The oldest pseudotachylyte ages demonstrate that south-verging regional thrusting in the CSA was already active during the Late Cretaceous, concurrently with both the HP metamorphism that affected the Austroalpine units of the eastern Alps, and the development of a syn-orogenic foredeep basin where the Upper Cretaceous Lombardian Flysch was deposited.
In the Early to Middle Eocene a minor reactivation of the Orobic and Porcile thrusts occurred, as testified by the youngest pseudotachylyte ages obtained by 40Ar/39Ar dating. This event was probably related with the closure of the Ligurian-Piedmont and the ongoing of the Europe-Adria collision.
South of the Orobic Anticlines system the Triassic sedimentary succession is stacked into several units bounded by south-verging low-angle thrust faults, which are related to different steps of crustal shortening. Different thrust stacks occur within the Triassic cover between the Como Lake to the west and the Adamello batholith to the east. They usually have an antiformal arrangement and are separated by each other by different N-S trending transverse zones, such as the poorly known Grem-Vedra Transverse Zone (GVTZ), formed during complex deformational phenomena in a transpressional regime coeval with thrust emplacement. The GVTZ formed during the southward imbrication of the older thrust sheets of the Menna-Arera group, strongly interacting with syn-thrust ductile structures, and was reactivated during the growth of the Orobic Anticlines belt. The GVTZ and other transverse zones of the CSA probably reflect the occurrence of pre-existing fault systems that characterize the Norian to Jurassic rifting history of the Lombardian basin, and were reactivated as strike-slip features during Alpine tectonics.
In the Gandino and Presolana areas thrust surfaces are cut by high-angle extensional and strike-slip faults, which controlled the emplacement of hypabissal magmatic intrusions that post-date thrusts motions. Intrusion ages based on SHRIMP U-Th-Pb zircon dating span between 42±1 and 39±1 Ma, suggesting close time relationships with the earliest Adamello intrusion stages and, more in general, with the widespread calc-alkaline magmatism described in the Southern Alps. Fission track ages of magmatic apatites are indistinguishable from U-Pb crystallization ages of zircons, suggesting that the intrusion occurred in country rocks already exhumed above the partial annealing zone of apatite (depth < 2-4 km).
These data indicate that the northern and central sectors of the CSA were already structured and largely exhumed in the Middle Eocene and no major internal deformations has occurred in these areas after the Bartonian. Neogene deformations were instead concentrated further south, along the frontal part of the belt (Milano Belt).
These new data provide a direct evidence that thrusting and nappe stacking were active during Late Cretaceous times not only in the Eastern Alps, but also in the CSA, significantly extending southward the sector of the Alpine belt affected by the Cretaceous orogenic event. In this view, the Late Cretaceous Southern Alps can be interpreted as the south-verging retrobelt of a pre-collisional orogenic wedge, which formed during the subduction of the Alpine Tethys beneath the attenuated northern Adria margin.
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Barbeau, David Longfellow Jr. « Application of Growth Strata and Detrital-Zircon Geochronology to Stratigraphic Architecture and Kinematic History ». Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/244092.
Texte intégralRésumé :
Growth strata analysis and detrital-zircon geochronology are useful applications of stratigraphy to tectonic problems. Whereas both tools can contribute to kinematic analyses of supracrustal rock bodies, growth strata are also useful for analyzing the influence of tectonics on stratigraphic architecture. This study reports: 1) a conceptual model for growth strata development; 2) stratigraphic and kinematic analyses of growth strata architectures from growth structures in southeastern Utah, the Gulf of Mexico, and northeastern Spain; and 3) the detrital-zircon geochronology of the Salinian block of central coastal California. Kinematic sequence stratigraphy subdivides growth strata into kinematic sequences that are separated by kinematic sequence boundaries. Kinematic sequences can be further partitioned into kinematic domains based on the termination patterns of strata within a kinematic sequence. Salt- related fluvial growth strata from the Gulf of Mexico and southeastern Utah contain stratigraphic architectures that are unique to different kinematic domains. Offlap kinematic domains contain fluvial strata indicative of high slopes, low accommodation rates, and strong structural influence on paleocurrent direction. Onlap kinematic domains contain fluvial strata indicative of moderate slopes, high accommodation rates, and decreased structural influence on paleocurrent direction. The stratigraphic architecture of alluvial -fan thrust -belt growth strata in northeastern Spain does not display a marked correlation with kinematic domain, and is most easily interpreted using existing models for autocyclic alluvial -fan evolution. Detrital- zircon (U -Pb) geochronologic data from basement and cover rocks of Salinia suggest that Salinia originated along the southwestern margin of North America, likely in the vicinity of the Mojave Desert. The presence of Neoproterozoic and Late Archean detrital zircons in Salinian basement rocks also suggest that Salinian sediments were recycled from miogeoclinal sediments of the western margin of North America.
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Demouy, Sophie. « La naissance des Andes au Crétacé supérieur : origine et construction du Batholite côtier sud-péruvien (région d'Arequipa) ». Toulouse 3, 2012. http://thesesups.ups-tlse.fr/2201/.
Texte intégralRésumé :
Durant le Crétacé supérieur-Paléocène, une intense activité magmatique localisée le long de l'arc Toquepala a entraîné la création d'un relief important le long de la marge sud-péruvienne. La croissance de cet arc coïncide avec le seul soulèvement connu le long de la marge, ce qui permet de proposer qu'il en est un moteur principal. Notre étude se concentre sur une section du Batholite Côtier péruvien qui s'étend sur 80x60 km pour une épaisseur supérieure à 7 km. Les données structurales décrivent un objet complexe, constitué d'unités plutoniques dont certaines ont subi des épisodes de déformation extensive syn à post mise en place. De grandes failles normales structurent le batholite en réponse à des contraintes tectoniques et à la croissance exagérée de l'arc. L'étude géochronologique souligne la construction discontinue du batholite, au Jurassique (200-175 Ma) et au Crétacé-Paléocène (90-60 Ma). L'exploitation des données géochimiques et isotopiques (Hf, Sr, Nd) permet d'identifier un premier stade dans l'activité de l'arc, caractérisé par une prédominance des processus de mélange et de cristallisation fractionnée, et un second stade durant lequel les magmas homogénéisés évoluent seulement par cristallisation fractionnée pour se mettre en place au niveau du batholite sous la forme d'unités très volumineuses. La maturité du système s'exprime par un phénomène de flare-up entre 70-60 Ma durant lequel plus de 70% du batholite est mis en place. Ce phénomène de haut flux magmatique est caractérisé par des signatures juvéniles des magmas et constitue un apport non négligeable à la croûte continentaleDuring the Late Cretaceous and Paleocene, intense magmatic arc activity resulted in the building of a continuous relief along the Peruvian margin. This arc growth coincided with the only known significant uplift along the coastal southern Peru. Our study has focused in the Arequipa area, on a batholith segment extending 80x60 km for a thickness bigger than 7 km. The structural study describes an object that is complex and consists of different plutonic units, that for some underwent extensive deformation syn to post emplacement. Major faults affect the batholith as a consequence of tectonic strains and exaggerate growth of the arc. The geochronological study indicates a discontinuous construction of the batholith, during the Jurassic (200-175 Ma) and the Late Cretaceous-Paleocene (90-60 Ma). Exploitation of the geochemistry and isotopic data (Hf, Sr, Nd) allows to identify an initiation stage of the arc during which fractional crystallization and mixing are predominant, and a thermal maturation stage during which magmas are homogenized in the deep crust, and evolve by fractional crystallization until the batholith level. This period leads to the construction of more than 70 % of the batholith and can thus be considered as a flare-up event. This event is characterized by juvenile signatures and also contributes significantly to the growth of the continental crust
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Melleton, Jérémie. « Modalités du recyclage de la croûte continentale dans l'orogène varisque par traçage in situ des zircons hérités (mesures U -Pb/LA-MC-ICPMS) ». Phd thesis, Université d'Orléans, 2008. http://tel.archives-ouvertes.fr/tel-00388706.
Texte intégralRésumé :
Ce travail de thèse est essentiellement consacré à l'investigation des populations de zircons et de l'âge des protolithes des formations varisques grâce à une datation U-Pb in situ systématique par le couplage Laser/MC-ICPMS, dans des formations orthodérivées, métasédimentaires et magmatiques tardi-orogéniques du Massif Central français et du domaine Sud armoricain. Cette étude a montré que les populations de zircons sont largement héritées, s'étalant de l'Archéen au Paléozoïque inférieur. L'ensemble des pics d'âges obtenus, ainsi que l'absence d'âge mésoprotérozoïque (1.7-1.1 Ga) accréditent l'affinité gondwanienne de ces formations. Des âges maximum de dépôt sont proposés pour les métasédiments des principales unités définies dans le Massif Central. Ces âges maximum de dépôt sont décroissants suivant l'empilement lithotectonique reconnu. En marge de ce travail, nous avons pu déterminer que les âges de mise en place des granitoïdes du Sillon Houiller (Massif Central) et du golfe du Morbihan se situent aux alentours de 300 Ma. Des âges plus anciens, principalement obtenus sur monazite lors d'études antérieures, ont été réinterprétés comme des âges hérités. L'abondance de zircons hérités d'âge ordovicien et néoprotérozoïque met en évidence la large contribution des métagranites et métasédiments fertiles de ces périodes dans la source des granites tardi-orogéniques varisques. Le granite de Sarzeau expose de plus les traces d'un protolithe silurien. Le recyclage de la croûte continentale est caractérisé par une évolution polycyclique au cours de l'orogénèse varisque, avec tout d'abord l'érosion de formations du craton africain, majoritairement d'âge néoprotérozoïque, puis la superposition des événements magmatiques cambro-ordoviciens et syn-orogéniques varisques.
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Guerin, Gwénaël. « Contraintes cinématiques et thermiques de l'évolution des "metamorphic core complexes" du SE Arizona (Santa Catalina-Rincon) ». Rennes 1, 1988. http://www.theses.fr/1988REN10130.
Texte intégralRésumé :
Ces domes metamorphiques de la province bassin and range sont significatifs de la deformation de la croute ductile pendant l'extension tertiaire et de nombreux modeles d'extension intracontinentale furent proposes. Il est demontre la presence d'un epaississement important ante-extension lie a l'orogenese sevier laramienne, il apparait donc que les modalites d'extension risquent d'etre controlees par l'evenement compressif. Cette etude structurale a permis de differencier 3 deformations ductiles, et des datations u-pb sur zircon ont permis de reconstituer la chronologie des evenements. Une compilation des donnees geochronologiques retrace l'evolution temperature-temps
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Neace, Erika R. « Zircon LA-ICPMS Geochronology of the Cornubian Batholith, SW England ». Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1448912006.
Texte intégral
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Bootes, Nathaniel R. « Late Cenozoic Offshore Record of Exhumation and Sediment Routing in Southeast Alaska from Detrital Zircon U/Pb and FT double-dating ». University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1592169111121451.
Texte intégral
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Hund, Erik A. « U-Pb dating of granites from the Charlotte belt of the southern Appalachians ». Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45758.
