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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.
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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.
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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.
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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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Liu, Chaohui, and 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.
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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
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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.
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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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Gudelius, Dominik [Verfasser], and A. [Akademischer Betreuer] Zeh. "Petrogenetic Significance of Zircon in Mafic and Felsic Rocks of the Bushveld Complex: Melt Inclusions, Physicochemical Conditions and Hf Isotopes / Dominik Gudelius ; Betreuer: A. Zeh." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1223027945/34.
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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/.
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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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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/.
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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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Guitreau, Martin. "Les isotopes de l'hafnium dans les TTG et leurs zircons : témoins de la croissance des premiers continents." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2012. http://tel.archives-ouvertes.fr/tel-00713096.
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Ce travail de thèse présente des analyses isotopiques Lu-Hf par MC-ICP-MS combinées de zircons ignés et de roches totales d'une importante collection de granitoïdes archéens appartenant à la suite des Tonalite-Trondhjémite-Granodiorite (TTG) afin d'apporter un regard nouveau sur la croissance de la croûte continentale et tout particulièrement dans le début de l'histoire de la Terre. Nos données indiquent un bon accord général entre les zircons ignés, mesurés par ablation-laser et par solution, avec leurs roche-hôtes. Nous démontrons que le rapport Lu/Hf intégré dans le temps de la source mantellique des TTG est près de la valeur chondritique et n'a pas significativement changée au cours des 4 derniers milliards d'années. Par conséquent, les continents se sont formés à partir d'un matériel primitif non fractionné extrait du manteau profond par l'intermédiaire de panaches qui après fusion partielle ont laissés un résidu appauvri dans le manteau supérieur. Les cristaux de zircon extraits des TTG ont des compositions isotopiques en Hf cohérentes au sein d'une même population alors que le système U-Pb, dans les mêmes grains, est souvent perturbé résultant ainsi en l'obtention de valeurs d'εHf initial erronées. Ce problème est endémique aux cristaux de zircon détritiques archéens et en accord avec des résultats expérimentaux sur la mobilité préférentielle de l'Hf en fonction de celle de l'U et du Pb au sein du zircon. Nous suggérons que ce problème biaise l'enregistrement détritique archéen en faveur de valeurs d'εHf initial négatives qui contrastent avec les valeurs obtenues pour les TTG mais peuvent être expliquées par l'utilisation d'âges 207Pb/206Pb non-magmatiques. Si l'on considère les cristaux de zircon de Jack Hills au vu de ces résultats, la source des continents serait restée inchangée depuis 4,3 Ga.
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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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Xia, Xiaoping. "Spot U-Pband Hf isotope analyses of detrital zircons from the khondalites in the western block of the North China craton." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B35773698.
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Xia, Xiaoping, and 夏小平. "Spot U-Pband Hf isotope analyses of detrital zircons from the khondalites in the western block of the North China craton." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B35773698.
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Luo, Yan, and 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.
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Vezinet, Adrien. "Différenciation et stabilisation de la croûte continentale archéenne, l'exemple de la marge Nord du craton du Kaapvaal en Afrique du Sud." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSES054/document.
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Le travail de thèse reporté dans ce manuscrit se focalise sur la reconnaissance ainsi que l'expression des processus de différenciation crustale à l'Archéen. Cet éon représente à lui tout seul 1/3 des temps géologiques, et se caractérise notamment par des lithologies diagnostiques, ainsi que des contextes géodynamiques complexes. La majorité des études sont portées sur l’investigation des phases alumineuses qui permettent de contraindre précisément les événements métamorphiques au-cours d’une géodynamique d’épaississement crustal. Toutefois, ces phases alumineuses représentent rarement plus de 10% des terrains archéens, alors qu’ils sont faits à plus de 75% de gneiss orthodérivés. L'étude qui suit est une caractérisation du complexe de gneiss gris composite de la marge Nord du craton archéen du Kaapvaal en Afrique du Sud. Les résultats produits durant cette investigation ont amené à plusieurs conclusions importantes au regard de la géodynamique archéenne. L'étude isotopique U-Pb/Lu-Hf sur zircon couplée à des analyses pétro-métamorphiques montre que la construction d’un complexe de gneiss gris composite correspond à une géodynamique prolongée dans le temps, accomplie au-travers de processus de différenciations crustales internes à la Zone accrétée, 1.e. le bloc crustal évolue en système thermodynamiquement fermé. Les complexes de gneiss gris ne sont que modérément étudiés toutefois, les informations contenues dans ces lithologies apparaissent complémentaires avec celles obtenues par les études métamorphiques sur les lithologies alumineuses. Il est donc nécessaire d'approfondir ce type d’investigations afin de mieux contraindre les modèles géodynamiques archéensThe PhD work presented in this manuscript focuses on the recognition and the manifestation of Archean crustal differentiation processes. The Archean eon which represents 1/3 of the geological record is featured by both lithologies unrecognized in younger eons and cryptic geodynamics. Most of investigations concentrate on the characterisation of aluminium-rich lithologies that allow an accurate determination of the pressure-temperature evolution underwent by crustal materials during crustal thickening geodynamics. However, aluminium-rich lithologies - mainly represented by metasediments - account for only 10% on average of Archean terranes whereas orthoderived gneisses - which also testify for crustal differentiation processes - form around 75% of these terranes. The following contribution depicts an Archean composite grey gneiss complex located at the northern edge of the Kaapvaal craton is South Africa. Results carried out during this PhD study have major consequences on Archean geodynamics. The zircon U-Pb/Lu-Hf isotope Investigation coupled with strong petro-metamorphic observations show that composite grey gneiss complexes may be built over a protracted time span, achieved through self-refinement of crustal materials, i.e. the crustal block evolved in a thermodynamically closed system. Grey gneiss compiexes are only moderately investigated even though information enclosed in these lithologies is complementary with those from aluminium-rich rocks. Therefore, deeper investigations of these geological objects must be a central scope in order to improve the knowledge of the Archean eon and appears necessary for the building of even more realistic geotectonic models
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Linde, G. M., J. H. Trexler, P. H. Cashman, G. Gehrels, and W. R. Dickinson. "Three-Dimensional Evolution of the Early Paleozoic Western Laurentian Margin: New Insights From Detrital Zircon U-Pb Geochronology and Hf Isotope Geochemistry of the Harmony Formation of Nevada." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/626478.
