Academic literature on the topic 'Detrital peaks'
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Journal articles on the topic "Detrital peaks"
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Vozárová, Anna, Katarína Šarinová, Dušan Laurinc, Elena Lepekhina, Jozef Vozár, Nickolay Rodionov, and Pavel Lvov. "Exhumation history of the Variscan suture: Constrains on the detrital zircon geochronology from Carboniferous–Permian sandstones (Northern Gemericum; Western Carpathians)." Geologica Carpathica 70, no. 6 (December 1, 2019): 512–30. http://dx.doi.org/10.2478/geoca-2019-0030.
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Abstract The Late Paleozoic sedimentary basins in the Northern Gemericum evolved gradually in time and space within the collisional tectonic regime of the Western Carpathian Variscan orogenic belt. The detrital zircon age spectra, obtained from the Mississippian, Pennsylvanian and Permian metasediments, have distinctive age distribution patterns that reflect the tectonic setting of the host sediments. An expressive unimodal zircon distribution, with an age peak at 352 Ma, is shown by the basal Mississippian metasediments. These represent a relic of the convergent trench-slope sedimentary basin fill. In comparison, the Pennsylvanian detrital zircon populations display distinct multimodal distributions, with the main age peaks at 351, 450, 565 Ma and smaller peaks at ~2.0 and ~2.7 Ga. This is consistent with derivation of clastic detritus from the collisional suture into the foreland basin. Similarly, the Permian sedimentary formations exhibit the multimodal distribution of zircon ages, with main peaks at 300, 355 and 475 Ma. The main difference, in comparison with the Pennsylvanian detrital zircon assemblages, is the sporadic occurrence of the Kasimovian– Asselian (306–294 Ma), as well as the Artinskian–Kungurian (280–276 Ma) igneous zircons. The youngest magmatic zircon ages nearly correspond to the syn-sedimentary volcanic activity with the depositional age of the Permian host sediments and clearly indicate the extensional, rift-related setting.
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Chang, Zhe, Zhiqian Gao, Liangliang Zhang, Tailiang Fan, Duan Wei, and Jingbin Wang. "Provenance of Ordovician Malieziken Group, Southwest Tarim and Its Implication on the Paleo-Position of Tarim Block in East Gondwana." Minerals 13, no. 1 (December 27, 2022): 42. http://dx.doi.org/10.3390/min13010042.
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Tarim is inferred to have a close connection with East Gondwana during the Ordovician, but the position in East Gondwana remains controversial. In this study, we report 316 detrital zircons U-Pb data from three samples of Ordovician Malieziken Group sedimentary rocks, collected in the Qiate Section, Southwest Tarim, provided new insight into the position of Tarim in East Gondwana. Detrital zircons data indicated the maximum depositional age for the three samples is 489.5 Ma, 478.1 Ma, and 465 Ma, respectively, indicating the Qiate and Kandilike Formation of the Malieziken Group was deposited in Early—Middle Ordovician. The detrital zircons are characterized by two main peaks at ~490 Ma and ~1100 Ma, and three subordinate peaks at ~880 Ma, ~1400 Ma, and ~1650 Ma, suggesting most of the detritus of Malieziken Group from the South Kunlun Terrane (SKT) itself. However, the source of the ~1650 Ma peak is not found in the Tarim block, and the ~1400 Ma and the ~1650 Ma peak are absent in the middle of the three samples, which implied that there is an exotic source. The Paleoproterozoic sediment strata in the Albany–Fraser belt shows dominant peaks at ~1400 Ma and ~1650 Ma may have been transported to SKT and redeposited in the Malieziken Group during the Ordovician. The Malieziken Group shows detrital zircon age patterns resembling those of East Sumatra, Lhasa, and Western Australia which, in combination with the Albany–Fraser belt provenance, enables us to propose that the Tarim block has a close linkage with Western Australia, East Sumatra, and Lhasa in East Gondwana.
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Xu, Zhongjie, Yizhi Lan, Jintao Kong, Rihui Cheng, and Liaoliang Wang. "Detrital zircon U–Pb dating of Late Triassic Wenbinshan Formation in southwestern Fujian, South China, and its geological significance." Canadian Journal of Earth Sciences 55, no. 8 (August 2018): 980–96. http://dx.doi.org/10.1139/cjes-2018-0007.
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Based on research of the petrology, geochemistry, and zircon U–Pb dating of detrital rocks in the Late Triassic Wenbinshan Formation in southwestern Fujian, and comparing the detrital zircon ages of Wenbinshan Formation with those of Late Paleozoic – Early Mesozoic main basins in South China, the sedimentary provenance of the Late Triassic in southwestern Fujian and its implications for changes in basin properties are discussed. The research results demonstrate that there is a major age peak at 222 Ma, two subordinate age peaks at 275 Ma and 1851 Ma, and two minor age peaks at 413 Ma and 2447 Ma in the detrital zircon age spectra of the upper samples (YGP–6) of the Wenbinshan Formation, whereas there are two major age peaks at 229 Ma and 1817 Ma and other minor age peaks 265 Ma 309 Ma, 415 Ma, 1968 Ma, and 2435 Ma in the detrital zircon age spectra of the lower samples (YGP–26) of the Wenbinshan Formation. The upper samples contain fewer old detrital zircons than the lower samples, but the upper and lower samples of Wenbinshan Formation are similar in major age composition, which indicates the main provenances of the upper and lower sediments are very similar. The source rocks are mainly sedimentary rocks and their provenances are derived from a source area of recycled orogenic belt and volcanic arc orogenic belt (acidic island arc). The detrital zircon composition of the Wenbinshan Formation is mainly composed of Paleoproterozoic zircon and Late Paleozoic – Early Mesozoic zircon. In the Paleoproterozoic, sedimentary provenances were mainly derived from the Wuyi Massif and partly from northwestern Fujian-southwestern Zhejiang. As for the period of Late Paleozoic – Early Mesozoic, the provenances of the Wenbinshan Formation were derived from magmatic active belts of the Early Indosinian Epoch of northern South China, eastern South China, and the Indosinian Period of northern South China and coastal areas of eastern South China. The similarities and differences between detrital zircon age peaks of the Wenbinshan Formation in southwestern Fujian and that of the main basins in South China during the period of Late Paleozoic – Early Mesozoic indicate that from eastern coastal areas of South China to the north and interior of South China, the age composition of basin sediments has changed from simple to relatively complex, and from young sediments to older sediments. There are similarities and differences in the detrital zircon compositions of the different basins, which can indicate differences in the nature of the basins.