Texte intégralRésumé :
New U-Pb zircon ages from plutons in the Charlotte belt of the southern Appalachians have provided evidence of Cambro-Ordovician and Siluro-Devonian magmatic activity. Several U-Pb zircon ages of Cambro-Ordovician plutons predate their Rb-Sr whole rock ages by as much as 60 m.y., suggesting a post emplacement disturbance of the Rb-Sr isotopic systems. Comparison of geologic setting, chemistry, and temporal and spatial distribution of Charlotte belt Siluro-Devonian plutons with those of other tectonic environments, specifically plutons from tensional environments, suggests a model for strike-slip accretion.Master of Science
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Martin, Laure. « Signification des âges U-Pb sur zircon dans l'histoire métamorphique de Naxos et Ikaria (Cyclades, Grèce) ». Nancy 1, 2004. http://www.theses.fr/2004NAN10231.
Texte intégralRésumé :
La compréhension de l'évolution des chaînes de montagnes nécessite la reconstruction des chemins pression-température-temps suivis par les roches métamorphiques. La datation U-Pb est souvent utilisée pour dater des événements métamorphiques, mais le lien entre les conditions du métamorphisme et l'âge fourni par les datations U-Pb sur zircon n'est pas direct. Les isotopes de l'oxygène sont proposés dans cette étude pour mettre en relation la croissance du zircon avec celle du grenat dans les roches métamorphiques du domaine égéen. L'étude de quatre échantillons de l'île de Naxos a montré que cette relation est possible si (i) l'équilibre isotopique de l'oxygène est atteint entre le grenat et le zircon au moment de leur formation et (ii) le grenat et le zircon sont restés clos pour l'oxygène et le plomb après leur formation. Cette méthode a permis de dater le début de l'exhumation des roches métamorphiques de Naxos entre 40 et 60 Ma, et le début du chemin rétrograde entre 13 et 19 Ma. A Ikaria et à Naxos, la croissance préférentielle du zircon entre 40 et 60 Ma localisée dans des roches provenant de zones riches en schistes indique que la pression et les circulations de fluides sont les paramètres qui ont favorisé la formation des zircons pendant le métamorphismeThe knowledge of pressure - temperature - time paths in metamorphic rocks is necessary to the understanding of orogenic belts evolution. U-Pb method is commonly used for dating metamorphic events, but the link between metamorphic conditions and ages obtained on zircon is not straightforward. Oxygen isotopes are proposed in this study for likening zircon to garnet growth in metamorphic rocks of the Aegean domain. The study of four samples from Naxos island showed that this correlation is possible if (i) isotopic equilibrium of oxygen is reached between garnet and zircon during their formation and (ii) garnet and zircon remained in closed system for oxygen and lead after their formation. This method permitted to date the beginning of the exhumation of metamorphic rocks from Naxos between 40 and 60 Ma, and the beginning of the retrograde path between 13 and 19 Ma. The preferential formation of zircon between 40 and 60 Ma in rocks localised in schist rich zones indicate that pressure and fluid circulation are the parameters that triggered zircon formation during the metamorphism
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Voice, Peter James. « The Global Detrital Zircon Database : Quantifying the Timing and Rate of Crustal Growth ». Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/27785.
Texte intégralRésumé :
Published detrital zircon geochronological data was compiled to form the Global Detrital Zircon Database (GDZDb). This database provides a reference block for provenance analysis by future detrital zircon geochronological studies. This project entailed three subprojects: 1. crustal growth/crustal recycling patterns, 2. a provenance study of the Triassic Dry Fork Formation of the Danville-Dan River Rift basin of Virginia and North Carolina, and 3. sample size issues in detrital zircon studies.
The global detrital zircon age frequency distribution exhibits six prominent, statistically significant peaks: 3.2-3.0, 2.7-2.5, 2.0-1.7, 1.2-1.0, 0.7-0.5, and 0.3-0.1 Ga. These peaks are also observed when the data is sorted for continent of origin, the tectonic setting of the host sediment and for modern river sediments. Hf isotope model ages were also incorporated into the database where grains were dated with both U-Pb and Hf isotopes. The Hf isotope model ages suggest that the majority of detrital zircons U-Pb ages reflect crustal recycling events that generated granitic magmatism, as most grains exhibited Hf isotope ages that are much older than the corresponding U-Pb age.
The Triassic Dry Fork Formation was sampled from a site in southern Virginia in the Danville-Dan River Basin. The detrital zircon age frequency distribution for this formation was strongly unimodal with a peak at 400-450 Ma and a paucity of Grenville-age zircons. Comparison of the Dry Fork sample to published east coast data and to the North American record (from the GDZDb) illustrate the unusual nature of the Dry Fork Formation sample. It is probable that older Grenville zircons were blocked from the rift valley by the rift shoulder.
Using the GDZDb a study of sample size was conducted in order to estimate the best sample size to use when trying to constrain the maximum age of sedimentation of the host sediment. Rift basins and active margins exhibited smaller offsets from the youngest zircon grain age to host sediment maximum age than observed in samples from passive margins. This study recommends that at least 50 grains need to be age dated on average in order to best constrain the age of the host sediment.Ph. D.
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Quinn, Ryan Joel. « THE EVOLUTION OF GRENVILLE BASEMENT IN THE EASTERN GREAT SMOKY MOUNTAINS ; CONSTRAINTS FROM U-PB ZIRCON GEOCHRONOLOGY, WHOLE ROCK SM-ND, AND FELDSPAR PB GEOCHEMISTRY ». UKnowledge, 2012. http://uknowledge.uky.edu/ees_etds/7.
Texte intégralRésumé :
Identifying the crustal affinity of Grenville basement rocks in the Dellwood quadrangle, western NC, provides insight into the tectonic evolution of eastern Laurentia during Grenville orogenesis. U-Pb zircon geochronology of orthogneiss, augen gneiss, and mafic xenoliths in orthogneiss reveal magmatic pulses at 1130, 1180, and 1330 Ma and metamorphic episodes at 450 and 1040 Ma. Xenoliths in 1330 Ma orthogneiss are as old as 1382 Ma and represent the oldest component of Blue Ridge basement identified to-date. Feldspar Pb isotope values span a range between juvenile-Laurentian and southern-central Appalachian basement/Amazonia. Most Pb isotope data define an array consistent with crustal mixing between Laurentia and Amazonia, however, one xenolith has a unique Pb isotopic composition interpreted as Laurentian crust. Sm-Nd isotope data yield depleted mantle model ages ranging from 1.52 to 1.79 Ga (200 to 650 Ma older than their crystallization ages) indicating a broadly non-juvenile heritage for Dellwood basement. Three biotite gneiss samples contain detrital zircon grains derived from 1060, 1160, 1330, and 1750 Ma sources. Multiple magmatic zircon age populations, variable depleted mantle modelages, and regionally unique isotopic Pb signatures are evidence of protracted Grenville magmatism in the southern Appalachians involving both Laurentian and Amazonian crustal components.
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Orme, Devon A., William R. Guenthner, Andrew K. Laskowski et Peter W. Reiners. « Long-term tectonothermal history of Laramide basement from zircon–He age-eU correlations ». ELSEVIER SCIENCE BV, 2016. http://hdl.handle.net/10150/621920.
Texte intégralRésumé :
The long-term (>1 Ga) thermal histories of cratons are enigmatic, with geologic data providing only limited snapshots of their evolution. We use zircon (U-Th)/He (zircon He) thermochronology and age composition correlations to understand the Proterozoic-Phanerozoic thermal history of Archean Wyoming province rocks exposed in the northern Laramide ranges of western North America. Zircon He ages from the Wind River Range (54 dates) and Bighorn Mountains (32 dates) show negative correlations with effective uranium (eU), a proxy for radiation damage. Zircon dates from the Bighorns are between 960 Ma (low-eU) and 20 Ma (high-eU) whereas samples from the Wind Rivers are between 582 Ma (low-eU) and 33 Ma (high-eU). We applied forward modeling using the zircon radiation damage and annealing model ZrDAAM to understand this highly variable dataset. A long-term t-T path that is consistent with the available geologic constraints successfully reproduced age-eU correlations. The best fit to the Wind Rivers data involves two phases of rapid cooling at 1800-1600 Ma and 900-700 Ma followed by slower cooling until 525 Ma. During the Phanerozoic, these samples were heated to maximum temperatures between 160 and 125 degrees C prior to Laramide cooling to 50 degrees C between 60 and 40 Ma. Data from the Bighorn Mountains were successfully reproduced with a similar thermal history involving cooler Phanerozoic temperatures of similar to 115 degrees C and earlier Laramide cooling between 85 and 60 Ma. Our results indicate that age-eU correlations in zircon He datasets can be applied to extract long-term thermal histories that extend beyond the most recent cooling event. In addition, our results constrain the timing, magnitude and rates of cooling experienced by Archean Wyoming Province rocks between recognized deformation events, including the >1 Ga period represented by the regionally-extensive Great Unconformity.
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Marsden, Ruby Connemara. « Further Development and Testing of the Combined U-Thdisequilibrium/ U-Pb and (U-Th)/He Zircon Dating Method and its Application to Quaternary Volcanic Rocks ». Thesis, Curtin University, 2021. http://hdl.handle.net/20.500.11937/88743.
Texte intégralRésumé :
Volcanic eruptions that are <1 Ma are significant for geological and archaeological investigations, however these eruptions can be challenging to date. Zircon double-dating (ZDD) is one of the few techniques that can be used to date young volcanic rocks, and combines the (U-Th)/He method with individual zircon crystallisation ages to yield eruption ages. This thesis presents several methodological improvements to the ZDD methodology and applies it to two case studies.
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Guenthner, William R., Peter W. Reiners, Henrik Drake et Mikael Tillberg. « Zircon, titanite, and apatite (U-Th)/He ages and age-eU correlations from the Fennoscandian Shield, southern Sweden ». AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/625521.
Texte intégralRésumé :
Craton cores far from plate boundaries have traditionally been viewed as stable features that experience minimal vertical motion over 100-1000Ma time scales. Here we show that the Fennoscandian Shield in southeastern Sweden experienced several episodes of burial and exhumation from similar to 1800Ma to the present. Apatite, titanite, and zircon (U-Th)/He ages from surface samples and drill cores constrain the long-term, low-temperature history of the Laxemar region. Single grain titanite and zircon (U-Th)/He ages are negatively correlated (104-838Ma for zircon and 160-945Ma for titanite) with effective uranium (eU=U+0.235xTh), a measurement proportional to radiation damage. Apatite ages are 102-258Ma and are positively correlated with eU. These correlations are interpreted with damage-diffusivity models, and the modeled zircon He age-eU correlations constrain multiple episodes of heating and cooling from 1800Ma to the present, which we interpret in the context of foreland basin systems related to the Neoproterozoic Sveconorwegian and Paleozoic Caledonian orogens. Inverse time-temperature models constrain an average burial temperature of similar to 217 degrees C during the Sveconorwegian, achieved between 944Ma and 851Ma, and similar to 154 degrees C during the Caledonian, achieved between 366Ma and 224Ma. Subsequent cooling to near-surface temperatures in both cases could be related to long-term exhumation caused by either postorogenic collapse or mantle dynamics related to the final assembly of Rodinia and Pangaea. Our titanite He age-eU correlations cannot currently be interpreted in the same fashion; however, this study represents one of the first examples of a damage-diffusivity relationship in this system, which deserves further research attention.