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Uranium-lead (U-Pb) geochronology and Hafnium (Hf) isotope geochemistry of detrital zircons of the Harmony Formation of north central Nevada provide new insights into the tectonic evolution of the Late Paleozoic western Laurentian margin. Using laser-ablation inductively coupled plasma mass spectrometry, 10 arenite samples were analyzed for U-Pb ages, and 8 of these samples were further analyzed for Hf isotope ratios. Three of the sampled units have similar U-Pb age peaks and Hf isotope ratios, including a 1.0-1.4Ga peak with epsilon Hf values of +12 to -3 and a 2.5-2.7Ga peak with epsilon Hf values of +7 to -5. The remaining seven samples differ significantly from these three, but are similar to one another; having age peaks of 1.7-1.9Ga with epsilon Hf of +10 to -20 and age peaks of 2.3-2.7Ga with epsilon Hf of +6 to -8. The data confirm the subdivision of the Harmony Formation into two petrofacies: quartzose (Harmony A) and feldspathic (Harmony B). The three samples with 1.0-1.4 and 2.5-2.7Ga peaks are the Harmony A, which originated in the central Laurentian craton. The other seven samples are the Harmony B, which originated in eastern Alberta-western Saskatchewan, north of the Harmony A source. We propose that all Harmony Formation strata were deposited near eastern Alberta and subsequently tectonically interleaved with Roberts Mountains allochthon strata. We interpret that the entire package was tectonically transported south along the western Laurentian margin and then emplaced eastward onto the craton during the Late Devonian-Early Mississippian Antler orogeny.
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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.
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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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Justino, Dayvisson. "Geocronologia das sub-bacias triássicas Rincón Blanco e Cerro Pontudo, Argentina: combinação de metodologia U-Pb e Lu-Hf em zircão." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/158330.
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As sub-bacias Rincón Blanco e Cerro Puntudo são depocentros pertencente à parte norte da Bacia de Cuyo, que está exposta em um terreno alóctone da Pre- Cordilheira, Andes Centrais, Argentina. Este terreno é descrito como parte do Supercontinente Laurentia, que foi adicionado ao protomargin Gondwana durante o Oroviciano. A bacia, que é um rifte Triássico, foi preenchida predominantemente de sedimentos clásticos e material vulcânico, vulcanclástico e piroclástico em ambiente continental, e é composta de vários meio-grabens assimétricos conectados por zonas de acomodação. Análises isotópicas de UPb e Lu-Hf em zircão foram realizadas nas unidades do embasamento, rochas vulcanoclásticas rochas e tufos de ambas as sub-bacias triássicas. O embasamento, representado por rochas vulcânicas andesíticas, foi datado em 269,9 ± 2,9 Ma com idades modelo de Hf de 1,34 a 1,60 bilhões de anos (Ga). As rochas vulcanoclásticas são compostas por zircões com idades de 238 a 1433 milhões de anos (Ma), com moda principal no Permiano-Triássico e Esteniano (1,0 a 1,2 Ga). Riolito e tufos triássicos formaram-se entre 246 e 230 Ma e têm idades modelo Hf variando de 1,02 a 1,50 Ga. Assim, as rochas vulcanoclásticas presentes apresentam dominantemente idades mesoproterozóicas, as quais são correlacionados ao Evento Grenviliano. Alguns grãos de zircão mostram idades modelo Hf paleoproterozóicas, que são interpretadas como sugestiva proveniência do Supercontinente Gondwana. A presença de idades mesoproterozoica dominante sugere que o magmatismo ácido associado a Bacia do Cuyo e o próprio Terreno Alóctono Cuyano tenha um embasamente Grenviliano.The sub-basins Rincón Blanco and Cerro Puntudo are depocenter belonging to the northern part of the Cuyo Basin, exposed in an allochthonous terrane of Laurentia that was added to the Gondwana protomargin and now exposed in the Precordillera Argentina. The rift basin was filled predominantly of pyroclastic and continental clastic sediments, and is composed of many asymmetric grabens half-linked by accommodation zones. U-Pb and Lu-Hf zircon isotope analyses were carried out in the basement units and volcanoclastic rocks and tuffs of both Triassic sub-basins. Basement rocks were dated at 269.9±2.9 Ma with Hf model ages 1.34 to 1.60 Ga. The volcanoclastic rocks contain zircons crystallized from 238 Ma to 1433 Ma with main peak at Permian-Triassic and Stenian (1.0 to 1.2 Ga). The Triassic rhyolite and tuffs formed between 246 and 230 Ma and have Hf model ages ranging from 1.02 to 1.50 Ga. Indeed, the volcanoclastic rocks present dominant Mesoproterozoic ages, mostly correlated to the Grenvillian. Some zircon grains show Hf Paleoproterozoic model ages which are interpreted to be part of Gondwana cratonic areas. The presence of dominant Mesoproteorzoic favored the hypotheses of a Grevillian basement for the related acid magmatism of the Cuyo Basin and allocthonous Cuyan Terrane.
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Yeshanew, Fitsum Girum. "Crustal evolution of the Arabian–Nubian Shield : Insights from zircon geochronology and Nd–Hf–O isotopes." Doctoral thesis, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-145479.