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Thomas, William A., George E. Gehrels, Timothy F. Lawton, Joseph I. Satterfield, Mariah C. Romero, and Kurt E. Sundell. "Detrital zircons and sediment dispersal from the Coahuila terrane of northern Mexico into the Marathon foreland of the southern Midcontinent." Geosphere 15, no. 4 (June 26, 2019): 1102–27. http://dx.doi.org/10.1130/ges02033.1.
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AbstractNew analyses of U-Pb ages along with previously published analyses of detrital zircons from sandstones in the foreland of the Marathon orogen in west Texas have significant implications regarding provenance. The most prominent concentrations of U-Pb ages are at 1200–1000, 700–500, and 500–290 Ma. The accreted Coahuila terrane in the Marathon hinterland and nearby terranes with Gondwanan (Amazonia) affinity include Paleozoic volcanic and plutonic rocks, as well as Precambrian basement rocks. Late Paleozoic Las Delicias arc rocks have ages of 331–270 Ma. Detrital zircons from Upper Jurassic and Lower Cretaceous sandstones, which were deposited in local basins around the Coahuila terrane, provide a record of detritus available from proximal sources within Coahuila, including important peaks at 1040, 562, 422, 414, 373, and 282 Ma. Components of the detrital-zircon populations in the Marathon foreland have unique matches with primary and/or detrital sources in the Coahuila terrane. Although some components of the Marathon populations also have age matches in Laurentia (Appalachians), others do not; however, all components of the Marathon populations have potential sources in Coahuila. Analyses of εHft show generally more negative values in Amazonia than in Laurentia, and εHft values for Marathon sandstones have distributions similar to those in Amazonia. Therefore, the Coahuila terrane provides a provenance for all of the detrital-zircon ages in the Marathon foreland, requiring no mixing from other sources.
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Papapavlou, K., A. Moukhsil, A. Poirier, and J. H. F. L. Davies. "The Pre-Grenvillian assembly of the southeastern Laurentian margin through the U–Pb–Hf detrital zircon record of Mesoproterozoic supracrustal sequences (Central Grenville Province, Quebec, Canada)." Geological Magazine 159, no. 2 (November 15, 2021): 199–211. http://dx.doi.org/10.1017/s0016756821001023.
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AbstractThe detrital zircon perspective on the pre-collisional crustal evolution of the Grenville Province remains poorly explored. In this study, we conducted in situ laser ablation U–Pb–Hf isotopic microanalysis on detrital zircon grains from three pre-orogenic (>1 Ga) supracrustal sequences that crop out in the Central Grenville Province (Lac Saint-Jean region, QC, CA). Detrital zircon grains from vestiges of these sequences record three dominant age peaks at c. 1.46 Ga, 1.62 Ga, 1.85 Ga, and a subordinate peak at 2.7 Ga. The 1.46 Ga and 1.62 Ga age peaks are recorded in detrital zircon grains from a quartzite associated with a metavolcanic sequence (i.e. Montauban Group) with a maximum depositional age of c. 1.44 Ga. In contrast, the c.1.85 Ga age peak is observed from recycled zircon grains in metasediments with maximum depositional ages between 1.2 and 1.3 Ga. The suprachondritic Hf isotope composition in detrital zircon grains of the 1.46 Ga and 1.62 Ga age populations records juvenile crustal growth during peri-Laurentian accretionary orogenesis related to the Pinwarian (1.4–1.5 Ga) and Mazatzalian–Labradorian (1.6–1.7 Ga) events. The detrital zircon grains associated with Penokean–Makkovikian (1.8–1.9 Ga) source rocks record reworking of c. 2.7 Ga continental crust derived from a near-chondritic mantle reservoir. Overall, crust-forming and basement reworking events associated with accretionary orogenesis in southeastern Laurentia are retained in the detrital zircon load of Precambrian basins even after the terminal Grenvillian collision and assembly of Rodinia.
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Kanygina, N. A., A. A. Tretyakov, K. E. Degtyarev, K. N. Pang, K. L. Van, H. Y. Lee, and J. V. Plotkina. "First results of dating detrital zircons from the late precambrian quartzite-schist sequences of Chu block (Southern Kazakhstan)." Доклады Академии наук 489, no. 1 (November 10, 2019): 57–61. http://dx.doi.org/10.31857/s0869-5652489157-61.
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U-Pb geochronological studies of detrital zircons from quartzite-schist sequences of the Akbastau Formations of the Chu block (northwest of the Chu-Kendyktas terrane, Southern Kazakhstan) have been provided. The concordant ages of detrital zircons are predominantly within the intervals of 1672-2115 Ma with peaks at 1697, 1780, 1857 and 2066 Ma. Individual zircon grains display ages of 2291-2332 Ma with peaks at 2303 and 2322 Ma. Neoarchean ages 2608-2747 with peak at 2681 Ma characterize another significant zircon population. The lower limit of deposition for the Akbastau Formations of the Chu block, corresponding to the youngest statistically significant zircon population, is estimated at 1,7 billion years.
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Ovchinnikov, R. O., A. A. Sorokin, V. P. Kovach, and A. B. Kotov. "Geochemical features, sources and geodynamic settings of accumulation of the cambrian sedimentary rocks of the Mel’gin trough (Bureya continental massif)." Геохимия 64, no. 5 (May 23, 2019): 503–19. http://dx.doi.org/10.31857/s0016-7525645503-519.
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The first data about geochemical features of the Cambrian sedimentary rocks of the Mel’gin trough of the Bureya continental Massif, as well as ages of detrital zircons of them are obtained. It is established, that among the detrital zircons from the sandstones of the Chergilen and Allin formations of the Mel’gin trough zircons with Late Riphean (peaks on relative probability plots – 0.78, 0.82, 0.94, 1.04 Ga) and Early Riphean (peaks on relative probability plots – 1.38, 1.45, 1.64 Ga) ages predominate. The single grains have a Middle Riphean, Early Proterozoic and Late Archean ages. We can suppose, that the sources of Late Riphean detrital zircons from sandstones of the Chergilen and Allin formations are igneous rocks of gabbro-granitoids (940–933 Ma) and granite- leucogranites (804–789 Ma) association, identified in the Bureya continental Massif. We can`t assume, what kind of rocks were the source for Middle Riphean and older detrital zircons from the Cambrian sedimentary rocks of the Bureya continental Massif, because in this massif still do not identified complexes older Late Riphean age. The most probable geodynamic conditions of accumulation of the Cambrian deposits of the Mel’gin trough is the conditions of active continental margin, which is corresponding to of Early Cambrian granitoids magmatism.
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MA, XIAO, KUNGUANG YANG, and ALI POLAT. "U–Pb ages and Hf isotopes of detrital zircons from pre-Devonian sequences along the southeast Yangtze: a link to the final assembly of East Gondwana." Geological Magazine 156, no. 06 (August 22, 2018): 950–68. http://dx.doi.org/10.1017/s0016756818000511.
