Provenance and Tectonic Settings of Triassic Xujiahe Formation in Qiyueshan Area,Southwest Hubei:Evidences from Petrology, Geochemistry and Zircon U-Pb Ages of Clastic Rocks
Tian Yang
Xie Guogang
Wang Lingzhan
Tu Bing
Zhao Xiaoming
Zeng Bofu
Abstract：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 Yan-jiagou sections were tested and analyzed.All sandstone samples are rich in quartz (Q),poor in lithic fragments (L)and feld-spar (F),with an average of 76.1 5%,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 (TFe2 O 3 + MgO)* (1.3%,1.5%,average for Zhoujiawan and Yanjiagou sections respectively),low TiO 2 * (0.37%, 0.39%),low Al2 O 3/SiO 2 (0.10,0.12)and high K2 O/Na2 O(4.89,40.01),which are most similar to the characteristics of pas-sive 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 pas-sive and active continental margin settings during Late Triassic.Detrital zircons can be divided into rounded and euhedral cate-gories.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 Yan-gtze craton.Having two prominent age peaks 435 Ma and 21 7 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 discrimi-nation diagrams,these characteristics all above suggest that Xujiahe Formation deposited in passive (main)and active continen-tal margin,and its provenances were from Xuefeng orogenic belt (main source)and Qinling orogen.
Keywords：provenancetectonic settinggeochemistryclastic compositiondetrital zirconXujiahe FormationSouthwest Hubei
Publication Date：2015-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：16( 2031-2046 )