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The Arabian–Nubian Shield (ANS) represents a major site of juvenile Neoproterozoic crustal addition on Earth and documents Neoproterozoic tectonics bracketed by two supercontinent cycles, namely the fragmentation of Rodinia and the amalgamation of Gondwana. There is general consensus that the ANS formed by juvenile magmatic arc accretion and subsequent shield–wide post–tectonic magmatism. However, detailed understanding about the timing of events and the nature of magma sources in parts of the shield are lacking. To date, there are no isotopic data from the Paleozoic sedimentary sequences of the ANS, except those from the northern part. New zircon U–Pb, δ18O and whole–rock Nd isotopes are presented for plutonic rocks from the eastern Ethiopia, Yemen and southernmost Arabian Shield in Saudi Arabia. This thesis also presents the first combined in situ zircon U–Pb–O–Hf isotope data on the Cambrian–Ordovician sandstones of the Arabian Shield. The results are used to elucidate the crustal evolution of these parts of the ANS and to evaluate terrane correlations. Specifically, the nature of crustal growth, i.e., relative proportions of juvenile magmatic additions vs. crustal reworking, nature of the magma source and mechanism of crust formation (plume material vs. subduction zone enrichment) and understanding the provenance of the Cambrian–Ordovician sandstone sequences were important research questions addressed. The results from Paper I suggest that the eastern Ethiopian Precambrian basement is dominated by reworking of pre-Neoproterozoic supracrustal material unlike contemporaneous rocks in the remaining parts of Ethiopia— indicating the presence of two distinct lithospheric blocks of contrasting isotopic compositions in Ethiopia. Metamorphic age distributions suggest that the eastern Ethiopian block was amalgamated with the juvenile Western Ethiopian Shield during ca. 580–550 Ma. Importantly, the suture between them may represent the northern continuation of a major suture identified further south in Africa along which Gondwana amalgamated. Similarly, the Abas terrane in Yemen (Paper II) is dominated by reworking of pre–Neoproterozoic crust and shows age and isotopic compositions that are inconsistent with the Afif terrane of Saudi Arabia, precluding correlation between the two regions. The trace element systematics of plutonic rocks from the southernmost Arabian Shield (paper III) point to enrichment due to subduction component, bear no evidence of a plume component, and are consistent with the adakite-like chemistry of some of the subduction–related plutonic samples. This reinforces the notion that the shield grew through juvenile magmatic arc additions. The combined zircon U–Pb–O–Hf data of the Cambrian–Ordovician sandstones (Paper IV) indicate their derivation from both the adjacent juvenile ANS and the more southerly crustal blocks that are dominated by reworking of pre–Neoproterozoic crust. The remarkable similarity in age spectra and homogeneity of Cambrian sandstones deposited across the northern margin of Gondwana point to continental–scale sediment mixing and dispersal regulated by the supercontinent cycle.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.
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Jeon, Heejin. "U-Pb, Lu-Hf and O isotopes in zircon from late palaeozoic granites across orogens, Southeastern Australia." Phd thesis, 2012. http://hdl.handle.net/1885/149621.
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Southeastern Australia, part of the Phanerozoic Tasmanides, is a unique region where large amounts of granite (~30% of the surface rocks) with a very wide range of compositions (S-, I- and A-types) were intruded in the Ordovician to Triassic.
The distinctive Carboniferous granites in the Lachlan Fold Belt (LFB) are transitional in time and space between the major magmatic episodes of the LFB and New England Orogen (NEO). There was a contemporaneous continental-arc developed in the NEO, products of which became the dominant source for the NEO Early Permian S-type granites. The Carboniferous granites in the LFB have characteristic compositions (K, Sr and LILE-enrichment and Y-depletion) similar to the Late Permian I-type granites (and to the S-type granites in part) in the NEO. The in situ microanalyses of zircon (both melt-precipitated and inherited; over 1280 grains analysed from 31 samples) from those granites, using SIMS and LA-MC-ICPMS, show that the Carboniferous magmatism in the LFB was closely related to the tectonic movement of the NEO, and that the granites with similar compositions which transect the two contrasting orogens had similar source compositions.
From the isotopic compositions of zircon from the Carboniferous granites in the LFB, it is evident that the granites are distributed in zones of different ages and Hf and O isotopic compositions. The zones are approximately parallel to the NEO boundary. It is likely that tectonic activity related to the NEO triggered the production of the Carboniferous magmas and their source rocks. The new data demonstrate, however, that the Carboniferous granites were not directly related to the contemporaneous arc volcanism in the NEO. The source rocks of the Carboniferous granites in each zone consisted of different mixtures between a mantle-like underplate and relatively mature pre-existing lower crust during the Devonian.
The distinctive O isotopic compositions of inherited zircon from the NEO S-type granites demonstrate that the source rock of the granites was a Carboniferous arc-related volcanogenic sedimentary pile which included increased amounts of Devonian volcanogenic sediments with time. The age difference between the inherited and melt-precipitated zircon indicates rapid crustal recycling to produce the peraluminous magmas within 15 Ma of source rock deposition. The I-type Moonbi Supersuite granites were generated from the underplate with a minor crustal contribution. As all the studied NEO granites have remarkably similar initial Hf isotopic compositions, the components comprising most of the NEO, including sediments, are similarly radiogenic, probably due to the geologic processes operating in the young accretionary orogen.
Combining all the results of U-Pb dating and Hf and O isotopic analyses of zircon from the Carboniferous granites in the LFB and the Permian I- and S-type granites in the NEO, it is also inferred that the source rocks of the studied granites had similar isotopic compositions. This suggests a potential petrogenetic link between the granites across the two orogens. From a source composition similar to that of the most primitive LCG, three igneous components have evolved in different ways depending on the nature of the crustal materials incorporated into each component.
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Reid, B. A. "Structural, geochronological and tectonic evolution of the central Eastern Ghats Province, India: Araku-Anantagiri-Visakhapatnam." Thesis, 2010. http://hdl.handle.net/2440/102762.
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This item is only available electronically.The central Eastern Ghats Province is part of a series of terranes that collectively form the Eastern Ghats in India. The Eastern Ghats is a Mesoproterozoic to early Neoproterozoic orogen associated with the formation of the supercontinent Rodinia, c. 1.1 to 0.95 Ga. The central Eastern Ghats Province consists of metaquartzites and metapelites (khondalites) that are intruded by granitoids. The location of proto-India within Rodinia is disputed because of recently presented palaeomagnetic data. This has generated confusion about whether the protoliths to the Eastern Ghats Province metasedimentary rocks were deposited adjacent to proto-India or as an exotic terrane later accreted to India. U-Pb geochronology, in conjunction with Hf isotopes of zircons, constrain the maximum depositional age, determine provenance and identify the location of deposition. A maximum depositional age of 1.14 Ga on the protoliths to the khondalites has been determined from U-Pb zircon geochronology. The short period of time between deposition and the orogenesis related thermal event indicates that the sediments were deposited adjacent to the Bastar Craton. Provenance work identifies a number of sources within India and east Antarctica lending support to the theory that these continents were contiguous prior to the Eastern Ghats Orogeny. Structural transects and mapping reveals that shortening associated with the collision of east Antarctica and proto-India occurred along a NE-SW trending axis.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2010
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Priyatkina, Nadezhda. "The Proterozoic history of the northern and western Siberian cratonic margins based on results of U-Pb-Hf detrital zircon analysis." Thesis, 2017. http://hdl.handle.net/1959.13/1383756.