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AbstractThe Early Palaeozoic geology of the South China Craton (SCC) is characterized by an Early Palaeozoic intracontinental orogen with folded pre-Devonian strata and migmatites, MP/MT metamorphic rocks and Silurian post-orogenic peraluminous magmatic rocks in both the Yangtze and the Cathaysia blocks. In this contribution, we present new zircon U–Pb ages and Hf isotope data for detrital zircons from the Neoproterozoic to Silurian sedimentary sequences in the southeastern Yangtze Block. Samples from Neoproterozoic rocks generally display a major peak at 900–560 Ma, whereas samples from Lower Palaeozoic rocks are characterized by several broader peaks within the age ranges 600–410 Ma, 1100–780 Ma, 1.6–1.2 Ga and 2.8–2.5 Ga. Provenance analysis indicates that the 900–630 Ma detritus in Cryogenian to Ediacaran samples was derived from the Late Neoproterozoic igneous rocks in South China that acted as an internal source. The occurrence of 620–560 Ma detritus indicates the SE Yangtze was associated with Late Neoproterozoic arc volcanism along the north margin of East Gondwana. The change of provenance resulted in the deposition of 550–520 Ma and 1.1–0.9 Ga detrital zircons in the Cambrian–Ordovician sedimentary rocks. The εHf(t) values of these detrital zircons are similar to those of zircons from NW Australia–Antarctica and South India. This change of provenance in the Cambrian can be attributed to the intracontinental subduction between South China and South Qiangtang, and the convergence of India and Australia when East Gondwana finally amalgamated.
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YAO, WEI-HUA, ZHENG-XIANG LI, and WU-XIAN LI. "Was there a Cambrian ocean in South China? – Insight from detrital provenance analyses." Geological Magazine 152, no. 1 (July 18, 2014): 184–91. http://dx.doi.org/10.1017/s0016756814000338.
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AbstractWe use detrital provenance data from Cambrian sandstones to examine whether the Yangtze and Cathaysia blocks in South China were separated by an ocean during the Cambrian period. Zircons from the Cambrian sandstones exhibit a dominant ~ 800 Ma age peak in the central Yangtze Block, being sourced from the western Yangtze Block, whereas a ~ 980 Ma peak dominates in the northwestern Cathaysia Block, being sourced from an exotic continent once connected to Cathaysia. A mixed provenance with both age peaks is found in Cambrian sandstones from the southeastern Yangtze Block, indicating that detritus can travel from the Cathaysia Block to the Yangtze Block, and therefore arguing against the existence of a broad Cambrian ocean.
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Wang, Yanpeng, Wentao Yang, Shenyuan Peng, Shuaishuai Qi, and Deshun Zheng. "Early Triassic Conversion from Source to Sink on the Southern Margin of the North China Craton: Constraints by Detrital Zircon U-Pb Ages." Minerals 10, no. 1 (December 19, 2019): 7. http://dx.doi.org/10.3390/min10010007.
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Provenance analysis of sediments provides important constraints on basin formation and orogenic processes. With the aim to define the sedimentary provenance and tectonic evolution of the southern margin of the North China Craton, this paper presents new detrital zircon U-Pb data from Early Triassic sediments in the Yiyang area. The results showed major peaks at 1848, 458, 425, and 268 Ma and subordinate peaks at ca. 2500, 872, and 957 Ma on age spectra from the Liujiagou Formation. The Heshanggou Formation exhibited a major age peak at 445 Ma and subordinate peaks at 755 and 947 Ma. Integrated with the analysis of sandstone detrital compositions, we suggest that the sources of the Liujiagou Formation were mainly a mixture of the southern margin of the North China Craton and the North Qinling Orogenic Belt, whereas the Heshanggou Formation was derived primarily from the North Qinling Orogenic Belt. Age comparisons of detrital zircon geochronology collected from different basins in the North China Craton indicated that the paleogeography of the North China Craton during the Early Triassic was strongly asymmetric, wherein the uplifted highland along the southern margin of the North China Craton was relatively lower than the northern margin. Meanwhile, the marked shift in source region from the Liujiagou to the Heshanggou formations provides a constraint regarding the conversion from denuded zone to deposited zone along the southern margin of the North China Craton in the Early Triassic, which controlled the evolution of the provenance and sedimentary system.
Dissertations / Theses on the topic "Detrital peaks"
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Amarasinghe, Udeni Bandara. "A geochronological U-Pb zircon La-ICPMS age and provenance study of Wanni, Highland and Vijayan Complexes of Sri Lanka and Proterozoic Pranhita Godavari Purana Basin of India unveils origin of Sri Lanka." Thesis, 2017. http://hdl.handle.net/2440/113324.
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The island of Sri Lanka is the focus of Neoproterozoic super continent Gondwana. But the geological origin and paleotectonic position of Sri Lanka are least understood without knowing age and provenance of the four main crustal units, the Wanni Complex (WC), Highland Complex (HC), Vijayan Complex (VC) and the Kadugannawa Complex (KC). The study of age and provenance of metaquartzites of the WC and HC, leucosomes and paleosomes of migmatites of the WC, and charnockites of the HC and VC of Sri Lanka and sedimentary rocks of neighboring Proterozoic rift basins like Pranhita-Godavari basin of central India is significant in research on origin of Sri Lanka and also continental evolution to unravel the paleotectonic position of Sri Lanka before Gondwana being amalgamated in the Neoproterozoic. This study examined age of detrital zircon cores and metamorphic rims of metaquartzite, migmatite and charnockite samples along two west to east transects across the island of Sri Lanka as well as sedimentary rock samples from the Pranhita-Godavari rift basin of India using the LA-ICPMS method. The U-Pb zircon isotopic data from metaquartzites of WC ( near WC-HC boundary) and HC demonstrate dominant Mesoarchaean to Paleoproterozoic (2.0-2.8 Ga) detrital input into the metasedimentary make up and near boundary WC and HC metaquartzites were deposited between 2000 Ma and ~550 Ma with a maximum age of deposition ~ 2000 Ma, however a sample from the western WC was deposited in early Neoproterozpoic and mixed with Paleoproterozoic to Neoarchaean detritus indicating WC and HC terranes existed adjacent to each other since early Neoproterozoic and current WC-HC boundary is inaccurate and to be shifted westwards. This study reveals that parent materials of leucosomes of WC migmatitic gneisses are metasedimentary and showing late Mesoproterozoic to Neoproterozoic provenance (0.70-1.15 Ga) with maximum age of deposition at ~700 Ma. But paleosomes of WC migmatites show metaigneous origin with older Mesoarchaean ages (2.85-3.0 Ga) and have been identified in this study as the Mesoarchaean reworked continental basement material of WC. The HC charnockites clearly show metaigneous origin and primary intrusion ages of ~1.82 to 1.85 Ga. whilst a sample from the VC shows metasedimentary origin. A weighted mean of all rim data of WC and HC yields an age of 545.1 ± 9.7 Ma, supporting the age of Ediacaran-Cambrian metamorphism. Metaquartzite rocks of the HC of Sri Lanka are correlated with the Trivandrum Block and Northern Madurai Block of South India and the Itremo Group of Madagascar whilst metaquartzites of the western WC of Sri Lanka are correlated with the Southern Madurai Block of South India and the Molo Group of Madagascar and Sri Lankan metaquartzites were most probably sourced from east African igneous protolith sources. These differences in sedimentary provenance and maximum age of deposition prove and confirm that WC was a different crustal domain from the HC terrane. All this strongly supports a double subduction and collisional geological origin for the island of Sri Lanka with ‘HC orogeny’ occurred when the Southern Madurai Block of India (SMB)-WC and VC Mesoarchaean continental blocks collided with the HC orogenic belt and the oceanic crust of deeper basin of HC had subducted underneath the SMB-WC and VC continental blocks when ancient south Mozambique ocean closed along WC-HC boundary and HC-VC boundary sutures. This study reveals that Sri Lanka’s paleotectonic position could be south east of south India connecting Trivandrum Block to the HC and WC to the Southern Madurai Block. The study also reveals that the Pranhita-Godavari Basin was sourced from Eastern Ghats and Antarctica unlike Sri Lankan terranes were sourced from East Africa indicating Southern Granulite Terrane of India and Sri Lanka were not parts of mainland cratonic India until Ediacaran-Cambrian times.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Physical Sciences, 2017.