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Painter, Clayton S. « Sequence Stratigraphy, Geodynamics, and Detrital Geo-Thermochronology of Cretaceous Foreland Basin Deposits, Western Interior U.S.A ». Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/307071.
Texte intégralRésumé :
Three studies on Cordilleran foreland basin deposits in the western U.S.A. constitute this dissertation. These studies differ in scale, time and discipline. The first two studies include basin analysis, flexural modeling and detailed stratigraphic analysis of Upper Cretaceous depocenters and strata in the western U.S.A. The third study consists of detrital zircon U-Pb analysis (DZ U-Pb) and thermochronology, both zircon (U-Th)/He and apatite fission track (AFT), of Upper Jurassic to Upper Cretaceous foreland-basin conglomerates and sandstones. Five electronic supplementary files are a part of this dissertation and are available online; these include 3 raw data files (Appendix_A_raw_isopach_data.txt, Appendix_C_DZ_Data.xls, Appendix_C_UPb_apatite.xls), 1 oversized stratigraphic cross section (Appendix_B_figure_5.pdf), and 1 figure containing apatite U-Pb concordia plots (Appendix_C_Concordia.pdf). Appendix A. Subsidence in the retroarc foreland of the North American Cordillera in the western U.S.A. has been the focus of a great deal of research, and its transition from a flexural foreland basin, during the Late Jurassic and Early Cretaceous, to a dynamically subsided basin during the Late Cretaceous has been well documented. However, the exact timing of the flexural to dynamic transition is not well constrained, and the mechanism has been consistently debated. In order to address the timing, I produced new isopach maps from ~130 well log data points that cover much of Utah, Colorado, Wyoming and northern New Mexico, producing in the process, the most detailed isopach maps of the area. These isopach maps span the Turonian to mid-Campanian during the Late Cretaceous (~93–76 Ma). In conjunction with the isopach maps I flexurally modeled the Cordilleran foreland basin to identify when flexure can no longer account for the basin geometry and identified the flexural to dynamic transition to have occurred at 81 Ma. In addition, the dynamic subsidence at 81 Ma is compared to the position of the hypothesized Shatsky Oceanic Plateau and other proposed drivers of dynamic subsidence. I concluded that dynamic subsidence is likely caused by convection over the plunging nose of the Shatsky Oceanic Plateau. Appendix B. The second study is a detailed stratigraphic study of the Upper Cretaceous, (Campanian, ~76 Ma) Sego Sandstone Member of the Mesaverde Group in northwestern Colorado, an area where little research has been done on this formation. Its equivalent in the Book Cliffs area in eastern Utah has been rigorously documented and its distal progradation has been contrastingly interpreted as a result of active tectonism and shortening in the Cordilleran orogenic belt ~250 km to the west and to tectonic quiescence, flexural rebound in the thrust belt and reworking of proximal coarse grained deposits. I documented ~17 km of along depositional dip outcrops of the Sego Sandstone Member north of Rangely, Colorado. This documentation includes measured sections, paleocurrent analysis, a stratigraphic cross section, block diagrams outlining the evolution of environments of deposition through time, and paleogeographic maps correlating northwest Colorado with the Book Cliffs, Utah. The sequence stratigraphy of the Sego Sandstone Member in northwest Colorado is similar to that documented in the Book Cliffs area to the south-southwest, sharing three sequence boundaries. However, flood-tidal delta assemblages between fluvio-deltaic deposits that are present north of Rangely, Colorado are absent from the Book Cliffs area. These flood-tidal-delta assemblages are likely caused by a large scale avulsion event in the Rangely area that did not occur or was not preserved in the Book Cliffs area. In regards to tectonic models that explain distal progradation of the 76 Ma Sego Sandstone Member to be caused by tectonic quiescence and flexural rebound in the thrust belt, the first study shows that at 76 Ma, flexural processes were no longer dominant in the Cordilleran foreland, so it is inappropriate to apply models driven by flexure to the Sego Sandstone Member. Dynamic processes dominated the western U.S.A. during the Campanian, and flexural processes were subordinate. Appendix C. In order to test the tectonic vs. anti-tectonic basin-filling models for distal coarse foreland deposits mentioned above, the third study involves estimating lag times of Upper Jurassic to Upper Cretaceous conglomerates and sandstones in the Cordilleran foreland basin. Measuring lag time requires a good understanding of both the stratigraphic age of a deposit and the thermal history of sedimentary basin. To further constrain depositional age, I present twenty-two new detrital zircon U-Pb (DZ U-Pb) sample analyses, spanning Upper Jurassic to Upper Cretaceous stratigraphy in Utah, Colorado, Wyoming and South Dakota. Source exhumation ages can be measured using thermochronology. To identify a thermochronometer that measures source exhumation in the North America Cordillera, both zircon (U-Th)/He, on eleven samples, and apatite fission track (AFT) thermochronology, on eleven samples was performed. Typically, the youngest cooling age population in detrital thermochronologic analyses is considered to be a source exhumation signal; however, whether or not these apatites are exhumed apatites or derived from young magmatic and volcanic sources has been debated. To test this, I double dated the detrital AFT samples, targeting apatites with a young cooling age, using U-Pb thermochronology. Key findings are that the maximum depositional ages using DZ U-Pb match existing biostratigraphic and geochronologic age controls on basin stratigraphy. AFT is an effective thermochronometer for Lower to Upper Cretaceous foreland stratigraphy and indicates that source material was exhumed from >4–5 km depth in the Cordilleran orogenic belt between 118 and 66 Ma, and zircon (U-Th)/He suggests that it was exhumed from <8–9 km depth. Double dating apatites (with AFT and U-Pb) indicate that volcanic contamination is a significant issue; without having UPb dating of the same apatite grains, one cannot exclude the possibility that the youngest detrital AFT population is contaminated with significant amounts of volcanogenic apatite and does not represent source exhumation. AFT lag-times are 0 to 5 Myr with relatively steady-state to slightly increasing exhumation rates. We compare our data to orogenic wedge dynamics and subsidence histories; all data shows active shortening and rapid exhumation throughout the Cretaceous. Our lag-time measurements indicate exhumation rates of ~.9–>>1 km/Myr.
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Laurent, Antonin. « Etude pétrologique et chronométrique (U-Th-Pb) de la monazite et du zircon dans les granulites de ultra-haute température du Rogaland, Norvège ». Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30290/document.
Texte intégralRésumé :
La compréhension des processus orogéniques nécessite un couplage toujours plus étroit entre données pétrologiques visant à contraindre le trajet pression-température des roches et les données géochronologiques donnant accès aux âges et durées absolues. Cette thèse vise en premier lieu à étudier le comportement des monazites et des zircons, utilisés en géochronométrie U-Th-Pb dans les granulites de ultra-haute température (UHT) du Rogaland (sud de la Norvège). Nous montrons que la datation ponctuelle in-situ U-Th-Pb, combinée à l'analyse des éléments majeurs et traces contenus dans la monazite permet d'identifier et de quantifier deux incursions à ultra-haute température du Rogaland à 1030-1005 Ma et à 940-930 Ma. En effet, l'examen des relations de phases à l'équilibre entre monazite, xénotime et huttonite a permis de démontrer que les monazites étaient capables de cristalliser et d'enregistrer des températures supérieures à 880 °C. D'autre part, la caractérisation chimique et isotopique U-Th-Pb-O des néocristallisations et surcroissances des zircons permet de définir un intervalle de temps de 60 Ma entre les deux pics de métamorphisme, au cours duquel la croûte moyenne était partiellement fondue à des températures supérieures à 800°C et à basse pression (0.7-0.4 GPa). Ces travaux de thèse soulignent par ailleurs la variété des facteurs susceptibles de conduire à la remise à zéro, partielle ou non, des âges U-Th-Pb dans les monazites et les zircons. Nous montrons que compte tenu de l'histoire T-t du domaine étudié, le système chronométrique U-Th-Pb est largement contrôlé dans le zircon par le degré d'amorphisation de ce dernier lié à son auto-irradiation, alors que dans la monazite, ce sont les processus de dissolution-recristallisation en présence de fluides silicatés ou aqueux qui sont prépondérants. Nous montrons également qualitativement l'influence des conditions d'oxydo-réduction dans l'incorporation du S comme sulfate dans le réseau cristallin de la monazite et par conséquent le potentiel que représente la monazite pour sonder l'état d'oxydo-réduction lié aux différents évènements géologiques, dans les roches métamorphiques. Finalement, nous mettons en évidence une corrélation spatiale et temporelle entre magmatisme mantellique et métamorphisme de ultra-haute température qui ne peut être expliquée avec les modèles actuellement acceptés pour la genèse du métamorphisme de UHT. Ces observations peuvent néanmoins être expliquées en prenant en compte la différence de composition et de température du manteau Protérozoïque comparé à l'actuel, favorisant le développement d'orogènes ultra-chauds et de phénomènes gravitairesUnderstanding mountain building processes requires a better integration of petrological and peochronological data in order to link pressure-temperature paths to absolute ages. This work focuses on the behaviour of monazite and zircon, which are used as geochronometers, in ultra-high temperature granulites of Rogaland (South Norway). We show that linking in-situ U-Th-Pb dating of monazite with its major- and trace-element composition lead to the recognition of two ultra-high temperature (UHT) metamorphic events in Rogaland at c.1030-1005 Ma and c. 940-930 Ma. Indeed, the examination of monazite-xenotime-huttonite phase relationships suggests that monazite may record crystallization age at or near ultra-high temperature. Besides, the chemical and U-Th-Pb-O isotopic characterization of zircon neo-crystallization or overgrowths indicates that the Rogaland crust remains molten (> 800 °C at 0.7-0.4 GPa) at least during 60 My between the two identified UHT excursions. This manuscript also highlights the various factors responsible for U-Th-Pb (partial) resetting in the course of granulite facies metamorphism. Zircon behaviour is mostly controlled its level of amorphization, enhancing Pb loss during annealing, whereas monazite resetting is dominated by dissolution-precipitation processes in the presence of a melt or fluid phase. More specifically, we point out that monazite may be used to monitor the redox conditions of its crystallizing medium since monazite may incorporate the redox-sensitive element S in its lattice as sulphate. Finally, we demonstrate a spatial and temporal correlation between magmatism and UHT metamorphism in Rogaland. The timescale, P-T path and tectono-magmatic history however cannot be explained by currently accepted models for UHT. We suggest that physical and thermal specificities of Proterozoic mantle may explain the observed ultra-hot orogen style and the occurrence of gravity driven processes during orogeny
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Ng, Wai Pan. « Petrogenesis, U-Pb zircon geochronology and tectonic evolution of the Malaysian granite provinces in the Southeast Asian tin belt ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:0f2f3942-6d64-4a17-b194-08672107aeb2.