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Research Doctorate - Doctor of Philosophy (PhD)Along the western and northern margins of the Siberian Craton the Proterozoic sedimentary formations form pre-orogenic and post-orogenic sedimentary cycles, separated by a major unconformity. In various uplifts of Meso-to Neoproterozoic sedimentary rocks of Siberian cratonic margin, such as the Taimyr, the Yenisey Ridge and the Prisayan, detrital zircon signatures below the unconformity are compared with those of immature post-accretionary sedimentary rocks occurring above the unconformity. The data are further used to characterize the age of Early Precambrian basement and Neoproterozoic crust along the northern and western Siberian cratonic margins and to assist with identifying the tectonic setting of Neoproterozoic magmatic belts, their cratonic affinity and the overall geological evolution of these margins. It has been confirmed that Siberian cratonic basement is heterogenous in its age. Along the southwestern cratonic margin (Prisayan Uplift) the basins accumulated predominantly 3.4-2.7 Ga and 1.9-1.85 Ga detritus; along the western cratonic margin (Turukhansk Uplift, northern Yenisey Ridge), the basins accumulated predominantly 2.6–2.5 Ga and 1.9–1.85 Ga erosional products, while the main sources for the fill of intracratonic basin to the northeast near the Anabar Shield (East Anabar basin) were 2.9–2.7 Ga and 2.1–1.95 Ga old igneous rocks. The studied pre-orogenic rocks were mostly deposited during the Meso – to Early Neproterozoic rift-related or passive margin settings. Along with magmatic components of the Neoproterozoic crustal fringe, these rocks underwent major craton-wide recycling to produce late Ediacaran post-orogenic siliciclastic successions. Results of Hf in zircon study allow to identification of four distinct magmatic systems belt, associated with development of continental arcs at ca. 970-800 Ma and 720-600 Ma, and an oceanic arc at ca. 800-720 Ma in the Taimyr orogenic belt, and development of a long term continental arc during 950-600 Ma in the Yenisey Ridge and the north-western East Sayan. In addition to isotopic data, a geological evidence is discussed to support that Neoproterozoic crustal growth occurred near the northern and western Siberian margins and resulted in forming siginifcant portion of Arctic crust.
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Henderson, B. J. "The tectonic evolution of the Ongole Domain, India: a metamorphic and geochronological approach." Thesis, 2011. http://hdl.handle.net/2440/96173.
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This item is only available electronically.The Ongole Domain, situated in the southern Eastern Ghats Belt, exposes an assemblage of granulite facies metasedimentary and metaigneous rocks that preserve fundamental evidence for the Paleoproterozoic-Mesoproterozoic reconstruction of the supercontinent Nuna. LA-ICP-MS detrital zircon data from metasedimentary rocks constrain the timing of deposition for the sedimentary precursors, to between ca. 1850-1750 Ma. Lu-Hf isotopic data from detrital zircons provide a wide range of εHf values between -18 and +10, and TDM of ca. 3.2- 2.6 Ga. The Mesoarchean to Paleoproterozoic detrital components display geochemical similarities with the Napier Complex, the North Australian Craton and to a lesser extent, the North China Craton. U-Pb zircon and monazite geochronology have identified three episodes of metamorphism in the Ongole Domain; at ca. 1750, 1640 and 1590 Ma. Peak P-T estimates of 900 - 910°C and 9 - 9.2 kbar are calculated for metamorphism associated with collisional orogenesis, between ca. 1640-1590 Ma. Ti-in-zircon thermometry independently constrains the UHT conditions, yielding estimates of 935 ± 55°C. U-Pb geochronology and trace element analysis of zircon grains from metaigneous rocks confirm syn-tectonic magmatism occurred in the Ongole Domain between ca. 1640-1570 Ma. The results provide support for paleogeographic reconstructions that link the southern Eastern Ghats Belt and East Antarctica during the late Paleoproterozoic
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2011
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Al-Kiyumi, M. "Constraining the age and provenance of the basal quartzites of the Centralian Superbasin." Thesis, 2018. http://hdl.handle.net/2440/130321.
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This item is only available electronically.The Heavitree Formation of the Amadeus Basin, central Australia, is thought to correlate with a number of similar formations in the Officer, Ngalia, Georgina and Murraba Basins that formed the Centralian Superbasin. The Jasper Gorge Formation of the Victoria Basin and Jamison Sandstone of the Beetaloo Sub-basin are also thought to be corollaries. These formations are all constrained to being younger than ca. 1.0 Ga by U-Pb detrital zircon studies. However, in all cases, this is suspected to considerably pre-date the timing of deposition. Here, we present new U-Pb and Hf data from seven samples of the Amadeus Basin Heavitree Formation to a) better constrain the age of the Heavitree Formation, b) investigate the spatial variation in provenance of the Heavitree Formation, and, c) compare it with other ‘Supersequence 1’ quartzites from the wider Centralian Superbasin.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2018
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Robinson, Frank Alexander. "Geochronological and geochemical constraints on the lithospheric evolution of the Arabian shield, Saudi Arabia: understanding plutonic rock petrogenesis in an accretionary orogen." Thesis, 2014. http://hdl.handle.net/2440/84674.