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Wulf, Tracy David. "Sequence Stratigraphy and Detrital Zircon Geochronology of the Swan Peak Quartzite, Southeastern Idaho." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10492.
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The supermature Middle-Late Ordovician Swan Peak quartz arenite was deposited on the western Laurentia passive margin and is very fine to fine grained, well-rounded, well-sorted, and silica-cemented. Laurentia was positioned over the equator during the Middle-Late Ordovician, suggesting that basement rock along the Transcontinental Arch was intensely eroded in a humid climate to produce this and other coeval quartz arenites. To determine provenance for the Swan Peak Quartzite, zircon grains were analyzed using LA-ICP-MS and the results were constrained within a sequence stratigraphic framework. Depositional environments of the Swan Peak Quartzite record an offshore-to-onshore transition with five facies (A-E). Facies A only occurs at the base of the Bear Lake section and may record an incised valley or localized embayment. It is the deepest water facies in the succession containing shale and quartz arenite interbeds. Facies B through E are interpreted as lower, middle, upper shoreface/foreshore depositional environments, respectively, based on primary sedimentary structures and bioturbation. Detrital zircon age spectra of the Swan Peak Quartzite have four distinct populations: the two main populations are at 1.8 - 2.0 Ga (Paleoproterozoic) and between 2.5 - 3.0 Ga (Archean), with a smaller, but persistent, population at 2.0 - 2.1 Ga, and a very minor 0.8 - 1.2 Ga (Mesoproterozoic) population occurring mainly in the tops of the measured sections. The base of each section has a larger Archean peak whereas the top of each section is predominantly Paleoproterozoic grains. Zircon data have overlap and similarity values ranging between 0.531 - 0.771 and 0.506 - 0.881, respectively, which indicates zircon age spectra of the Swan Peak Quartzite is similar to other Cordilleran Ordovician quartzites and that recycling of heterogeneous underlying sedimentary rocks was minimal. The Wyoming Craton (2.5 - 2.8 Ga) and the Trans-Hudson Orogen (1.8 - 2.0 Ga) provinces near the paleoequator likely provided the majority of zircons in the Swan Peak Quartzite. The source for the 2.0 - 2.1 Ga grains is currently unknown and the 0.8 - 1.2 Ga grains are interpreted to reflect Mesoproterozoic Laurentian tectonism. Sediment input varied in response to sea level fluctuations. Longshore transport was likely an important process in redistributing grains along the coastline during later deposition of the Swan Peak Quartzite.
Books on the topic "Detrital peaks"
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U-Pb Detrital zircon geochronology results for the Casto Canyon and Wilson Peak quadrangles, Utah. Utah Geological Survey, 2013. http://dx.doi.org/10.34191/ofr-620.
Full textBook chapters on the topic "Detrital peaks"
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Beltrán-Triviño*, Alejandro, Uwe C. Martens, and Albrecht von Quadt. "Siliciclastic provenance of the Cenozoic stratigraphic succession in the southern Gulf of Mexico: Insights from U-Pb detrital zircon geochronology and heavy minerals analysis." In Southern and Central Mexico: Basement Framework, Tectonic Evolution, and Provenance of Mesozoic–Cenozoic Basins, 217–50. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.2546(09).
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ABSTRACT This work presents new geochronological and mineralogical data to investigate the provenance of sediments accumulated in deep-water environments in the southern and southwestern regions of the Gulf of Mexico during the Cenozoic. We integrated U-Pb geochronology with heavy and light minerals data to better understand the provenance of the Paleocene–Miocene strata and the evolution of the sediment source terranes. The analyzed samples came from drill cuttings of sandy levels in five exploration wells offshore in the Gulf of Mexico: Puskon-1, Aktum-1, Kunah-1, Kabilil-1, and Chuktah-201. The material contained abundant barite, a component of the drilling mud. Consequently, a semiquantitative approach to discriminate mineral phases and to quantify concentrations was used. Overall, we recognized 10 zircon populations that range from Proterozoic to Cenozoic ages. Proterozoic ages show a prominent peak at ca. 1.0 Ga and a minor peak at ca. 1.8 Ga. The Neoproterozoic to Cambrian population displays a broad distribution with a peak at ca. 600 Ma. Ordovician–Silurian zircons exhibit minor peaks at ca. 460 and 445 Ma. Devonian and Carboniferous zircons are very scarce in our data set. Permian–Triassic zircons are abundant, and they show a prominent peak at ca. 255 Ma and a minor one at ca. 228 Ma. Jurassic zircons are not common and display several minor peaks at ca. 185, 170, and 155 Ma. The Early Cretaceous population displays a noticeable peak at ca. 120 Ma. Late Cretaceous–Paleocene zircons exhibit several peaks at ca. 92, 82, 72, and 65 Ma. Cenozoic zircons also display several prominent peaks at ca. 40, 35, 25, and 18 Ma. Zircons of Proterozoic to Early Cretaceous ages are interpreted to be derived from the Mesozoic sedimentary cover of basement blocks in southern and eastern Mexico terranes due to their rounded to subrounded morphology. Late Cretaceous and Cenozoic zircons are the most abundant populations in the analyzed samples. These zircon populations exhibit euhedral and subhedral morphology indicating derivation from primary sources in the magmatic arcs. This has important implications in assessing the reservoir quality, since the sediments were directly delivered from the magmatic arc into the deep-water environments. Our results allow us to conclude that the sedimentary provenance of the southwestern and southern strata in the Gulf of Mexico was not associated with Laurentian terranes, as has been proposed for Late Cretaceous–Paleogene strata of northern Mexico and the northern Gulf of Mexico, such as the world-class Wilcox-type hydrocarbon reservoirs. We propose that the provenance of the analyzed strata was related to the tectono-magmatic evolution of the southern Mexico terranes during the Cenozoic; therefore, large NW-SE dispersal systems that eroded Laurentian terranes in the southern United States did not deliver sediments into the southern sectors of the Gulf of Mexico, probably constrained by the Tamaulipas Arch and the Gulf Stream.
