X. Cui, M. Sun, Guochun Zhao, Jinlong Yao, Yunying Zhang, Yigui Han
{"title":"中国阿尔泰南部早古生代活动大陆边缘盆地:来自富云地区高品位副长岩的证据","authors":"X. Cui, M. Sun, Guochun Zhao, Jinlong Yao, Yunying Zhang, Yigui Han","doi":"10.2475/02.2022.04","DOIUrl":null,"url":null,"abstract":"High-grade gneisses are widespread in the Chinese segment of the Altai orogen, but their nature is not yet well-constrained with interpretations varying from Precambrian basement to Paleozoic meta-sediments. Such a controversy has hindered our understanding of the early Paleozoic geologic history of the Altai orogen. This study presents whole-rock geochemistry, zircon U-Pb and Hf isotopic data for paragneisses from the Qiongkuer Domain of the southern Chinese Altai, aiming to reveal their sedimentary and metamorphic history and shed light on the geodynamics of the Altai orogen. The paragneisses contain detrital zircons with mostly euhedral shapes, which, together with their weak HREE fractionation and Zr-Hf depletion relative to continental crust, may imply short-distance transport and low maturity of the sediments. In addition, these rocks have felsic compositions, high Rb contents and negative Eu anomalies, as well as low La/Sc and high Co/Th ratios, possibly indicating an acidic-intermediate igneous provenance. Our results show that the detrital zircons from the paragneisses are dominantly ca. 535 to 435 Ma old, some have Neoproterozoic ages, and only a few have Mesoproterozoic or Archean ages. Since the youngest detrital zircon population record an early Silurian weighted mean age of 441 Ma, and an early Devonian (411 Ma) granite intruded these paragneisses, we infer that their protoliths were deposited in the Silurian. The cumulative distribution curves of zircon age spectra of the paragneisses are comparable to those of sediments at convergent continental margins. The large spread of εHf(t) values (−9.5 to +12.9) of the predominant Paleozoic zircons also reflects possible active margin settings which contain both juvenile and reworked materials in the source. Therefore, the protoliths of the studied paragneisses were immature sediments mostly deposited at an active continental margin during the early Paleozoic and sourced mainly from proximal igneous rocks. Similar detrital zircon age spectra of early Paleozoic sequences from the Chinese Altai, Mongolia Altai, and Khovd Zone support the existence of a large accretionary wedge developed along the western margin of the Ikh-Mongol Arc system, resulting from continuous northeast-dipping oceanic subduction.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"190 - 224"},"PeriodicalIF":1.9000,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"2","resultStr":"{\"title\":\"An early Paleozoic active continental margin basin along the southern Chinese Altai: Evidence from high-grade paragneisses in the Fuyun region\",\"authors\":\"X. Cui, M. Sun, Guochun Zhao, Jinlong Yao, Yunying Zhang, Yigui Han\",\"doi\":\"10.2475/02.2022.04\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"High-grade gneisses are widespread in the Chinese segment of the Altai orogen, but their nature is not yet well-constrained with interpretations varying from Precambrian basement to Paleozoic meta-sediments. Such a controversy has hindered our understanding of the early Paleozoic geologic history of the Altai orogen. This study presents whole-rock geochemistry, zircon U-Pb and Hf isotopic data for paragneisses from the Qiongkuer Domain of the southern Chinese Altai, aiming to reveal their sedimentary and metamorphic history and shed light on the geodynamics of the Altai orogen. The paragneisses contain detrital zircons with mostly euhedral shapes, which, together with their weak HREE fractionation and Zr-Hf depletion relative to continental crust, may imply short-distance transport and low maturity of the sediments. In addition, these rocks have felsic compositions, high Rb contents and negative Eu anomalies, as well as low La/Sc and high Co/Th ratios, possibly indicating an acidic-intermediate igneous provenance. Our results show that the detrital zircons from the paragneisses are dominantly ca. 535 to 435 Ma old, some have Neoproterozoic ages, and only a few have Mesoproterozoic or Archean ages. Since the youngest detrital zircon population record an early Silurian weighted mean age of 441 Ma, and an early Devonian (411 Ma) granite intruded these paragneisses, we infer that their protoliths were deposited in the Silurian. The cumulative distribution curves of zircon age spectra of the paragneisses are comparable to those of sediments at convergent continental margins. The large spread of εHf(t) values (−9.5 to +12.9) of the predominant Paleozoic zircons also reflects possible active margin settings which contain both juvenile and reworked materials in the source. Therefore, the protoliths of the studied paragneisses were immature sediments mostly deposited at an active continental margin during the early Paleozoic and sourced mainly from proximal igneous rocks. 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An early Paleozoic active continental margin basin along the southern Chinese Altai: Evidence from high-grade paragneisses in the Fuyun region
High-grade gneisses are widespread in the Chinese segment of the Altai orogen, but their nature is not yet well-constrained with interpretations varying from Precambrian basement to Paleozoic meta-sediments. Such a controversy has hindered our understanding of the early Paleozoic geologic history of the Altai orogen. This study presents whole-rock geochemistry, zircon U-Pb and Hf isotopic data for paragneisses from the Qiongkuer Domain of the southern Chinese Altai, aiming to reveal their sedimentary and metamorphic history and shed light on the geodynamics of the Altai orogen. The paragneisses contain detrital zircons with mostly euhedral shapes, which, together with their weak HREE fractionation and Zr-Hf depletion relative to continental crust, may imply short-distance transport and low maturity of the sediments. In addition, these rocks have felsic compositions, high Rb contents and negative Eu anomalies, as well as low La/Sc and high Co/Th ratios, possibly indicating an acidic-intermediate igneous provenance. Our results show that the detrital zircons from the paragneisses are dominantly ca. 535 to 435 Ma old, some have Neoproterozoic ages, and only a few have Mesoproterozoic or Archean ages. Since the youngest detrital zircon population record an early Silurian weighted mean age of 441 Ma, and an early Devonian (411 Ma) granite intruded these paragneisses, we infer that their protoliths were deposited in the Silurian. The cumulative distribution curves of zircon age spectra of the paragneisses are comparable to those of sediments at convergent continental margins. The large spread of εHf(t) values (−9.5 to +12.9) of the predominant Paleozoic zircons also reflects possible active margin settings which contain both juvenile and reworked materials in the source. Therefore, the protoliths of the studied paragneisses were immature sediments mostly deposited at an active continental margin during the early Paleozoic and sourced mainly from proximal igneous rocks. Similar detrital zircon age spectra of early Paleozoic sequences from the Chinese Altai, Mongolia Altai, and Khovd Zone support the existence of a large accretionary wedge developed along the western margin of the Ikh-Mongol Arc system, resulting from continuous northeast-dipping oceanic subduction.
期刊介绍:
The American Journal of Science (AJS), founded in 1818 by Benjamin Silliman, is the oldest scientific journal in the United States that has been published continuously. The Journal is devoted to geology and related sciences and publishes articles from around the world presenting results of major research from all earth sciences. Readers are primarily earth scientists in academia and government institutions.