Full textAbstract:
The Arabian-Nubian shield reflects the complex interplay between juvenile oceanic and continental arc fragments accreted during the final stages of Gondwanian super continental assembly. To date, much of the geochronological and geochemical data from the Arabian Shield, Saudi Arabia, is absent or poorly constrained and extrapolated from neighbouring Middle Eastern and African countries. Little attention has been paid to the petrogenesis and tectonic significance of the plutonic rocks pursuant to lithospheric orogenesis. A total of 137 samples from 26 geological units were collected from the Midyan, Hijaz, Asir, Tathlith, Afif, Ad Dawadimi and Ha’il terranes with particular emphasis on accretionary suture zone and within plate setting relationships. Extensive data bases are constructed using zircon U-Pb geochronology and Hf isotopes to evaluate Gondwanian significance and whole rock major and trace element geochemistry, Nd, Sm, Sr isotopes and zircon geochemistry to determine their petrogenetic properties. These parameters provide new insight into changing mantle conditions beneath collisional sutures (Yanbu, Nabitah and Halaban) and within plate asthenospheric upwelling. 19 granitic units are subdivided into metaluminous, peraluminous and peralkaline groups that possess distinguished island arc (~950-730Ma), syncollisional (~<730-636Ma), post tectonic (~<636-600Ma) and anorogenic (<600Ma) U-Pb geochronology. These magmatic phases represent accretionary cycles initiating from the dismantlement of Rodinia, closure of the Mozambique Ocean and final Gondwana amalgamation. Evidence for final assembly is recorded at ~525Ma (Najd fault reactivation) which is now the youngest dated magmatism in the Arabian-Nubian Shield and warrants repositioning of the regional unconformity at ~542Ma. Emplacement of sampled Arabian Shield classic A-type post-tectonic and anorogenic granitoids falls into three categories: 1) Intrude sutures immediately following collision which contain extensive mafic cumulate fractionation and N-MORB affiliation. 2) Plate boundary juxtaposed suites without obvious mafic cumulates, but posses contaminated N-MORB geochemistry. 3) Within plate granitoids isolated from plate boundaries and also without obvious mafic cumulates, but with a distinctive enriched (OIB) like asthenospheric mantle source. All categories produce similar felsic endmembers, but contain isotopically distinct mantle source. These are differentiated using a newly developed geochemical scheme (contaminated and enriched mantle granitoids) that is successfully applied to regional Arabian-Nubian examples. The diachronous Nabitah Orogenic Belt symbolises collision and subduction between western oceanic and eastern continental terranes that was terminated by the appearance of category 1 post-tectonic granitoids. This long lived (~50Ma) granitic magmatism contains mingling textures, discrete crystallisation ages, distinguished zircon morphologies and isotopically less juvenile mafics that geochronologically and geochemically reflect magmatic pulsing from a contaminated lower crustal MASH zone. The transition from N-MORB like mafics to isotopically enriched granitoids (isotopically similar to category 3 suites) reflects subduction magmatism followed by slab tear and asthenospheric influx. Conversely, the appearance of category 3 anorogenic plutons is characterised by widespread, tightly constrained (<10Ma) magmatism that is geochemically enriched, economic and symbolic of lithospheric delamination and asthenospheric (OIB like) upwelling. Differences between category 1, 2 and 3 zircon geochemistry constrain further contaminated and enriched mantle source behaviour that produces similar felsic products from distinguished petrogenetic processes. In summary, the work presented in this thesis establishes clear distinctions between accretionary syncollisional suites and anorogenic suites, but more significantly, post-orogenic plutons confined to suture zones from those confined to within plate settings. This allows new petrogenetic insights into changing juvenile mantle beneath the Arabian Shield.Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2014
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Hsu, Chun-Chieh, and 許鈞傑. "Detrital Zircon U-Pb and Hf Isotopic Study in Northwestern Sumatra, Indonesia." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/25561429169923275462.
Full textAbstract:
碩士國立臺灣大學
地質科學研究所
104
In NW Sumatra, Tertiary sedimentary basins that occur in forearc and backarc settings with respect to the present-day subduction system were deposited in three major terranes, namely, the Woyla Nappe, the East Sumatra block, and the West Sumatra block. NW Sumatra represents the product of complex accretion/collision/subduction histories among these three terranes, which have originated from the eastern margin of Gondwanaland. To better understand the complex histories, we present a detrital zircon study in NW Sumatra that, together with our unpublished work on major magmatic rocks in the area, allow us to reach the following conclusions: (1) Detrital zircons from 14 samples (river sand or sandstone) in the forearc basin reveal seven age peaks at ~1050 Ma (n=74), ~550 Ma (n=65), ~214 Ma (n=138), ~131 Ma (n=14), ~100 Ma (n=65), ~52 Ma (n=238) and 17-0 Ma (n=303), respectively; (2) Detrital zircons from nine samples in the backarc basin show similar age populations; (3) The Late Triassic zircons, with εHf(T) values of -18 to 0, are sourced mainly from the Indosinian granitoids that are widespread in the East Sumatra block; (4) The less abundant Early Cretaceous zircons, with εHf(T) values of -5 to 0, are most likely from the West Sumatra block; (5) The Late Cretaceous zircons, with εHf(T) values of +11 to +16, are from the Woyla Nappe due probably to the Woyla accretion; (6) The Eocene and younger zircons, with εHf(T) values of +6 to +17, are from the initial stage and modern arc magmatic rocks related to the Indian Ocean plate subduction.
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Shao, Wen-Yu, and 邵文佑. "Zircon U-Pb and Hf isotope constraints on the petrogenesis of igneous rocks in eastern Taiwan." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/54490476633081385630.