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Severson, Allison R., Yvette D. Kuiper, G. Nelson Eby, Hao-Yang Lee, and J. Christopher Hepburn. "New detrital zircon U-Pb ages and Lu-Hf isotopic data from metasedimentary rocks along the western boundary of the composite Avalon terrane in the southeastern New England Appalachians." In New Developments in the Appalachian-Caledonian- Variscan Orogen. Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2554(04).
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ABSTRACT West Avalonia is a composite terrane that rifted from the supercontinent Gondwana in the Ordovician and accreted to Laurentia during the latest Silurian to Devonian Acadian orogeny. The nature and extent of West Avalonia are well constrained in Nova Scotia, New Brunswick, and Newfoundland, Canada, by U-Pb detrital zircon data and/ or isotope geochemistry of (meta)sedimentary and igneous rocks. The southeastern New England Avalon terrane in eastern Massachusetts, Connecticut, and Rhode Island has generally been interpreted as an along-strike continuance of West Avalonia in Canada, but the ages and origins of metasedimentary units along the western boundary of the Avalon terrane in Massachusetts and Connecticut remain poorly constrained. In this study, new detrital zircon U-Pb and Lu-Hf laser-ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) data from three samples of metasedimentary units along the western boundary of the southeastern New England Avalon terrane in Connecticut and Massachusetts were compared with existing data to test whether these metasedimentary units can be correlated along strike. The data were also compared with existing detrital zircon U-Pb and εHf data in New England and Canada in order to constrain the extent and provenance of West Avalonia. The maximum depositional age of two of the three detrital zircon samples analyzed in this study, based on the youngest single grain in each sample (600 ± 28 Ma, n = 1; 617 ± 28 Ma, n = 1) and consistency with existing analyses elsewhere in the southeastern New England Avalon terrane, is Ediacaran, while that of the third sample is Tonian (959 ± 40 Ma, n = 4). Detrital zircon analyses of all three samples from this study showed similar substantial Mesoproterozoic and lesser Paleoproterozoic and Archean populations. Other existing detrital zircon U-Pb data from quartzites in the southeastern New England Avalon terrane show similar Tonian populations with or without Ediacaran grains or populations. Most published detrital zircon U-Pb data from (meta)sedimentary rocks in West Avalonia in Canada yielded Ediacaran youngest detrital zircon age populations, except for a quartzite unit within the Gamble Brook Formation in the Cobequid Highlands of Nova Scotia, which showed a Tonian maximum depositional age, and otherwise a nearly identical detrital zircon signature with rocks from the southeastern New England Avalon terrane. All samples compiled from the southeastern New England Avalon terrane and West Avalonia in Canada show main age populations between ca. 2.0 Ga and ca. 1.0 Ga, with major peaks at ca. 1.95, ca. 1.50, ca. 1.20, and ca. 1.00 Ga, and minor ca. 3.1–3.0 Ga and ca. 2.8–2.6 Ga populations. The εHf(t) values from the three samples yielded similar results to those from West Avalonia in Canada, suggesting that both regions were derived from the same cratonic sources. The εHf(t) values of all West Avalonian samples overlap with both Amazonia and Baltica, suggesting that there is a mixed signature between cratonic sources, possibly as a result of previous collision and transfer of basement fragments between these cratons during the formation of supercontinent Rodinia, or during subsequent arc collisions.
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Sharman, Glenn R., Daniel F. Stockli, Peter Flaig, Robert G. Raynolds, Marieke Dechesne, and Jacob A. Covault. "Tectonic influence on axial-transverse sediment routing in the Denver Basin." In Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2555(11).
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ABSTRACT Detrital zircon U-Pb and (U-Th)/He ages from latest Cretaceous–Eocene strata of the Denver Basin provide novel insights into evolving sediment sourcing, recycling, and dispersal patterns during deposition in an intracontinental foreland basin. In total, 2464 U-Pb and 78 (U-Th)/He analyses of detrital zircons from 21 sandstone samples are presented from outcrop and drill core in the proximal and distal portions of the Denver Basin. Upper Cretaceous samples that predate uplift of the southern Front Range during the Laramide orogeny (Pierre Shale, Fox Hills Sandstone, and Laramie Formation) contain prominent Late Cretaceous (84–77 Ma), Jurassic (169–163 Ma), and Proterozoic (1.69–1.68 Ga) U-Pb ages, along with less abundant Paleozoic through Archean zircon grain ages. These grain ages are consistent with sources in the western U.S. Cordillera, including the Mesozoic Cordilleran magmatic arc and Yavapai-Mazatzal basement, with lesser contributions of Grenville and Appalachian zircon recycled from older sedimentary sequences. Mesozoic zircon (U-Th)/He ages confirm Cordilleran sources and/or recycling from the Sevier orogenic hinterland. Five of the 11 samples from syn-Laramide basin fill (latest Cretaceous–Paleocene D1 Sequence) and all five samples from the overlying Eocene D2 Sequence are dominated by 1.1–1.05 Ga zircon ages that are interpreted to reflect local derivation from the ca. 1.1 Ga Pikes Peak batholith. Corresponding late Mesoproterozoic to early Neoproterozoic zircon (U-Th)/He ages are consistent with local sourcing from the southern Front Range that underwent limited Mesozoic–Cenozoic unroofing. The other six samples from the D1 Sequence yielded detrital zircon U-Pb ages similar to pre-Laramide units, with major U-Pb age peaks at ca. 1.7 and 1.4 Ga but lacking the 1.1 Ga age peak found in the other syn-Laramide samples. One of these samples yielded abundant Mesozoic and Paleozoic (U-Th)/He ages, including prominent Early and Late Cretaceous peaks. We propose that fill of the Denver Basin represents the interplay between locally derived sediment delivered by transverse drainages that emanated from the southern Front Range and a previously unrecognized, possibly extraregional, axial-fluvial system. Transverse alluvial-fluvial fans, preserved in proximal basin fill, record progressive unroofing of southern Front Range basement during D1 and D2 Sequence deposition. Deposits of the upper and lower D1 Sequence across the basin were derived from these fans that emanated from the southern Front Range. However, the finer-grained, middle portion of the D1 Sequence that spans the Cretaceous-Paleogene boundary was deposited by both transverse (proximal basin fill) and axial (distal basin fill) fluvial systems that exhibit contrasting provenance signatures. Although both tectonic and climatic controls likely influenced the stratigraphic development of the Denver Basin, the migration of locally derived fans toward and then away from the thrust front suggests that uplift of the southern Front Range may have peaked at approximately the Cretaceous-Paleogene boundary.