Texte intégralRésumé :
The Malaysian granitoids form the backbone of the Malay Peninsula and have long been recognized as composed of two distinct granitic provinces separated by the Bentong-Raub suture zone:
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Asmussen, Pascal. « Insights from the Devonian Adavale Basin on the tectonic history of the Thomson Orogen ». Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/200906/1/Pascal_Asmussen_Thesis.pdf.
Texte intégralRésumé :
This research aims to advance our understanding of the expansion of the Australian continent during the Palaeozoic. Geological remnants of specific sedimentary basins in southwest Queensland and north-western NSW were used as focus sites. A novel multi-method approach used sediment compositional information and Uranium-Lead mineral dating in combination with novel statistical methods to constrain the relative timing, sediment pathways and connectivity of these basins. The research showed that although a major period of stabilisation of the Australian continent had occurred by the beginning of the Devonian, approximately 400 million years ago, the new sedimentary basins were not yet directly connected.
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Nasdala, Lutz, Fernando Corfu, John W. Valley, Michael J. Spicuzza, Fu-Yuan Wu, Qiu-Li Li, Yue-Heng Yang et al. « Zircon M127 - A Homogeneous Reference Material for SIMS U-Pb Geochronology Combined with Hafnium, Oxygen and, Potentially, Lithium Isotope Analysis ». WILEY-BLACKWELL, 2016. http://hdl.handle.net/10150/621937.
Texte intégralRésumé :
In this article, we document a detailed analytical characterisation of zircon M127, a homogeneous 12.7 carat gemstone from Ratnapura, Sri Lanka. Zircon M127 has TIMS-determined mean U-Pb radiogenic isotopic ratios of 0.084743 +/- 0.000027 for Pb-206/U-238 and 0.67676 +/- 0.00023 for Pb-207/U-235 (weighted means, 2s uncertainties). Its Pb-206/U-238 age of 524.36 +/- 0.16 Ma (95% confidence uncertainty) is concordant within the uncertainties of decay constants. The delta O-18 value (determined by laser fluorination) is 8.26 +/- 0.06 parts per thousand VSMOW (2s), and the mean Hf-176/Hf-177 ratio (determined by solution ICP-MS) is 0.282396 +/- 0.000004 (2s). The SIMS-determined delta Li-7 value is -0.6 +/- 0.9 parts per thousand (2s), with a mean mass fraction of 1.0 +/- 0.1 mu g g(-1) Li (2s). Zircon M127 contains similar to 923 mu g g(-1) U. The moderate degree of radiation damage corresponds well with the time-integrated self-irradiation dose of 1.82 x 10(18) alpha events per gram. This observation, and the (U-Th)/He age of 426 +/- 7 Ma (2s), which is typical of unheated Sri Lankan zircon, enable us to exclude any thermal treatment. Zircon M127 is proposed as a reference material for the determination of zircon U-Pb ages by means of SIMS in combination with hafnium and stable isotope (oxygen and potentially also lithium) determination.
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Ames, Carsyn Jean. « Insights for provenance analysis of modern watersheds from detrital apatite and detrital zircon U-PB geochronology- Talkeetna Mountains, southcentral Alaska ». Thesis, University of Iowa, 2018. https://ir.uiowa.edu/etd/3244.
Texte intégralRésumé :
Detrital zircon U-Pb geochronology is a useful tool for analyzing provenance in the sedimentary record. Differentiating recycled and first cycle populations in the detrital record, however, is not a straightforward process. A second potential problem in using detrital signatures to determine provenance of sediment lies in the assumption that detrital signatures of modern rivers reflect input from each exposed unit in the catchment boundaries. To investigate each of these problems, I present U-Pb analysis of detrital zircon (DZ) from modern river sand collected from 20 watersheds, 6 detrital apatite (DA) signatures from modern river sand, and 6 DA signatures from exposed strata, all within the Talkeetna Mountains (south-central Alaska). DA rarely survives past the first cycle of erosion and deposition due to its inability to survive chemical weathering, and thus dominantly represent igneous input in detrital signatures, whereas zircon can be of igneous origin or can survive multiple cycles of erosion and deposition. By comparing the DA signatures with the DZ signatures, I present a method to better differentiate first cycle, igneous sediment contributions from recycled populations within a detrital signature. The results of these comparisons show that DA signatures provide ages of igneous input into the detrital record; these ages are also reflected in the DZ signature, thus signaling these DZ populations as igneous in origin. This study also investigates the potential for DA recycling and DA input from recycled strata. To address the second problem, I present a method using GIS software and the most recent map of Alaska to create simulated signatures that records input on a scale proportionate to the exposed surface area of each bedrock unit. In ~35% of the watersheds tested, the simulated signatures predict trends similar to the DZ signatures from the modern river sands, in 55% of the watersheds tested the simulated signatures missed one or more populations present in the DZ signature, and in 10% of watersheds tested, the simulated signature predicted trends very different from the DZ signatures. In cases where the DZ and simulated signatures do not match, I believe this represents influences of climate and relief and zircon fertility.
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Silveira, Carlos José Sobrinho da. « Geocronologia U-Pb em zircão de rochas intrusivas e de embasamento na região do Vale do Jacurici, Cráton São Francisco, Bahia ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/132001.
Texte intégralRésumé :
O Complexo Jacurici, localizado no NE do Craton São Francisco, hospeda o maior depósito de cromita do Brasil. O Complexo é constituído de várias corpos N-S, possivelmente fragmentos de um único grande sill rompido durante deformação. A idade das rochas hospedeiras é assunto de debate. Alguns trabalhos sugerem que está intruso no Bloco Arqueano Serrinha enquanto outros acreditam que é parte do Cinturão Salvador-Curaçá. Mapeamento está em desenvolvimento pela CPRM e FERBASA. Entretanto, poucos dados geocronológicos estão disponíveis para a área específica onde as rochas máfica-ultramáficas afloram. O terreno é dividido em dois segmentos chamados informalmente de paragnaisses e ortognaisses, o último supostamente mais jovem considerando estar menos deformado. Os ortognaisses ocorrem na parte norte do cinturão. Petrografia revelou que alguns dos paragnaisses são álcali-feldspato granitos fortemente milonitizados. Estes afloram relacionadas às bordas da intrusão máfica-ultramáfica na área de Ipueira. Ainda, os ortognaisses consistem, ao menos em parte, de monzogranitos com deformação de baixa temperatura. Datações de zircão por LAM-MC-ICP-MS foram realizadas para cinco amostras consideradas representativas. Apenas três resultaram em boas idades Concordia: uma rocha máfica, um monzogranito e um álcali-feldspato granito. Uma rocha máfica supostamente do embasamento produziu uma idade de 2102±5Ma e é petrograficamente similar aos metanorites descritos no Complexo Jacurici. A rocha é interpretada como registro dos primeiros pulsos do magmatismo máfico. O monzogranito gerou uma idade de 2995±15Ma, sendo mais antigo do que o esperado, relacionado ao Bloco Serrinha. O álcali-feldspato granito produziu uma idade de 2081±3Ma. O Sienito Itiúba e os pegmatitos que cortam o Complexo Jacurici tem idades semelhantes. Isto mostra uma relação muito estreita entre todas estas rochas. Considerando a falta de informações sobre a seqüência supracrustal que hospeda as rochas alcalinas e máfica-ultramáficas intrusivas nas áreas de Ipueira e Medrado, é possível que parte do terreno pertença ao Cinturão Salvador-Curaçá. Sugerimos que o Complexo Jacurici possa ter sido intrudido após a colagem tectônica entre o Bloco Serrinha e a parte mais antiga do Cinturão Salvador-Curaçá e, portanto, poderia ser hospedado por ambos.The Jacurici Complex, located in the NE of the São Francisco Craton, hosts the largest chromite deposit of Brazil. The Complex is constituted by several N-S bodies, possible fragments of a single larger sill disrupted during deformation. The age of the host rocks is still debatable. Some works suggest it is intruded on the Serrinha Archean Block while others believe it is part of the Salvador-Curaçá Belt. Mapping is under development by CPRM and FERBASA. Nevertheless, few geochronological data is available for the specific area where the mafic-ultramafic rocks outcrop. The terrain is broadly divided in two segments called informally as paragneisses and orthogneisses, the last is supposed to be younger considering it is less deformed. The othogneisses occur at the northern part of the belt. Petrography revealed that some of the believed paragneisses are actually an alkali feldspar granite strongly milonitized. It outcrops closely related to the borders of the mafic-ultramafic intrusion in the Ipueira area. Also, the orthogneisses consist, at least in part, of monzogranites with low temperature deformation. Zircon LAM-MC-ICP-MS dating were performed for five samples considered representative. Just three provided good Concordia ages: one mafic rock, one monzogranite and one alkali feldspar granite. A supposed basement mafic rock produced a 2102±5Ma age and is petrographyly similar to the metanorites described in the Jacurici Complex. The rock is interpreted as the record of the first pulses of mafic magmatism. A monzogranite yields a 2995±15Ma age, older than expected, related to the Serrinha Block. The alkali feldspar granite yields a 2081±3Ma age. The Itiúba Syenite, the Jacurici Complex and pegmatites that crosscut the Complex have similar ages. It shows a very close relationship between all these rocks. Considering the lack of information about the supracrustal sequence that hosts the intrusive alkaline and mafic-ultramafic rocks at the Ipueira and the Medrado areas, it is possible that part of the terrain belongs to the Salvador-Curaçá Belt. We suggest that the Jacurici Complex can be intruded after the tectonic amalgamation of the Serrinha Block and the older part of the Salvador-Curaçá Belt and, therefore, could be hosted by both terrains.
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Loughry, Donald Franklin Jr. « ORIGIN OF BLUE RIDGE BASEMENT ROCKS, DELLWOOD QUAD, WESTERN NC : NEW EVIDENCE FROM U-PB ZIRCON GEOCHRONOLOGY AND WHOLE ROCK GEOCHEMISTRY ». UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_theses/11.
Texte intégralRésumé :
Terrane discrimination in polycyclic continental basement rocks is challenging due to high-grade metamorphism and intense deformation. Based on early USGS mapping the Blue Ridge basement in the Dellwood quadrangle of the eastern Great Smoky Mountains was proposed to consist of augen orthogneisses of Laurentian (Grenvillian) affinity interfolded with migmatitic hornblende and biotite paragneisses (“Carolina Gneiss”) and amphibolites of uncertain affinity. However, detailed study reveals that the hornblende gneiss of Hadley and Goldsmith (1963) is a heterogeneous map unit consisting of (1)metaplutonic rocks; (2) variably foliated and folded felsic orthogneisses; (3) strongly migmatitic, folded Hbl+Bt-bearing gneisses; (4) foliated and lineated garnet amphibolites Field relations, petrology, and geochemistry demonstrate that felsic orthogneisses are related to metaplutonic rocks via (post-Taconian) progressive deformation and reconstitution. Whole rock XRF geochemistry reveals likely protoliths of Hbl gneiss and Bt gneiss are geochemically similar and have common sources. U-Pb zircon geochronology and field relationships suggest felsic orthogneisses (1050 Ma,1150-1190 Ma, 1250-1300 Ma) are components of the Mesoproterozoic Grenville basement, and not part of a metamorphosed Neoproterozoic syn-rift Laurentian margin cover sequence. A previously unknown age mode for Mesoproterozoic plutonism in the southern Appalachians was discovered (~1250-1300 Ma) suggesting the presence of a component exotic to pre-Grenvillian Laurentia (Amazonia?).