Full textAbstract:
博士國立臺灣大學
地質科學研究所
103
This thesis reports new zircon U-Pb and Lu-Hf isotopic data to better understand the petrogenesis of igneous rocks from eastern Taiwan. These include (1) volcanics from the Coastal Range, Lutao and Lanyu, (2) ophiolitic rocks from the Lichi melange, and (3) glaucophane-bearing rocks from Juisui area, the Yuli belt. Magmatic zircons yielded mean 206Pb/238U ages of 9.2 ~ 4.2 Ma for Coastal Range volcanics, ~2.6 Ma for Lanyu volcanics, ~1.3 Ma for Lutao volcanics, 17.5 ~ 14.1 Ma for east Taiwan ophiolitic rocks, and 16.0 ~ 15.4 Ma for the protolith of Juisui blueschists, respectively. We speculate that the subduction of South China Sea plate beneath the Philippine Sea plate has been initialized since ~20 Ma, and the mean inherited zircon 206Pb/238U ages of ~14.2 Ma from the Chimei igneous complex might be the earliest product of north Luzon arc magmatism. In general, magmatism in the Coastal Range had been terminated soon after the Penglai orogeny (6 ~ 5 Ma) and the final magmatism occurred at ~4.2 Ma. However, the arc magmatism of Lanyu and Lutao still spanned from Pliocene to Pliestocene. Besides, abundant inherited zircons have been obtained from the Chimei igneous complex, Yuemei volcanics, Chimei volcanics, and Lanyu volcanics, providing significant evidence for the existence of Cathaysia-affinity continental fragments rifted by the opening of the South China Sea were underneath the Luzon volcanic arc. The presence of abundant inherited zircons in volcanics suggests the magmas ascent though the old continental crust, feeding the Miocene arc, picked up the ancient zircons through assimilation or partial melting. Based on the increasing zircon uranium concentrations and the decreasing zircon εHf(T) values, we speculate that the continent-ward approach of the Manila trench allowing much more enriched continental material to involve into the mantle wedge. The magmatism of the east Taiwan ophiolite occurred during mid-Miocene, including gabbros of 17.5 ~ 17.4 Ma, diorite of 14.3 Ma and plagiogranites of 14.3 ~ 14.1 Ma. Based on the abundant inherited zircons from the ~17.5 Ma gabbro, we suggest a process of crustal contamination in ETO’s magmas during ~17.5 Ma. Moreover, the zircon Hf isotopic data indicated that the magmas were more depleted through time. In this study, we consider that the ETO originated from the highly depleted forearc magmas due to the subduction initiation of the South China Sea plate and incorporated into the Lichi melange as allochthonous blocks during the late Miocene-early Pliocene Penglai orogeny. The magmatic ages of protolith of Juisui blueschists can be well-constrained at 16.0 ~ 15.4 Ma by the zircon U-Pb ages, instead of exotic/tectonic blocks that were thought to be mid-Cretaceous or older ocean-floor fragments. Thus, we speculate that the Yuli metamorphic belt should have taken place after mid-Miocene. Based on the zircon εHf(T) variations (~32 ε-units) and whole-rock geochemistry (high MnO content), we suggest that the protolith of Juisui blueschists was product which mixed from depleted magmas (mantle-derived), enriched continental material, and Mn-rich deep-sea sediments. The protolith had undergone a high-pressure blueschist facies metamorphism and eventually rapidly exhumed and accreted to the eastern slope of the Central Range during the late Cenozoic. Briefly, the consensus of “paired metamorphic belts” of Taiwan should be thus falsified.
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Ickert, Ryan Ben. "U-Pb, Lu-Hf, and O isotope systematics of zircon from southeastern Australian Siluro-Devonian granites." Phd thesis, 2010. http://hdl.handle.net/1885/147724.
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Ishwar, Kumar C. "Mesoproterozoic Suturing Of Archean Crustal Blocks In Western Peninsular India : New Insights On India-Madagascar Correlations." Thesis, 2015. http://hdl.handle.net/2005/2651.
Full textAbstract:
The structural lineament mapping of southern India along withgeological, geochronological datasets help in redefining the Precambrian crustal blocks.The newly proposed Kumta and Mercara suture zones welding Archean crustal blocks in western peninsular India offer critical insights into the crustal evolution of Gondwana. The Kumta suturemainly consists of schistose rocks including quartz-phengite, garnet-biotite, chlorite, fuchsite and marble, whereas the Mercara suture contains mylonitic quartzo-feldspathic gneiss, garnet-kyanite-sillimanite gneiss, calc-silicate granulite and metagabbro. Metamorphic pressure-temperature estimations (Kumta suture: 11-18 kbar at 790-550oC; Mercara suture: 13 kbar at 825oC) suggest that, the sediments have undergone subduction to greater depths. The K-Ar age of biotite, phengite and U-Pb dating of zircon yields consistent metamorphic age of 1100-1400 Ma. In situ zircon 176Lu/177Hf isotope analysis shows wide range of εHf (t) values indicating the protolith sediments were derived from Paleo-Neoarchean juvenile crust that mixed with recycled older crust. The Bondla ultramafic-gabbro complex, northwest of the Kumta suture contains basalt, dolerite, gabbro, serpentinite, chromitite, peridotite and chromian spinel chemistry suggests evolution in a supra-subduction zone arc tectonic setting.The Sirsi shelf towards east of the Kumta suture, contains weakly deformed sedimentary rocks (limestone, shale, banded iron formations, greywacke, sandstone and quartzite) unconformable on relatively high-grade ca. 2571 Ma gneisses of the Dharwar craton. The Karwar block to the west is composed of weakly metamorphosedca. 3200 Ma tonalite-trondhjemite-granodiorite (TTG) with enclaves of amphibolite. In situ zircon 176Lu/177Hf isotope analysis and whole-rock 143Nd/144Nd isotopic analysis of TTGs show positive εHf and εNd values indicating ca. 3200 Ma juvenile crust. The Coorg block consists of ca. 3200 Ma charnockite, mafic granulites, hornblende-biotite gneiss, garnet-hornblende gabbro and anorthosite.In situ zircon 176Lu/177Hf isotope analysis indicates source as mixture of juvenile crust and older recycled crustal materials. Synthesis of the above results with published data suggests that Kumta and Mercara suture zones incorporate Paleoarchean to Mesoproterozoic sedimentssubjected to high-pressure metamorphism in the late Mesoproterozoic. Metamorphic P-T estimations of mafic granulite and U-Pb zircon geochronology of pelitic gneisses from Betsimisaraka suture zone, Madagascar suggests the rocks were underwent metamorphism at c. 24 kbar and c. 780°C during Mesoproterozoic suturing of Antongil-Masora blocks with the Antananarivo block.From the integration of above results with the new geophysical results and published data Mesoproterozoic Kumta-Mercara suture is interpreted as eastern extension of the Mesoproterozoic Betsimisaraka suture of Madagascar into western India.