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Daniel, Christopher G., Aphrodite Indares, L. Gordon Medaris, Ruth Aronoff, David Malone, and Joshua Schwartz. "Linking the Pinware, Baraboo, and Picuris orogens: Recognition of a trans-Laurentian ca. 1520–1340 Ma orogenic belt." In Laurentia: Turning Points in the Evolution of a Continent. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.1220(11).
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ABSTRACT It is proposed that the Pinware orogen of eastern Canada, the Baraboo orogen of the midcontinent, and the Picuris orogen of the southwestern United States delineate a previously unrecognized, ~5000-km-long, ca. 1520–1340 Ma trans-Laurentian orogenic belt. All three orogenic provinces are characterized by Mesoproterozoic sedimentation, magmatism, metamorphism, and deformation—the hallmarks of a tectonically active plate margin. Tectonism was diachronous, with the earliest stages beginning ca. 1520 Ma in eastern Canada and ca. 1500 Ma in the southwest United States. Magmatic zircon age distributions are dominated by Mesoproterozoic, unimodal to multimodal age peaks between ca. 1500 and 1340 Ma. The onset of magmatism in the Pinware and Baraboo orogens was ca. 1520 Ma, and onset for the Picuris orogen was ca. 1485 Ma. Detrital zircon age distributions within each orogenic province yield maximum depositional ages between ca. 1570 and 1450 Ma. Minimum depositional ages generally fall between ca. 1500 and 1435 Ma, as constrained by crosscutting intrusions, metatuff layers, or the age of subsequent metamorphism. Metamorphic mineral growth ages from zircon, garnet, and monazite yield peak ages between ca. 1500 and 1350 Ma and tend to be older in the Pinware and Baraboo orogens than in the Picuris orogen. The 40Ar/39Ar cooling ages for hornblende, muscovite, and biotite yield significant peak ages between ca. 1500 and 1350 Ma in the Baraboo and Picuris orogens. We propose that the Pinware-Baraboo-Picuris orogen formed in a complex, diachronous, convergent margin setting along the southern edge of Laurentia from ca. 1520 to 1340 Ma.
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Emery, K. O., and David Neev. "Climate Inferred from Geology and Archaeology." In The Destruction of Sodom, Gomorrah, and Jericho. Oxford University Press, 1995. http://dx.doi.org/10.1093/oso/9780195090949.003.0006.
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Early climatic interpretations for the Lisan and later formations (Late Pleistocene and Holocene—Neev and Emery, 1967, figs. 16, 17) were supported and updated by information from additional coreholes. Although most new and old coreholes bottomed at relatively shallow depths, 20 to 30 m, four of them reached greater depths, 74, 80, 161, and 285 m beneath the 1960 floor of the Dead Sea south basin. The sequences consist of alternating layers of marl and rocksalt. Most marls were deposited from dilute brine during high lake levels and contain alternating laminae of chemical deposits of white aragonite, gray gypsum, and fine-grained detritus consisting of yellowish, brown, green, or dark gray carbonates, quartz, and clay. The detrital fraction is coarser and more dominant toward the deltas, especially near Amazyahu escarpment in the south. Rocksalt layers indicate deposition from more concentrated brine when the levels dropped to about -400 m m.s.l. Lower elevations could have been reached when the sea continued to shrink and when the runoff-to-evaporation ratio diminished, bringing the south basin to complete dessication. As neither the geochemical nature (ionic ratios) of the brines nor the physiography of the terminal water body has changed at least since Late Pleistocene or Lisan Lake time (Katz, Kolodny, and Nissenbaum, 1977), it is probable that through the past 60,000 years rocksalt was precipitated only when the water surface was at or below the critical level of -400 m m.s.l. Gamma-ray logs for some of the new coreholes provide more objective and precise depths of marl and rocksalt layers than do actual samples of sediments. Content of radiogenic minerals in the rocksalt is negligible compared with that in the marl; thus, these layers identify changing physical environments and climates as well as correlating stratigraphy. On gamma-ray logs the peaks or highest intensities of positive anomalies indicate that marl layers or wet climatic subphases and their thicknesses on the logs are proportional to their duration. Presence of negative anomalies or very low levels of gamma radiation show both the existence and thickness of rocksalt layers that denote dry climatic phases.
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Miller, Elizabeth L., Mark E. Raftrey, and Jens-Erik Lund Snee. "Downhill from Austin and Ely to Las Vegas: U-Pb detrital zircon suites from the Eocene–Oligocene Titus Canyon Formation and associated strata, Death Valley, California." In Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2555(14).