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Dilles, Zoe Y. G. « Geochronologic and Petrologic Context for Deep Crustal Metamorphic Core Complex Development, East Humboldt Range, Nevada ». Scholarship @ Claremont, 2016. http://scholarship.claremont.edu/scripps_theses/811.
Texte intégralRésumé :
The Ruby-Humboldt Range in Northeastern Nevada exposes the deepest crust in the western portion of the Sevier Hinterland. The product of unique brittle and ductile accommodations, this block of lower crustal rock is a window into the processes of continental thickening and extension. The structure of the northern tip of the Ruby-Humboldt Range core complex is dominated by a large recumbent fold nappe with a southward closeure cored by Paleoproterozoic-Archean gneissic complexes with complex interdigitated field relationships that record polyphase continental metamorphism. Amphibolite-grade metapelitic rocks within the core and Winchell Lake nappe record a wide range of zircon age dates of metamorphic events the oldest of which at ~2.5 Ga is recorded in adjacent orthogneiss as a crystallization age. At least two younger metamorphic events are recorded within this orthogneiss, most significantly at 1.7-1.8 Ga, an event previously unpublished for this region that links it to Wyoming province activity in addition to inherited component of detrital cores up to 3.7 Ga in age that is among the oldest ages reported in Nevada. The youngest overprint of cretaceous metamorphic overgrowth ranges fro 60-90 Ma in age based on zircon rims in the aforementioned units as well as three garnet amphibolites that intrude the core of the nappe and are interpreted to be metabasic bodies.
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Couzinié, Simon. « Evolution of the continental crust and significance of the zircon record, a case study from the French Massif Central ». Thesis, Lyon, 2017. http://www.theses.fr/2017LYSES035.
Texte intégralRésumé :
La formation de la croute continentale est une des conséquences majeures de la différenciation de la Terre. Les avancées récentes dans la compréhension de ce phénomène résultent de l’amélioration des techniques analytiques permettant la mesure in situ des compositions isotopiques en U-Pb-Hf-O de grains de zircon, minéral abondant dans les roches crustales. Cette étude reconstitue l’histoire du segment de croute affleurant dans l’est du Massif Central français (MCF), portion de la chaine Varisque d’Europe de l’Ouest, dans le but d’évaluer les limites d’utilisation des zircons pour retracer l’évolution crustale. L’origine et la signification géodynamique des principales unités lithologiques du MCF ont été étudiées en combinant les approches classiques de la pétrologie avec des données isotopiques U-Pb-Hf-O acquises sur zircon. Deux incohérences majeures existent entre nos résultats et les conclusions tirées de l’étude des zircons considérés hors de leur contexte pétrologique, approche généralement suivie pour analyser l’évolution crustale. Les âges modèles calculés à partir des données Hf suggèrent une importante croissance crustale au Mésoproterozoique dans le MCF, en contradiction avec le fait que 60% de la croute locale soit d’âge Néoproterozoïque. De plus, 5 à 10% de la croute du MCF a été formée durant l’orogènese Varisque sans que cela ne soit enregistré par le zircon. Dans les deux cas, ces incohérences résultent du caractère hybride des signatures isotopiques portées par les zircons. Celles-ci ne peuvent être correctement détectées et interprétées qu’en disposant de données pétrologiques complémentaires sur les roches contenant les grains analysésThe formation of the continental crust is a major consequence of Earth differentiation. Understanding how the crust formed and evolved through time is paramount to locate the vast mineral deposits hosted therein and address its influence on the global climate, ultimately affecting the development of terrestrial life. Recent advances on the topic of continental crust evolution benefited from improvements of analytical techniques enabling in situ measurements of U-Pb- Hf-O isotope compositions in zircon, a widespread accessory mineral of continental igneous rocks. The time constrains derived from the U-Pb chronometer coupled with the petrogenetic information retrieved from Hf-O isotope signatures are currently used to unravel the diversity and succession of magmatic events affecting the continental crust at the regional and global scales. This study reconstructs the evolutionary path followed by the crust segment today exposed in the eastern part of the French Massif Central (FMC), a portion of the Variscan belt of Western Europe, with the aim to investigate the potential flaws of the zircon record of crust evolution. In this scope, the origin and geodynamic significance of the constituent FMC lithological units are tackled by combining conventional petrological observations with zircon U-Pb-Hf-O isotope data. The results obtained following this integrated approach are then confronted to the conclusions that would have been drawn solely from zircon isotopic signatures, taken out of their petrological context, as is commonly performed in studies investigating crust evolution. The oldest rocks of the FMC correspond to Ediacaran (590_550 Ma) meta-sediments deposited in back-arc basins along the northern Gondwana margin. Such basins were fed by a mixed detritus originating from the adjacent Cadomian magmatic arc and a distal Gondwana source, presumably the Sahara Metacraton. Partial melting of these meta-sediments at the Ediacaran/Cambrian boundary led to voluminous S-type granitic magmatism, pinpointing a first major crust reworking event in the FMC. The origin of anatexis likely stems from the transient thickening of the hot, back-arc crust caused by the flattening of the Cadomian subduction. Subordinate melting of the depleted backarc mantle at that time is also documented. During the Lower Paleozoic, rifting of the northern Gondwana provoked coeval crust and (limited) mantle melting. Mantle-derived igneous rocks show markedly diverse trace element and isotopic signatures, consistent with a very heterogeneous mantle source pervasively modi_ed by the Cadomian subduction. Finally, the Variscan collision resulted in crustal melting as evidenced by the emplacement of S-type granites and the formation of migmatite domes, the spatial distribution of which being partly controlled by the crustal architecture inherited from pre-orogenic events. Synchronous intrusion of mafic mantle-derived magmas and their differentiates testify for Variscan post-collisional new continental crust production in the FMC. Two major inconsistencies exist between these results and the zircon record. First, zircon Hf model ages would point to substantial Mesoproterozoic crust formation in the FMC whereas more than 60% of the crust is actually Neoproterozoic in age. Second, new additions to the continental crust volume during the Variscan orogeny are not recorded even though 5 to 10% of the exposed crust formed at that time. The origin of both discrepancies inherently lies in the mixed isotopic signature carried by many zircon grains. Such equivocal information can only be detected when additional petrological constrains on the zircon host rocks are available and provide guidance in interpreting the zircon record of crust evolution
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Canile, Fernanda Maciel. « Geologia isotópica em zircões detríticos (U-Pb, Hf e O) e em rocha total (Sm-Nd e Pb-Pb) das rochas da Bacia do Paraná em Santa Catarina ». Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/44/44141/tde-24022016-140417/.
Texte intégralRésumé :
Dados isotópicos U-Pb, Hf e de O foram obtidos em zircões detríticos das unidades do final do Paleozoico e início do Mesozoico da Bacia do Paraná, sudeste do Brasil, com o objetivo de determinar a proveniência dos sedimentos, assim como contribuir para o entendimento da evolução tectônica da bacia. Assinaturas isotópicas Sm-Nd e Pb-Pb em amostras de rocha-total também foram obtidas com o intuito de auxiliar na interpretação sobre as áreas fontes. A seção estudada, Coluna White em Santa Catarina, inclui rochas de 11 unidades estratigráficas (da base para o topo): Formação Rio do Sul, Formação Rio Bonito, incluindo os membros Triunfo, Paraguaçu e Siderópolis, Formação Palermo, Formação Irati, Formação Serra Alta, Formação Teresina, Formação Rio do Rasto, subdividida nos membros Serrinha e Morro Pelado, e Formação Botucatu, Idades U-Pb foram obtidas em 1941 grãos de zircão detrítico e variam de 242 Ma a 3,4 Ga. Todas as unidades sedimentares apresentam quatro grupos principais de zircões detríticos, Neoarqueano (2,7-2.5 Ga), Paleoproterozoico Médio (2,0-1,8 Ga), Grenviliano (1,1-0,9 Ga) e Brasiliano (850-490 Ma), refletindo a importância do embasamento Pr-e-Cambriano que bordeja a parte leste da bacia como áreas fontes, tais como as Faixas Dom Feliciano, Kaoko e Namaqua-Natal, incluindo o embasamento local datado em 584 Ma. O Membro Siderópolis apresenta uma importante mudança nas fontes dos sedimentos que preencheram a Bacia do Paraná, pois é a partir dessa unidade que o pico de idade permiana (266 a 290 Ma) é observado. Esse pico persiste até o topo da seção, a Formação Botucatu. As assinaturas isotópicas de O e Hf dos zircões detríticos mostram que parte dos grãos do Paleoproterozoico Médio é provavelmente de rochas do embasamento atualmente recoberto, que estava exposto até a deposição da Formação Rio Bonito. Os isotópos de Hf e O também mostram que parte dos zircões com idade grenviliana é proveniente de rochas argentinas, o que implica em longas distâncias de transporte. As assinaturas isotópicas de parte dos grãos permianos os ligam a fontes da Argentina e Chile, sendo que parte desses grãos possui forma mais arredondada, o que sugere que eles alcançaram a bacia pelo transporte em ambientes subaquáticos e não somente pelo ar (quedas de cinzas vulcânicas) como é comumente apontado. Outros picos de idade mais jovens (Ordoviciano ao Carbonífero), observados a partir da Formação Palermo e nas unidades superiores, também são provenientes de fontes argentinas e chilenas, mostrando a importância dos detritos de fontes distantes durante o preenchimento da bacia. Os dados Sm-Nd e Pb-Pb em rocha total mostram que os sedimentos da Bacia do Paraná apresentam predominância de fontes de origem crustal. As assinaturas são semelhantes aos granitoides de Santa Catarina, rochas da Faixa Ribeira, do Escufo Brasileiro, das Faixas Namaqua-Natal e Kaoko, Terreno Arequipa-Antofalla (embasamento dos Andes) e granitoides do Norte da Patagônia. Esses dados corroboram os padrões de zircões detríticos observados, que apontam para áreas fontes tanto proximais quanto distais. Além disso, as idades modelo Sm-Nd (\'T IND. DM\') obtidas são mais antigas que 1,4 Ga e mais negativas (-10 a -15) nas unidades inferiores (Formação Rio do Sul até o Membro Paraguaçu), enquanto que as unidades superiores apresentam valores de \'\'épsilon\' IND.Nd(0) entre -6 a -12 e idades modelo \'T IND.DM\' mais jovens que 1,5 Ga, sugerindo a participação de uma fonte mais jovem a partir da deposição do Membro Siderópolis, conforme foi observado pelos dados de zircão detrítico (pico de idade permiana)U-Pb, Hf and O isotope data were obtained from detrital zircons from late Paleozoic-early Mesozoic units from Paraná Basin, southeastern Brazil, in order to constain the provenance of the sediments, as well as to contribute to the understanding of the tectonic evolution of the basin. Whole rock Sm-Nd and Pb-Pb isotopic signatures were also taken in order to help the interpretation. The studied section, White Column in Santa Catarina state, includes rocks from 11 stratigraphic units (from base to top): Rio do Sul Formation, Rio Bonito Formation (Triunfo, Paraguaçu and Siderópolis members), Palermo Formation, Irati Formation, Serra Alta Formation, Teresina Formation, and Rio do Rasto Formation (Serrinha and Morro Pelado members) and Botucatu Formation. U-Pb ages were obtained on 1941 detrital zircons and range from 242 Ma to 3400 Ma. All sedimentary units show four main detrital age groups, Neoarchean (2700-2500 Ma), mid-Paleoproterozoic (2000-1800 Ma), Grenvillian (1100-900 Ma) and Brasiliano (850-490 Ma), reflecting the importance of the Precambrian basement bordering the east side of the basin, such as Dom Feliciano, Kaoko and Namaque-Natal Belts as source areas, including the local basement that was dated at 584 Ma. The Siderópolis Member shows an important change in the source of sediments with a Permian age-peak (266 to 290 Ma). This age-peak persists towards the top of the section until the Botucatu Formation. O and Hf isotopic signatures from the detrital zircons show that a portion of the mid-Paleoproterozoic grains is probably from rocks of the presently covered basement, which was exposed until the deposition of the Rio Bonito Formation. O and Hf isotopes also show that some Grenvillian aged zircons are from Argentinian rocks, which implies a long transport distance. Isotopic signatures of part of the Permian grains also link them to sources from Argentina and Chile, and part of these grains has more rounded shapes, suggesting that they reached the basin after long distance traveling on subaquatic environment and nor only through the air (ash falls) as it is commonly accepted. Other younger age peaks (Ordovician to Carboniferous) found from Palermo Formation upsection are also linked to Argentinian and Chilean sources, showing the importance of distant sources during the filling of the basin. The Sm-Nd and Pb-Pb data on whole rocks show that the sediments from the Paraná Basin present predominance of sources with crustal origin. Osotopic signatures are similar to granitoid rocks from Santa Catarina, Ribeira Belt, Brazilian Shield, Namaqua-Natal and Kaoko Belts, as well as the Arequipa-Antofalla terranes (Andes basement) and granitoids from North Patagonia. These data corroborate the observed detrital zircon patterns thar point to both proximal and distal source areas. \'T IND.DM\' model ages older than 1.4 Ga and more negative (-10 to -15) epsilon values were observed in the lower units (Rio do Sul Formation to Paraguaçu Member), while the upper units show \'\'épsilos\' IND.Nd(0)\' values ranging from -6 to -12 and \'T IND. DM\' model ages younger than 1.5 Ga, corroborating the addition of a younger source starting from the Siderópolis Member deposition upwards, as noted by detrital zircon data (Permian age-peak).