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Howard, K. E. "Provenance of Palaeoproterozoic metasedimentary rocks in the eastern Gawler Craton, Southern Australia: Implications for reconstruction models of Proterozoic Australia." Thesis, 2006. http://hdl.handle.net/2440/123593.
Full textAbstract:
This item is only available electronically.Detrital zircon ages obtained from the Corny Point Paragneiss and the Massena Bay Gneiss in the southeastern Gawler Craton, Australia, constrain their deposition to the interval ca. <1880 Ma. The presence of 2020 Ma, 2450 Ma and 2520 Ma detrital zircons within the Corny Point Paragneiss constrains the source region for the sedimentary protoliths to three possible domains within Australia; the Gawler Craton, the Glenburgh Orogen in the Western Australian Proterozoic, and the North Australian Craton, all of which contain rock systems with similar ages. Whole rock εNd (1850Ma) values from the Corny Point Paragneiss range from -1 to -5. These values potentially preclude the Late Archaean to mid Proterozoic crust of the Gawler Craton as a sole or major source region due to its highly evolved average εNd (1850Ma) of around -10. Preclusion of the Gawler Craton as a source is apparently confirmed by Hf isotopic compositions of 2020 Ma detrital zircons from the Corny Point Paragneiss, which have εHf (2020Ma) ranging between +3 to +7. This compares with εHf (2020Ma) of -1 to -4 for zircons from the 2020 Ma Miltalie Gneiss in the Gawler Craton. Available Nd isotopic data suggests that the Glenburgh Orogen is too crustally evolved to have provided the majority of sediment into the Corny Point Paragneiss protolith. The 2020 Ma detrital Hf isotopic compositions of the Corny Point Paragneiss are similar to the 2020 Ma Wildman Siltstone (εHf (2020Ma) +2 to +7) in the Pine Creek Orogen in the North Australian Craton. Two possible scenarios can be extrapolated from the detrital zircon and Nd isotopic data; (1) the Corny Point Paragneiss sediment was derived from a source region within the North Australian Craton and could share source regions with the Wildman Siltstone, or (2) the sediments were derived from a Gawler Craton source region that included a dominant juvenile component of the 2020 Ma Miltalie Gneiss in the adjacent Gawler Craton which has since been eroded. In the first scenario, the absence of connection to the Gawler Craton allows for the Betts and Giles (2006) plate reconstruction model, which proposes that the Corny Point Paragneiss formed part of the North Australia Craton, and was sutured to the Proto Gawler Craton at 1730-1700 Ma. The second scenario highlights a significant limitation in evaluating the significance of provenance data, particularly when considering old potential source terrains that have undergone significant levels of denudation. The proximity of the Corny Point Paragneiss to the rifted southern and eastern margins of the Australian Proterozoic means a thorough evaluation of the palaeogeographic significance of the Corny Point Paragneiss detrital signature requires corresponding datasets from regions such as Antarctica which were formerly contiguous with the Gawler Craton.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2006
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Chiu, Han-Yi, and 邱瀚毅. "The Neotethyan subduction and Zagros orogeny:constraints from zircon U-Pb age and Hf isotopic study ofmagmatic rocks from Iran." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/76570780192304152961.
Full textAbstract:
博士國立臺灣大學
地質科學研究所
101
This study reports the first combined LA-ICPMS analyses of zircon U-Pb and Hf isotope compositions for magmatic rocks from several major domains of Iran, including the Urumieh-Dokhtar magmatic arc (UDMA), Sanandaj-Sirjan structural zone (SSZ), Alborz Range, Central Iran and Sistan suture zone. These results, together with the literature data and some unpublished ages of our team, better delineate the magmatic evolution related to the Neotethyan subduction and subsequent Zagros orogeny that resulted from the Arabia-Eurasia collision. Moreover, this study also identifies two major magmatic events that formed during the late Neoproterozoic to Cambrian and the Late Triassic before the occurrence of broad magmatic activities which are related to the Neotethyan subduction. The first magmatic event represents a depleted mantle-derived magmatic feature and it has associated with the magmatism that produced the peri-Gondwanan terranes and Arabian-Nubian Shield. The second magmatic event is attributed to the Paleotethys evolution and shows an obvious magmatic signature of crustal contamination. The Neotethyan subduction-related magmatism was active during the Jurassic time, as evidenced by the presence of widespread I-type granitoids from the Middle to Late Jurassic (176-144 Ma) in the SSZ. These intrusive rocks, also exposed in the central part of the UDMA and the northern Lut block, show a heterogeneous isotopic affinity with variable zircon εHf(T) values between +12 and -5. After a protracted magmatic quiescence in the Early Cretaceous, the igneous activity renewed inland in the UDMA from which the Late Cretaceous granitoids (81-72 Ma) are found in the southeastern segment of the UDMA. These rocks from the Jiroft and Bazman areas have very different zircon εHf(T) values clustering from +15 to +11 and from +5 to -9, respectively, implying that the Bazman magmas were significantly mixed with the old crustal components. Then, the UDMA volcanism was most active and widespread during the Eocene and Oligocene (55-25 Ma), much longer lasting than the previously thought as just an Eocene pulse. Such a prolonged igneous “flare-up” event in the UDMA can be correlated to Armenia where the coeval calc-alkaline rocks are common. Similar ages are also obtained from the magmatic rocks in the northwestern SSZ and west Alborz. This magmatism, with mostly positive zircon εHf(T) values between +17 and -1, can further signify the formation of extensive juvenile crust in the regions owing to the Neotethyan subduction. The magmas with a primitive signature were also exposed in the southern Sistan suture zone and the Makran region during the Oligocene to Quaternary (32-1 Ma). By contrast, the ancient continental crust material was observed from the Central Iran, in Saghand area by the Eocene granitoids that yielded less radiogenic zircon Hf isotopes of εHf(T) values ranging from +6 to -7. The UDMA magmatism ceased progressively from the northwest to the southeast, with the magmatic activities ending in the Early Miocene (ca. 22 Ma) in Meghri, in the Middle Miocene (ca. 16 Ma) in Kashan and in the Late Miocene (ca. 10-6 Ma) in Anar. The southeastward magmatic cessation is consistent with the notion of the oblique and diachronous continental collision between Arabia and Eurasia. The post-collisional volcanism started at ca. 11 Ma in Saray, east off the Urumieh Lake, which, along with the later eruptions in Sahand (6.5-4.2 Ma) and Sabalan (≤0.4 Ma) volcanoes, forms a compositionally unique component of the vast volcanic field covering much of the Lesser Caucasus, NW Iran and eastern Anatolia regions.
