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Tian Y.,Wuhan Center | Tian Y.,Key Laboratory for Paleontology and Coevolution of Life and Environment | Xie G.,Wuhan Center | Xie G.,Key Laboratory for Paleontology and Coevolution of Life and Environment | And 8 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences

For revealing provenance and tectonic settings of Triassic Xujiahe Formation in Qiyueshan area, Southwest Hubei, detrital compositions, major, trace and rare earth elements, and zircon isotope ages of clastic rocks from Zhoujiawan and Yanjiagou sections were tested and analyzed. All sandstone samples are rich in quartz (Q), poor in lithic fragments (L) and feldspar (F), with an average of 76.15%, 8.90% and 3.45% respectively, Q/(Q+F+L) being averaged at 0.86, featuring with heavy mineral assemblage of zircon-brookite-magnetite-sphene-tourmaline, which suggests an acidic or low-grade metamorphic source. Dickinson discrimination diagrams show provenance mainly from recycled orogen. The sandstones are characterized by low (TFe2O3+MgO)* (1.3%, 1.5%, average for Zhoujiawan and Yanjiagou sections respectively), low TiO2 * (0.37%, 0.39%), low Al2O3/SiO2 (0.10, 0.12) and high K2O/Na2O(4.89, 40.01), which are most similar to the characteristics of passive continental margin. The index of compositional variation (ICV: 0.32~0.79, average: 0.56) for mudstones implies the source materials are mainly recycled sediments. The REE patterns, contents and ratios of specific trace elements indicate passive and active continental margin settings during Late Triassic. Detrital zircons can be divided into rounded and euhedral categories. As recycled zircons mostly, rounded zircons (>500 Ma, n=133) are characterized by “core-edge” or “core-mantle-edge” structure. Three prominent age peaks, i. e. 2 480 Ma, 1 880 Ma and 832 Ma are obtained, suggesting fingerprint of Yangtze craton. Having two prominent age peaks 435 Ma and 217 Ma, cylindrical euhedral zircons (<500 Ma, n=42) with typical oscillatory zoning possess the characteristics of Xuefeng and Qinling orogens. Combined with provenance and tectonic discrimination diagrams, these characteristics all above suggest that Xujiahe Formation deposited in passive (main) and active continental margin, and its provenances were from Xuefeng orogenic belt (main source) and Qinling orogen. © 2015, Editorial Department of Earth Science-Journal of China University of Geosciences. All right reserved. Source

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