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Reid, Mattie Morgan. « Forearc basin detrital zircon provenance of Mesozoic terrane accretion and translation, Talkeetna Mountains-Matanuska Valley, south-central Alaska ». Thesis, University of Iowa, 2017. https://ir.uiowa.edu/etd/5611.
Texte intégralRésumé :
The Wrangellia composite terrane is one of the largest fragments of juvenile crust added to the North American continent since Mesozoic time, and refining its accretionary history has important implications for understanding how continents grow. New U-Pb geochronology and Hf isotopes of detrital zircons from Late Jurassic-Late Cretaceous strata from the forearc of the Wrangellia composite terrane allows more insight on the tectonic and paleogeographic history of the terrane.
Our stratigraphically oldest samples from the Late Jurassic Naknek Formation have a detrital zircon U-Pb signature dominated by Early and Late Jurassic grains (195-190 Ma; 153-147 Ma). Hf isotopic compositions of these grains are juvenile to intermediate (εHf(t)=4.5-14.7). Disconformably above the Naknek Formation are two poorly understood units Ks and Kc. The Ks unit is dominated by Early to Late Jurassic grains (159-154 Ma) with a few Paleozoic grains (347-340 Ma). Hf isotopic compositions of Carboniferous-Jurassic grains are juvenile to intermediate (εHf(t)=6.0-18.8). The overlying Kc unit has Late to Early Jurassic zircons (198-161 Ma), and an increase in Paleozoic ages (374-323 Ma). Hf isotopic compositions of these grains are juvenile to intermediate (εHf(t)=4.5-14.7). Samples from the Matanuska Formation have major Late Cretaceous grains (90-71 Ma), and minor Early Cretaceous (137-106 Ma), Late to Early Jurassic (200-153 Ma), Paleozoic (367-277 Ma), and Precambrian grains (2597-1037 Ma). Hf compositions have a wider range from both the Late Cretaceous grains (εHf(t)=-1.5-14.9) and Paleozoic-Precambrian grains (εHf(t)=-23.7-16.3).
Our results suggest an evolving provenance from Late Jurassic to Late Cretaceous time for the Wrangellia composite terrane forearc basin. The Late Jurassic Naknek Formation samples were dominantly derived from a juvenile to intermediate Jurassic igneous sediment source. During Early Cretaceous time, there is a slight increase in the number of Paleozoic grains in the Ks and Kc unit samples. The Early Cretaceous sediments have a mostly positive Hf isotopic compositions suggesting exhumation of Jurassic and Paleozoic juvenile igneous sediment sources. By Late Cretaceous time, our data illustrates another increase in Paleozoic grain abundances, in addition to the introduction of Precambrian grains, all with widely variable Hf isotopic compositions. We interpret this to reflect a larger sediment flux from the interior of Alaska where more evolved igneous rocks of that age are found.
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Toteu, Sadrack-Félix. « Chronologie des grands ensembles structuraux de la région de Poli : Accretion crustale dans la chaîne panafricaine du Nord Cameroun ». Nancy 1, 1987. http://www.theses.fr/1987NAN10057.
Texte intégralRésumé :
Les nouvelles données structurales, géochimiques et géochronologiques indiquent un important volume de matériel d'âge protérozoïque supérieur dans le "complexe de base" et dans la "série de Poli". L'évolution tectonique et métamorphique est comparable pour les deux ensembles. Les caractéristiques géochimiques et isotopiques de l'essentiel des formations plutoniques et volcaniques de l'essentiel des formations plutoniques et volcaniques montrent qu'il s'agit de matériel juvénile nouvellement mis en place en bordure d'une croûte plus ancienne. Une chronologie des évènements panafricains est établie. Les nouveaux résultats permettent d'interprêter l'orogénèse panafricaine du Nord Cameroun en terme de tectonique des plaques
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Lobato, Marcela de Carvalho. « Proveniência sedimentar do grupo São Fidélis, terreno oriental da Faixa Ribeira com base em dados U-Pb ». Universidade do Estado do Rio de Janeiro, 2013. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=6425.
Texte intégralRésumé :
O Domínio Costeiro integra o Terreno Oriental, no segmento central da Faixa Ribeira e abriga rochas ortoderivadas com afinidade de arcos magmáticos (Complexo Rio Negro, ca. 790-605 Ma). Os ortognaisses deste complexo possuem clara assinatura para ambientes de zonas de subducção, encaixados em rochas metassedimentares de alto grau, integrantes do Grupo São Fidélis. O conjunto acima descrito é ainda intrudido por várias de rochas granitóides sin a tardi- colisionais, relacionadas às várias etapas de desenvolvimento da Orogenia Brasiliana neste setor do orógeno (ca. 605-480 Ma). Idades U-Pb (LA-ICP-MS) em zircões detríticos de rochas quartzíticas do Grupo São Fidélis indicam um amplo espectro com modas significativas no Mesoproterozóico e Paleoproterozoico, além de zircões do Neoproterozóico e do Arqueano. Sinteticamente os resultados obtidos foram: a) Idades concordantes Arqueanas com ca. 2,85, 2,84 e 2,70 Ga; b) zircões Paleoproterozóicos (ca. 2,3 a 1,7 Ga), com máxima concentração em torno de ca. 2,2 Ga, representando a segunda maior moda; c) Idades Mesoproterozóicas (ca. 1,3 -1,1 Ga) com idades de espectro dominantes, com moda em ca. 1,5 Ga; d) Zircões Neoproterozóicos com idades de ca. 0,95-90 Ga e 0,86-0,61 Ga. Em vários grãos detríticos observou-se sobrecrescimento metamórfico em ca. 602-570 Ma. Dados U-Pb (LA-ICP-MS) obtidos para zircões para Ortognaisse Rio Grande e o Biotita Ortognaisse, intrudidos na unidade basal do Grupo São Fidélis, apresentam idades em ca. 620 Ma e são equivalentes ao período pré-colisional de geração de rochas do arco magmático Rio Negro. Combinando estas idades com os núcleos de zircões detríticos mais jovens, com assinatura do Arco Rio Negro em ca. 613 Ma, pode-se definir o intervalo máximo de sedimentação da unidade superior do Grupo São Fidélis no Neoproterozóico. Cristais de monazitas selecionadas para análise U-Pb (ID-TIMS) apresentam relações com os principais episódios tectono-metamórficos da Faixa Ribeira. Dois cristais de uma amostra quartzítica e dois do ortognaisse Rio Grande alinham-se em uma discórdia que gerou idade de 603 Ma, referente ao metamorfismo progressivo descrito na literatura, durante a Orogenia Brasiliana. Enquanto a idade concordante obtida em 535 Ma, adquirida em uma amostra quartzítica, é correspontente ao último metamorfismo colisional da Faixa Ribeira.The Costeiro domain integrates the Oriental terrane of the Ribeira belt that encompasses arc related rocks of the Rio Negro complex (ca. 790-605 Ma). These orthogneisses display a well documented subduction signature and are intruded on high-grade metassedimentary rocks of the São Fidélis group. Both units are crosscut by syn to late collisional granitoids related with the development of different stages of the Brasiliano Orogeny (ca. 605-480 Ma). U-Pb (LA-ICP-MS) data of detrital zircons from quartzites of the top unit of the São Fidélis group yielded a large spectrum of ages in the Mesoproterozoic and Paleoproterozoic, with subordinated grains in the Archaean and Neoproterozoic. In a synthetic resume, the results are: a) concordant Archean ages of the ca 2,85, 2,84 e 2.70 Ga; b) Paleoproterozoic zircons with maximum in ca. 2.2 Ga (second larger peak); c) Mesoproterozoic grains with two maximums at ca. 2.3 a 1.7 Ga and ca 1.5 Ga (larger peak); d) Neoproterozoic zircons of ca. 0.95-0.90 Ga and 0.86-0.61 Ga. The youngest detrital zircon of ca 613 Ma brackets the sedimentation of the top unit. In several zircons, metamorphic overprints (tips) were identified, with ages between ca. 602-570 Ma. Data from the Rio Grande and the biotite orthogneisses, previously interpreted as belonging to the syn-collisional granites and an homogeneous layer within the basal unit of the São Fidélis Group, rendered similar ages of ca. 620 Ma and are considered as equivalents of this unit. Connecting all the obtained data a possible interpretation is that the basal unit of the São Fidélis intruded by arc related rocks were the source area for the upper unit of the group that should be interpreted as coeval with the Rio Negro Arc evolution. U-Pb (ID-TIMS) of monazite crystals yielded the two metamorphic episodes detected at central Ribeira belt. Two monazites of a quartzite together with two crystals of the Rio Grande orthogneiss are discordant, with an upper intercept of ca. 603 Ma. On the other hand one monazite of the Rio Grande orthogneiss rendered the late metamorphic episode of the belt at ca. 535 Ma.