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ABSTRACT In a reconnaissance investigation aimed at interrogating the changing topography and paleogeography of the western United States prior to Basin and Range faulting, a preliminary study made use of U-Pb ages of detrital zircon suites from 16 samples from the Eocene–Oligocene Titus Canyon Formation, its overlying units, and correlatives near Death Valley. The Titus Canyon Formation unconformably overlies Neoproterozoic to Devonian strata in the Funeral and Grapevine Mountains of California and Nevada. Samples were collected from (1) the type area in Titus Canyon, (2) the headwaters of Monarch Canyon, and (3) unnamed Cenozoic strata exposed in a klippe of the Boundary Canyon fault in the central Funeral Mountains. Red beds and conglomerates at the base of the Titus Canyon Formation at locations 1 and 2, which contain previously reported 38–37 Ma fossils, yielded mostly Sierran batholith–age detrital zircons (defined by Triassic, Jurassic, and Cretaceous peaks). Overlying channelized fluvial sandstones, conglomerates, and minor lacustrine shale, marl, and limestone record an abrupt change in source region around 38–36 Ma or slightly later, from more local, Sierran arc–derived sediment to extraregional sources to the north. Clasts of red radiolarian-bearing chert, dark radiolarian chert, and quartzite indicate sources in the region of the Golconda and Roberts Mountains allochthons of northern Nevada. Sandstones intercalated with conglomerate contain increasing proportions of Cenozoic zircon sourced from south-migrating, caldera-forming eruptions at the latitude of Austin and Ely in Nevada with maximum depositional ages (MDAs) ranging from 36 to 24 Ma at the top of the Titus Canyon Formation. Carbonate clasts and ash-rich horizons become more prevalent in the overlying conglomeratic Panuga Formation (which contains a previously dated 15.7 Ma ash-flow tuff). The base of the higher, ash-dominated Wahguyhe Formation yielded a MDA of 14.4 Ma. The central Funeral Mountains section exposes a different sequence of units that, based on new data, are correlative to the Titus Canyon, Panuga, and Wahguyhe Formations at locations 1 and 2. An ash-flow tuff above its (unexposed) base provided a MDA of 34 Ma, and the youngest sample yielded a MDA of 12.7 Ma. The striking differences between age-correlative sections, together with map-based evidence for channelization, indicate that the Titus Canyon Formation and overlying units likely represent fluvial channel, floodplain, and lacustrine deposits as sediments mostly bypassed the region, moving south toward the Paleogene shoreline in the Mojave Desert. The profound changes in source regions and sedimentary facies documented in the Titus Canyon Formation took place during ignimbrite flareup magmatism and a proposed eastward shift of the continental divide from the axis of the Cretaceous arc to a new divide in central Nevada in response to thermal uplift and addition of magma to the crust. This uplift initiated south-flowing fluvial systems that supplied sediments to the Titus Canyon Formation and higher units.
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Accotto, Cristina, David Martínez Poyatos, Antonio Azor, Cristina Talavera, Noreen Joyce Evans, Antonio Jabaloy-Sánchez, Hassan El Hadi, and Abdelfatah Tahiri. "Detrital zircon sources in the Ordovician metasedimentary rocks of the Moroccan Meseta: Inferences for northern Gondwanan passive-margin paleogeography." In New Developments in the Appalachian-Caledonian- Variscan Orogen. Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2554(17).
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ABSTRACT Detrital zircon U-Pb geochronology has been widely used to constrain the pre-Carboniferous geography of the European and, to a lesser extent, the Moroccan Variscides. The latter have been generally considered as part of a long-lasting passive margin that characterized northern Gondwana from Ordovician to Devonian time, and was subsequently involved in the late Paleozoic Variscan orogeny. We report detrital zircon ages for three Early to Late Ordovician samples from the Beni Mellala inlier in the northeastern part of the Western Moroccan Meseta in order to discuss the temporal evolution of the sources of sediments in this region. The detrital zircon spectra of these samples, characterized by two main populations with mean ages of 630–610 Ma and 2170–2060 Ma, are typical of Cambrian–Devonian rocks from the Moroccan Variscides and confirm their link to the West African craton. A minor Stenian–Tonian population (peak at ca. 970 Ma) suggests the influence of a distant and intermittent NE African source (Sahara metacraton), which was probably interrupted after Ordovician time. Our data support previous interpretations of the Moroccan Meseta (and the entire northern Moroccan Variscides) as part of the northern Gondwana passive margin. The main sources of these sediments would have been the West African craton in the western regions of the passive margin (Moroc- can Meseta and central European Paleozoic massifs), and the Arabian-Nubian Shield and/or Sahara metacraton in the eastern areas (Libya, Egypt, Jordan, central and NW Iberian zones during Paleozoic time), where the 1.0 Ga detrital zircon population is persistent throughout the Ordovician–Devonian time span.
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Malone, David H., John P. Craddock, and Alexandros Konstantinou. "Timing and structural evolution of the Sevier thrust belt, western Wyoming." In Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.2555(04).
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ABSTRACT The results of new detrital zircon analyses of 15 (n = 1334) Sevier belt synorogenic (Jurassic–Eocene) conglomerates combined with U-Pb zircon ages from the literature (n = 2638) support the structurally dynamic role of the western Paris thrust sheet as the dominant high-standing, out-of-sequence portion of the Sevier belt. This result requires modification of the traditional structural view of the thin-skinned Sevier fold-and-thrust belt having formed by west-to-east shortening over an ~100-m.y. period (ca. 150–50 Ma) with episodic thrust motions that become younger toward the craton (east), as constrained by numerous synorogenic deposits shed to the east from each thrust hanging wall. Sevier thrusting was preceded by deposition of the Jurassic Stump Formation, which has a maximum depositional age of 149 Ma and a unique detrital zircon and heavy mineral (garnet, magnetite) provenance. The oldest thrust, the Paris (Willard) thrust, eroded and deposited the Jurassic–Cretaceous Ephraim Conglomerate as a synorogenic fan devoid of quartzite clasts and with a detrital zircon provenance consistent with reworked sediment from the fold belt, but not from the hinterland or the Sierra Nevada arc of the orogenic system. All subsequent synorogenic deposits from the mid-Cretaceous Echo Conglomerate (Meade-Crawford thrust) to a variety of more easterly Eocene deposits (Sevier belt, Green River, Absaroka, and Bighorn basins) are rich in quartzite clasts. All the quartzite clasts were eroded from the Paris thrust hanging wall, which reached its peak orogenic height at ca. 95 Ma, 50 m.y. after first motion, and the Proterozoic Brigham Group remained a quartzite clast source for ~40 m.y. The detrital zircon signatures of these samples require additional sources of sediment, reworked from the hinterland and the Sierra Nevada and Idaho Batholith arcs, thus implying that long-distance sediment fairway(s) were active during the Mesozoic–early Cenozoic. Based on the same detrital zircon data, variable sources of sediment are inferred between each of the thrust sheets; however, within each thrust system, the source of sediment remained the same. The Teton Range was thrust up at ca. 50 Ma, long after the Sevier belt formed, and it was not a buttress to thin-skinned Sevier deformation. Rather, Teton–Gros Ventre–Wind River Laramide uplifts deformed the older Sevier belt with numerous back and out-of-sequence thrusts and synorogenic deposits, including the Darby thrust, which records the youngest displacement.
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Gottlieb, Eric S., Elizabeth L. Miller, John W. Valley, Christopher M. Fisher, Jeffrey D. Vervoort, and Kouki Kitajima. "Zircon petrochronology of Cretaceous Cordilleran interior granites of the Snake Range and Kern Mountains, Nevada, USA." In Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.2555(02).