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Hiess, Joseph. "Early crustal petrogenesis : integrated in situ U-Pb, O, Hf and Ti isotopic systematics of zircon from Archaean rocks, West Greenland." Phd thesis, 2008. http://hdl.handle.net/1885/150388.
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Chen, Bei. "Growth of the Preserved Continental Crust: Integrated U-Pb, O, and Hf isotopic systematics of detrital zircons from Australia and Antarctica." Phd thesis, 2022. http://hdl.handle.net/1885/267270.
Full textAbstract:
When and how the continental crust was generated, and how the volume of the continental crust has changed with time, are fundamental questions in Earth Sciences. Various models for the growth of the continental crust have been proposed, but there is no consensus yet, highlighting the complexity of continental growth. In-situ analyses of U-Pb, O and Lu-Hf isotopes from detrital zircon grains from the world's major rivers can potentially capture the approximate timing of major formation of the felsic continental crust. The U-Pb age of igneous zircon records the time when the source magma crystallized. Lu-Hf isotopes in zircon can be used to calculate a model age of the source magma from which the zircon crystallized: the time when the source material was extracted from the mantle. O isotopes in magmatic rocks are highly sensitive to the incorporation of supracrustal material, which has been subjected to low-temperature processes, especially clays produced by weathering, into a magma source region. O isotopes can be used to indicate the involvement of sediments, which influences the Lu/Hf ratio of the source region, required for model age calculations. In this study, detrital zircons from Antarctica and Australia were analyzed for U-Pb, O and Lu-Hf isotopic compositions to investigate the crustal growth of the two continents and the major tectonic events that have affected these continents. And combined with other datasets from Asia, Africa and North America, using the similar method adopted in this study, the results make it possible for the global growth curve of the present continental crust to be reconstructed.
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Castillo, Gonzalez Paula Alejandra. "Evolution of the patagonian-west antarctica margin of gondwana in the palaeozoic–early mesozoic: new models constrained by zircon u-pb ages, and o and hf isotopic compositions." Phd thesis, 2016. http://hdl.handle.net/1885/130073.
Full textAbstract:
A number of conflicting tectonic models have been proposed to
explain the geological relationships between southern South
America (Patagonia) and West Antarctica within the palaeo-Pacific
margin of Gondwana. Extensive fragmentation and isolation of the
various tectonic blocks during Gondwana break-up have complicated
interpretations and palaeogeographic reconstructions. In order to
explore and test the different tectonic models, I combine zircon
U-Pb, Lu-Hf and O isotopic data for samples from key locations
throughout the north and south of Patagonia, the Antarctic
Peninsula and the Ellsworth Mountains in West Antarctica. Zircon
is a robust refractory mineral that occurs in igneous and
metamorphic rocks and survives multiple sedimentary cycles with
little change to its isotopic composition. It therefore preserves
a perfect archive for testing tectonic correlations.
Igneous rocks from the Ellsworth Mountains were dated at ca. 680
Ma, older than previously reported. These zircons indicate that
rifting, which affected Mesoproterozoic crust, likely occurred in
the Cryogenian and supports a connection between the
Ellsworth-Whitmore Mountain block and East Antarctica before the
amalgamation of Gondwana. This agrees with the break-up of
Rodinia in the context of the southwest United States and East
Antarctica configuration. U-Pb zircon dating and O-Hf isotopic
compositions of detrital zircons from the Ellsworth Mountains
also support this connection, indicating a likely East Antarctic
provenance. A Cambrian magmatic event is recorded by zircon at
ca. 520 Ma, also related to an extensional setting – but in
this case with crustal recycling. I interpret this Cambrian
magmatism as a result of a tectonic escape after a collision
between the Australo-Antarctic and West Gondwana/Indo-Antarctic
plates.
In Tierra del Fuego, samples from drill cores indicate that
Cambrian magmatism occurred between ca. 540 and 520 Ma with
strong similarities to the Pampean Orogen of Argentina.
Metamorphism occurred at ca. 265 Ma, when zircon crystallised
from high temperature hydrous fluids that previously interacted
with Grenvillian rocks. Importantly, igneous rocks from Tierra
del Fuego record the first evidence of Permian magmatism at ca.
255 Ma, arising from melting of Cambrian rocks. This suggests
prolongation of Permian magmatism from the North Patagonian
Massif in northern Patagonia and also connections to the Eastern
Domain of the Antarctic Peninsula. Granitic rocks in northern
Patagonia record mantle-like O magmatic inputs at ca. 280 Ma and
255 Ma, but with reworking of upper crustal materials between
these two events. In northwestern Patagonia, early Permian
granites indicate continuity of the Permian magmatic belt along
the western margin of South America farther north. Further,
detrital Permian zircons in late Palaeozoic–early Mesozoic
accretionary complexes suggest a continuation of a slightly older
Permian subduction-related magmatic arc, partly located in
Patagonia and extending to the Antarctic Peninsula.
All this data, together with other geological considerations, are
in line with an autochthonous or parautochthonous origin for
northern Patagonia. It also confirms connections between southern
Patagonia and the Antarctic Peninsula from late Palaeozoic to
Jurassic times. I suggest that Patagonia rifted from the South
African-Ellsworth sector of the paleao-Pacific margin of Gondwana
to then collide with the same sector during the Guadalupian.
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Klama, Kai Olaf [Verfasser]. "U-Pb-Geochronologie, Hf-Isotopie und Spurenelementgeochemie detritischer Zirkone aus rezenten Sedimenten des Orange- und Vaal-River-Flusssystems in Südafrika / von Kai Olaf Klama." 2008. http://d-nb.info/994793383/34.
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