44
Silva, Daniel Adelino da. « Geocronologia (40Ar/39Ar e U-Pb), petrografia e litogeoquímica da intrusão alcalina do Marapicu RJ ». Universidade do Estado do Rio de Janeiro, 2015. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=9115.
Texte intégralRésumé :
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorA intrusão alcalina do Marapicu é uma intrusão localizada no maciço Marapicu-Gericinó-Mendanha situado na região metropolitana do Rio de Janeiro. Este maciço é formado por dois corpos alcalinos: Marapicu e Mendanha que fazem parte do lineamento magmático Poços de Caldas-Cabo Frio. Este lineamento inclui dezenas de corpos ígneos alcalinos de idade Cretácea com uma direção preferencial WNW-ESE. Os litotipos mais abundantes do Maciço Marapicu são representados por nefelina sienitos e sienitos de caráter plutônico, além de, fonolitos caracterizados por intrusões rasas geralmente em forma de diques. Além desses litotipos foram amostradas duas rochas com características químicas de magma parental (lamprófiro e fonolito tefrítico), porém, essas duas amostras não apresentam relação genética com as demais. Também foi amostrado um nefelina sienito que possui sodalita azul como feldspatóide, sendo assim, chamado de nefelina sodalita sienito. Entre os fonolitos coletados para esse trabalho, uma amostra apresenta granada melanita em sua assembleia mineralógica, e esta foi então denominada melanita fonolito. Quimicamente as rochas do Marapicu formam uma série alcalina predominantemente insaturada em sílica, miaskítica e metaluminosa. Dentro desta série se observam duas suítes sendo uma potássica (predominante) e outra sódica. A evolução química do corpo se deu por processo de cristalização fracionada com ou sem assimilação de crosta continental provavelmente dentro de uma fonte mantélica enriquecida. Duas idades de cristalização foram obtidas para o Maciço do Marapicu sendo uma idade 40Ar/39Ar de 80,46 0,58 Ma em hornblenda, e uma idade U-Pb em zircão bastante concordante de 78,0 2,1 Ma. Os dados apresentados aqui em conjunto com dados da literatura apontam para dois modelos geodinâmicos de geração dos corpos alcalinos do sudeste brasileiro, um considera a existência de uma pluma mantélica gerada na astenosfera, o outro tem por base a hipótese de flexura crustal e considera que a carga de sedimentos depositados na plataforma continental exerceria esforços que provocariam fraturas profundas permitindo a ascenção desses magmas. O presente trabalho vem para contribuir no entendimento do alojamento dos corpos alcalinos do sudeste brasileiro através do estudo especifico do Maciço Marapicu em conjunto com dados da literatura
The Marapicu Alkaline intrusion is an intrusion into the Marapicu-Gericinó-Mendanha massif. This massif is formed by two alkaline bodies: Marapicu and Mendanha both making part of the Cretaceous Poços de Caldas-Cabo Frio magmatic lineament located in the Southeastern region of Brazil. This lineament includes tens of Cretaceous alkaline bodies and has a WNW-ESE trend. The most abundant rocks in the massif are plutonic nepheline syenites and syenites and also phonolitic rocks characterized for shallow intrusions as a dike. Besides these rocks were sampling two rocks with chemistry characteristcs of parental magma (basanite tefrite and phonolitic tefrite), nevertheless, this samples have not relationship with the others. There is also a nepheline syenite having blue sodalite as a feldspatoid called nepheline sodalite syenite. Between sampled fonolites to this work there is only sample including melanita garnet in his mineralogy assemblage and them called melanita fonolite. Chemically the Marapicu massif rocks forming an alkaline series SiO2-undersatured predominantly miaskitic and metaluminous. This series presents both potassic and sodic suites being the first one in greater content. Geochemistry data shows that evolution process involved fractional crystallization with or without continental crust assimilation and also indicates that this alkaline magma was generating into the enriched mantle source. Two crystallization age were obtained for Marapicu: 40Ar/39Ar age in hornblende of 80.46 0.58 Ma and U-Pb age in zircon of 78.0 2.1 Ma. The presented data together with literature data pointing for two geodynamic models responsible by the generation of Brazilian alkaline bodies. The first one consider there is a mantellic plume from asthenosphere, the second is based on the hypotheses of crustal flexure and consider that sedimentary charge on the continental platform would make deep fails which the magma ascending. The present work came to contribute on understanding of Brazilian alkaline bodies emplacement through the specific study of Marapicu in conjunct with literature data
45
Caquineau, Tom. « Etude géochronologique U-Pb et isotopique Lu-Hf sur zircon du groupe de Turee Creek : implications sur l’événement de grande oxygénation et les glaciations paléoprotérozoïques ». Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC236/document.
Texte intégralRésumé :
La transition Archéen – Protérozoïque (~2,45 Ga) est marquée par des bouleversements environnementaux majeurs dans l’histoire de la Terre (oxygénation de l’atmosphère et glaciations globales). Les séquences sédimentaires qui enregistrent ces événements ont été très étudiées en Amérique du Nord (séquence Huronienne) et en Afrique du Sud (Transvaal). Une séquence analogue sur le craton de Pilbara en Australie Occidentale (groupe de Turee Creek, TCG) contient 3 niveaux de diamictites glaciaires. 3 forages continentaux (Turee Creek Drilling Project, TCDP) ont été réalisés pour étudier la séquence. La géochronologie U-Pb de monazite et zircon dans des échantillons de forage et de surface a daté la première glaciation à 2,45 Ga et la seconde à ~2,34 Ga. Des analyses Re-Os de pyrites de la seconde diamictite ont donné une isochrone à 2,31 Ga. Ces résultats ont permis de proposer un scenario de corrélation des glaciations paléoprotérozoïques enregistrées sur différents continents. Une ‘Snowball Earth’ aurait eu lieu à ~2,45 Ga sur au moins 5 cratons (Pilbara, Kaapvaal, Supérieur, Wyoming, Karélia). Une seconde glaciation aurait pu avoir lieu à ~2,31 Ga sur 4 cratons. L’ensemble des zircons détritiques du TCG ont une distribution d’âge avec des pics à 2,45, 2,54, 2,68, 2,82, 2,95 et 3,2 Ga. Un cristal de zircon Hadéen a été découvert et indique la présence d’une probable croûte différenciée dans le craton de Pilbara à 4,0 Ga. 70% des zircons ont des compositions isotopiques en Hf juvéniles, suggérant que le TCG a incorporé du matériel volcanique provenant de larges provinces ignées continentales à travers l’érosion des groupes sous jacents de Hamersley et FortescueThe Archean – Proterozoic transition at 2.45 Ga is marked by major environmental changes in Earth’s history (atmosphere oxygenation and global glaciations). The origin and the relationships between these events are debated. Sedimentary sequences that record these events have been widely studied in North America (Huronian sequence) and South Africa (Transvaal). An analog sequence in the Pilbara craton in Western Australia (Turee Creek Group, TCG) contains 3 glacial horizons. 3 continental drill cores (Turee Creek Drilling Project, TCDP) were performed in order to investigate the sequence. U-Pb geochronology of monazite and zircon from drill core and surface samples allows to date the first paleoproterozoic glaciation at 2.45 Ga and a second glacial event at ~2.34 Ga. Re-Os analyses of pyrites from the second diamictite yielded an isochron at 2.31 Ga. These results enable to propose a correlation scenario of the paleoproterozoic glacial events recorded on different continents. A ‘Snowball Earth’ would have occured at 2.45 Ga at least on 5 cratons. A second glaciation could have occured at ~2.31 Ga on 4 cratons. Detrital zircons age spectrum highlights age peaks at 2.45, 2.54, 2.68, 2.82, 2.95 and 3.2 Ga. A crystal of Hadean zircon was discovered and indicate the existence of a probable differentiated crust within the Pilbara craton at 4.0 Ga. 70% of the analyzed zircons have juvenile Hf isotope composition, suggesting that the TCG incorporated volcanic material from continental large igneous provinces through the erosion of the underlying Hamersley and Fortescue groups
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Albardeiro, Luís José de Sousa. « Aplicação da geocronologia U-Pb em zircão a areias e rochas do substrato do litoral do sudoeste de Portugal : implicações para a proveniência, dinâmica sedimentar e história geológica da região ». Doctoral thesis, Universidade de Évora, 2015. http://hdl.handle.net/10174/18275.
Texte intégralRésumé :
O presente estudo de proveniência sedimentar baseia-se na geocronologia U-Pb em zircão da areia de praia (Areias Brancas, Aberta Nova e São Torpes) e, das rochas que constituem as arribas adjacentes, junto ao Cabo de Sines (grauvaques do Grupo do Flysch do Baixo Alentejo, areias da Bacia de Alvalade e sienitos do Maciço de Sines). As populações de zircão detrítico dos grauvaques carbónicos amostrados neste estudo distribuem-se principalmente pelo Neoproterozoico (ca. 844-548 Ma), derivando de fontes localizadas no bloco continental de Gondwana (Zona de Ossa-Morena). O restante flysch inclui outras fontes que podem ser atribuídas à Laurússia e a um suposto arco insular devónico; estas fontes estão relacionadas com a formação do supercontinente Pangeia (Orogenia Varisca). As idades dos zircões ígneos dos sienitos do Maciço de Sines (ca. 87-74 Ma) indicam a presença de três episódios de cristalização durante ca. 13 Ma no Cretácico Superior e as idades obtidas indicam que este Maciço é contemporâneo do magmatismo alcalino intraplaca representado pelo Maciço de Sintra. Nas areias das arribas plio-pleistocénicas da Bacia de Alvalade predominam zircões paleozoicos (ca. 541-277 Ma); são provenientes de fontes localizadas a norte (soco pré-Mesozoico da Zona Centro-Ibérica e do Eocénico-Miocénico da Bacia do Baixo Tejo), a leste (zonas de Ossa- Morena e Sul Portuguesa) e a oeste (Zona Sul Portuguesa, Triásico da Bacia do Alentejo e Maciço de Sines). Estas fontes foram expostas em resultado do rejuvenescimento do relevo por efeito da tectónica Alpina. A areia holocénica de praia, amostrada a norte do Cabo de Sines, é caracterizada pela predominância de zircões paleozoicos tal como acontece na areia plio-pleistocénica das arribas adjacentes. Na areia holocénica de praia colhida a sul do Cabo de Sines predominam os zircões cretácicos (ca. 95-73 Ma) provenientes do Maciço de Sines; esta diferenciação de fontes está relacionada com a dinâmica litoral atual;
ABSTRACT: This sedimentary provenance study is based on U-Pb geochronology of zircon extracted from beach sand (Areias Brancas, Aberta Nova and São Torpes) and sea cliffs rocks around Sines Cape (Baixo Alentejo Flysch Group greywacke, Alvalade Basin sands and Sines Massif syenites). The populations of detrital zircon from the Carboniferous greywackes (this study) are mainly distributed over the interval ca. 844-548 Ma (Neoproterozoic); they derived from sources located in Gondwana (Ossa-Morena Zone). The rest of the flysch deposits include other sources that can be attributed to Laurussia and to a supposed Devonian island arc. These sources are related to the formation of the supercontinent Pangaea (Variscan Orogeny). The ages of igneous zircons from Sines syenites (ca. 87-74 Ma) reveal three crystallization episodes during a period of ca. 13 Ma in the Upper Cretaceous; the ages obtained indicate that the Sines Massif is coeval with the Sintra Massif representing a major event of intra-plate alkaline magmatism in Iberia. Paleozoic detrital zircons (ca. 541-277 Ma) are dominant on the Plio-Pleistocene sands (Alvalade Basin) forming the sea cliffs; they derived from sources located in the north (the pre- Mesozoic basement of the Central-Iberian Zone and the Eocene-Miocene of the Lower Tagus Basin), east (areas of Ossa-Morena and South Portuguese zones) and west (South Portuguese Zone, Triassic Alentejo Basin and Sines Massif). These sources were exposed as a result of landscape rejuvenation during Alpine tectonics. The population of detrital zircons from the Holocene beach sand sampled north of the Sines Cape is dominated by Paleozoic grains as in Plio-Pleistocene sand forming the adjacent sea- cliffs. In the beach sand sampled south of the Sines Cape, Cretaceous zircons are dominant (ca. 95-73 Ma) and probably derived from the Sines Massif; this variation in sources is related to modern littoral dynamics.