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ABSTRACT We addressed fundamental questions about the lithology, age, structure, and thermal evolution of the deep crust of the retroarc hinterland of the North American Cordilleran orogen through systematic investigation of zircons from Cretaceous plutons in the Snake Range and Kern Mountains of east-central Nevada. Geochronological (U-Pb) and geochemical (trace element, O and Hf isotopes) characterization of pre- and synmagmatic growth domains of zircons, coupled with traditional petrologic methods (petrography, field relationships, and whole-rock major-element, trace-element, and Sr-Nd and Pb isotope geochemistry), fingerprinted temporal variations in crustal contributions to magmatism. The samples are typical felsic, peraluminous Cordilleran interior granitoids that formed between 102 ± 2 Ma and 71 ± 1 Ma (95% confidence). Over the entire time span of magmatism, 87Sr/86Srinitial, εNd(t), 208Pb/204Pb, and εHf(t) exhibit incrementally more “crustal” ratios. The oldest and youngest samples, respectively, predate and postdate all published timing constraints of Cretaceous peak metamorphism in the region and exhibit the least and most radiogenic whole-rock isotopic results in the study (87Sr/86Srinitial = 0.7071 vs. 0.7222; εNd(t) = −3.4 vs. −18.8; 208Pb/204Pb = 38.8 vs. 40.1). Accordingly, the least intrasample variability of εHf(t), δ18OZrc, and trace-element ratios in magmatic zircon domains is also observed in these oldest and youngest samples, whereas greater intrasample variability is observed in intermediate-age samples that intruded during peak metamorphism. The geochemistry of zircon growth in the intermediate-age samples suggests assimilation of partially molten metasedimentary crust led to increased heterogeneity in their magma chemistry. Interaction of magmas with distinctive crust types is indicated by contrasts between four categories of inherited zircon observed in the studied intrusions: (1) detrital zircon with typical magmatic trace-element ratios; (2) zircon derived from high-grade 1.8–1.6 Ga basement; (3) zircon with anomalously low δ18O of uncertain origin, derived from 1.7/2.45 Ga basement (or detritus derived thereof); and (4) zircon from variably evolved Jurassic–Early Cretaceous deep-seated intrusions. The progression of zircon inheritance patterns, correlated with evolving geochemical signatures, in Late Cretaceous granitic plutons is best explained by early, relatively primitive intrusions and their penecontemporaneously metamorphosed country rock having been tectonically transported cratonward and superposed on older basement, from which the later, more-evolved Tungstonia pluton was generated. This juxtaposition consequentially implies tectonic transport of synorogenic plutonic rocks occurred in the Cordilleran hinterland during the Sevier orogeny as a result of the interplay of retroarc magmatism and convergent margin tectonism.
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Hoiland, C., J. Hourigan, and E. Miller. "Evidence for large departures from lithostatic pressure during Late Cretaceous metamorphism in the northern Snake Range metamorphic core complex, Nevada." In Tectonic Evolution of the Sevier-Laramide Hinterland, Thrust Belt, and Foreland, and Postorogenic Slab Rollback (180–20 Ma). Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2555(07).
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ABSTRACT The highest-grade Barrovian-type metamorphic rocks of the North American Cordillera exposed today are Late Cretaceous in age and found within an orogen-parallel belt of metamorphic core complexes for which the tectonic histories remain controversial. Thermobarometric studies indicate that many of these Late Cretaceous metamorphic assemblages formed at pressures of >8 kbar, conventionally interpreted as >30 km depth by assuming lithostatic conditions. However, in the northern Basin and Range Province, detailed structural reconstructions and a growing body of contradictory geologic data in and around the metamorphic core complexes indicate these metamorphic rocks are unlikely to have ever been buried any deeper than ~15 km depth (~4 kbar, lithostatic). Recent models controversially interpret this discrepancy as the result of “tectonic overpressure,” whereby the high-grade mineral assemblages were formed under superlithostatic conditions without significant tectonic burial. We performed several detailed studies within the Snake Range metamorphic core complex to test the possibility that cryptic structures responsible for additional burial and exhumation might exist, which would refute such a model. Instead, our data highlight the continued discordance between paleodepth and paleopressure and suggest the latter may have reached nearly twice the lithostatic pressure in the Late Cretaceous. First, new detrital zircon U-Pb geochronology combined with finite-strain estimates show that prestrain thicknesses of the lower-plate units that host the high-pressure mineral assemblages correspond closely to the thicknesses of equivalent-age units in adjacent ranges rather than to those of the inferred, structurally overridden (para) autochthon, inconsistent with cross sections and interpretations that assume a lower plate with a deeper origin for these rocks. Second, new Raman spectroscopy of carbonaceous material of upper- and lower-plate units identified an ~200 °C difference in peak metamorphic temperatures across the northern Snake Range detachment but did not identify any intraplate discontinuities, thereby limiting the amount of structural excision to motion on the northern Snake Range detachment itself, and locally, to no more than 7–11 km. Third, mapped geology and field relationships indicate that a pre-Cenozoic fold truncated by the northern Snake Range detachment could have produced ~3–9 km of structural overburden above Precambrian units, on the order of that potentially excised by the northern Snake Range detachment but still far short of expected overburden based on lithostatic assumptions. Fourth, finite-strain measurements indicate a shortening (constrictional) strain regime favorable to superlithostatic conditions. Together, these observations suggest that pressures during peak metamorphism may have locally reached ~150%–200% lithostatic pressure. Such departures from lithostatic conditions are expected to have been most pronounced above regions of high heat flow and partial melting, and/or at the base of regional thrust-bounded allochthons, as is characteristic of the spatial distribution of Cordilleran metamorphic core complexes during the Late Cretaceous Sevier orogeny.
Reports on the topic "Detrital peaks"
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McKean, Adam P., Zachary W. Anderson, Donald L. Clark, Diego Fernandez, Christopher R. Anderson, Tiffany A. Rivera, and Taylor K. McCombs. Detrital Zircon U-Pb Geochronology Results for the Bountiful Peak, Coalville, James Peak, Mount Pisgah, Paradise, and Payson Lakes 7.5' Quadrangles, Utah. Utah Geological Survey, May 2022. http://dx.doi.org/10.34191/ofr-743.
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This Open-File Report makes available raw analytical data from laboratory analysis of U-Pb ages of zircon grains from samples collected during geologic mapping funded by the U.S. Geological Survey (USGS) National Cooperative Geologic Mapping Program (STATEMAP) and the Utah Geological Survey (UGS). The references listed in table 1 provide additional information such as sample location, geologic setting, and interpretation of the samples in the context of the area where they were collected. The data were prepared by the University of Utah Earth Core Facility (Diego Fernandez, Director), under contract to the UGS. These data are highly technical in nature and proper interpretation requires considerable training in the applicable geochronologic techniques.