47
Kobylinski, Christopher. « The Protracted Magmatism and Hydrothermal Activity Associated with the Gibraltar Porphyry Cu-Mo Deposit, South Central British Columbia, Canada ». Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39484.
Texte intégralRésumé :
The Gibraltar porphyry-Cu deposit is a large open pit porphyry Cu mine in Canada with the geological tonnage (production and reserves) of 3.2 Mt Cu. The Gibraltar deposit is hosted by the Granite Mountain Batholith (GMB), a tonalitic batholith with the surface exposure over 150 km2. All rocks within the batholith are tonalites with minor quartz diorites. The batholith intrudes into mafic volcanoclastic rocks of the Nicola group in the Quesnel terrane of the Canadian Cordillera. The Cu mineralization at Gibraltar is confined to a small 4.5 km2 area in the central part of the batholith and occurs primarily as disseminated chalcopyrite.
New U-Pb dating on zircon shows protracted late Triassic magmatism spanning ~25 m.y. for the formation of the GMB. Early magmatism is dated at 229.2±4.4 Ma in unmineralized tonalites. Later, at least three magmatism form the Cu mineralization during a period spanning from 218.9±3.1 Ma to 205.8±2.1 Ma. These fertile magmas form in a more mature arc setting, superseded early barren magmatic activity in a more juvenile arc setting for the bulk of the GMB. Epidote in the GMB shows compositional zoning with Fe-poor cores and Fe-rich rims. The zoning in the mineralized intrusions likely reflects changes in hydrothermal fluid, from S-rich to S-poor.
The data from the Gibraltar deposit shows that an economic porphyry Cu deposit may be found in igneous rocks with low Sr/Y in bulk rocks and low Eu/Eu* in zircon. In the Gibraltar deposit, Ce anomalies in zircon reflect oxidation conditions and are correlated with Cu resource associated with their respective intrusion.
48
Roberts, Richard James. « The Seiland Igneous Province, Northern Norway : age, provenance, and tectonic significance ». Thesis, 2008. http://hdl.handle.net/10539/4993.
Texte intégralRésumé :
The Seiland Igneous Province, of which 5400 km2 is exposed, is hosted within a
discrete terrane within the northernmost part of the Caledonian orogenic belt. The
Province consists of numerous mafic and ultramafic plutons emplaced into a
sedimentary succession indicative of a continental setting. Accompanying this mafic
magmatism is a significant volume of intermediate monzonitic and dioritic rock
(10% of the total exposed igneous rock), as well as numerous nepheline syenite and
carbonatitic intrusions.
This study reports ID-TIMS U-Pb analyses on magmatic zircons from a range of
intrusions, which indicate that the bulk of the Seiland magmatism took place between
560 Ma and 570 Ma, whereas previous studies had produced a range of ages between
420 Ma and 830 Ma. The data indicate that only one magmatic episode is represented
in the rocks of the Seiland Igneous Province, invalidating previous models involving
multiple rifting events over a period of 300 m.y.
Detailed geochemical investigation of several plutons from an evolved high alkali
suite of gabbroic intrusions in the Seiland Igneous Province has shown that these
plutons are generally enriched in trace elements compared to layered intrusions from
other areas across the globe, but that geochemically the gabbros are relatively
homogenous. The rocks yield εHf and εNd values for the gabbroic rocks ranging from
+8 to -6 and from +4 to -4, respectively, indicative of the contamination of mantlederived
material with crustal material. The most primitive isotopic values are similar
to those obtained from the carbonatites and nepheline syenites, indicating the same
mantle source gave rise to the magmas that were subsequently emplaced as the
Seiland Igneous Province. The homogeneous trace element content of the different
mafic rocks most likely indicates a relatively homogeneous mantle source for the
original magmas of the province, which has subsequently been affected by processes
of assimilation and crustal contamination. The monzonitic and dioritic bodies in the
Seiland Igneous Province are not derived from melted silicic crustal material and
may have been formed by the melting of pre-existing mafic material.
The new geochronology invalidates the metamorphic framework previously
proposed for the Seiland Igneous Province, which postulated several orogenic events
between the emplacement of the magmas and the Caledonian Orogeny. There is no
evidence for metamorphic activity in the period between 570 Ma and 420 Ma, and
there are monazites in gneissic rocks hosted within mafic rocks of Seiland age that
preserve an age of 640 Ma. This leads to the conclusion that only one metamorphic
event, the 420 Ma Caledonian Orogeny caused by the collision of Baltica and
Laurentia, affected the Seiland terrane after the emplacement of the Seiland magmas.
The new data obtained lead to a model for the evolution of the Seiland Province in
which a number of heavily modified and contaminated mantle-derived mafic
magmas derived from the mantle were emplaced into the continental crust of the
Seiland nappe between 560 and 570 Ma. This magmatism was accompanied by the
injection of alkaline magmas into the same area of the crust, and the melting of mafic
rock emplaced earlier. This magmatic event is considered to have occurred in an
extensional stress regime, possibly during intracontinental rifting or back-arc
spreading. This event took place well before the 420 Ma Caledonian Orogeny, and
thus the Seiland Igneous Province can be considered a remnant of an older geological
terrane that was emplaced onto the margin of Baltica during the Caledonian
Orogeny.
49
楊智宇. « Detrital Zircon U-Pb Age Study of the Guizhulin Formation in Miaoli ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/98271288484313183935.
Texte intégralRésumé :
碩士國立臺灣師範大學
地球科學系
101
The sediments of the Kueichulin Formation were deposited during Late Miocene to Early Pliocene. This formation should be able to shed some lights on the records of the transition from passive margin to foreland basin sedimentary environment in western Taiwan. This study presents U–Pb dating results of detrital zircons by single collector Laser Ablation-Inductively Coupled Plasma-Mass Spectrometer (LA-ICP-MS) to investigate the evolution of sedimentary source region during the deposition of the Kueichulin Formation near Chuhuangkeng Anticline in Miaoli. Samples were collected all the way from the Miocene Peiliao Sandstone to the Pliocene Chinshui Shale. The U-Pb dating of zircons from the Early Miocene Peiliao Sandstone to the Late Miocene Tongken Fomation display age spectra with similar major peaks at 95-165 Ma, 200-250 Ma, and 750-850 Ma. Then U-Pb dating of zircons from the terminal Miocene Shangfuchi Sandstone and Kuantaoshan Sandstone shows similar age spectra with peaks of 90-190 Ma and 200-250 Ma, which suggest that sediment supply should have changed since the terminal Miocene. According to the correlation with detrital zircon age spectra of possible sources, sediment supply of Miocene formations with abundant Proterozoic zircons should have come from the Cathaysia basement. On the contary, for that of the terminal Miocene formations, the sources would have dominantly derived from Yanshanian and granitic plutons in East Cathaysia. The results of this study suggest that the Shangfuchi Sandstone and Kuantaoshan Sandstone should have been deposited in the initial arc-continent collision between Luzon Arc and Eurasian passive continental margin. The arc-continental collision might have induced a sudden increase of the depositional slope which may have led of the noticeable change of sediment source in the terminal Miocene.
50
Zul, Zugeerbai, et 李瑞清. « Detrital Zircon U-Pb Age Study of the Paleozoic－Mesozoic Sedimentary Rocks, Southwestern Fujian ». Thesis, 2011. http://ndltd.ncl.edu.tw/handle/16271485870090207846.
Texte intégralRésumé :
碩士國立臺灣大學
地質科學研究所
99
Abstract The study is in located in the Southwest of Fujian Province, sandstone samples were collected from the Cambrian to Ordovician metamorphic rocks, and the Devonian to Jurassic sedimentary rocks. Detrital zircons of the Paleozoic-Mesozoic strata rocks were separated from10 samples by LA-ICP-MS measurements for U-Pb dating. The Southern China region undergo several plate collision, results in many phase tectonic activities, causing the variabilities of sequence stratigraphy, tectonic, and sedimentary environment. Result from the U-Pb dating, it indicates that the Jinning orogeny, Caledonian orogeny, Indosinian and Yanshanian magmatic detrital zircons re-accumulation of geological sigifcance. The comparison of these tectonic movements Caledonian, Indosinian and Yanshanian seems to slightly change of detrital zircon ages. The detrital zircon age assemblidge of Caledonian indicates that ＞2400 Ma (Wutai movement), 1700-1000 Ma, 1000-930 Ma (Sibao movement) higher proportion of about 95%. Some of igneous zircons deposite in the time without tectonic movement (1700-1000Ma). This study suggests that there remain sporadic igneous activity, such as the 750-450 Ma can be found in Fujian province during the sporadic distribution of igneous rocks. From the Caledonian movement and after, because nearly 40% from this period of igneous detrital zircons , with the result ＞750 Ma detrital zircons significantly reduced the proportion of the total, but this period is ＞2400 Ma and 850-750Ma for proportion of detrital zircon and more. The reason is Caledonian movement may cause the early Paleozoic, and Sinian strata exposed, resulting in 750-450 Ma and 850-750 Ma a higher proportion of the old in ＞2400 Ma detrital zircons more reasons, this study still can’t explain. Indosinian movement period, ＞750 Ma detrial zircon tended to decrease, probably a lot of volcanic rocks covering the surface gradually caused. But Indosinian movement 1900-1700 Ma (Luliang movement) the proportion of detrital zircons have a very high proportion of about 18%; Luliang movement is the main formation period the Catashyia, constitute the main base Catashyia, now exposed in Fujian northwest region, knows as Mayuan group. During the Indosinian movement, South China region the formation of large areas fault and folding result in a large basement area Cathaysia exposed surface, and become the main source.