鄂西南齐岳山须家河组物源及构造背景:来自岩石学、地球化学和锆石年代学的制约

为揭示鄂西南齐岳山地区晚三叠世须家河组物源与构造背景，以周家湾与颜家沟剖面为代表，对须家河组碎屑岩的颗粒组分、元素组成以及锆石年龄进行测试与统计.结果显示:砂岩碎屑颗粒石英含量高、岩屑与长石含量低，平均值分别为76.15%、8.90%与3.45%，具有锆石-板钛矿-磁铁矿-榍石-电气石重矿物组合，反映源岩以酸性岩或低级变质岩为主，Dickinson判别图解表明物源主要来自再旋回造山带；砂岩(TFe₂O₃+MgO)*与TiO₂*含量低，Al₂O₃/SiO₂比值低，K₂O/Na₂O比值高，最接近被动大陆边缘特征值；泥岩成分变异指数ICV分布于0.32~0.79之间，平均值为0.56，反映物源主要为再旋回沉积物；样品稀土元素配分模式、特征微量元素含量及比值指示晚三叠世沉积构造背景为被动与活动大陆边缘；碎屑锆石分为磨圆与自形两类，磨圆者具有2 480 Ma、1 880 Ma、832 Ma年龄峰值(n=133)，年龄频数分特征与扬子陆块最接近；自形锆石具有435 Ma、217 Ma年龄峰值(n=42)，年龄频数分布特征与秦岭造山带和雪峰造山带花岗岩年龄具有很好的对应关系.结合物源与构造背景判别图解，上述特征综合表明须家河组形成于被动大陆边缘(为主)与活动大陆边缘环境，其物源来自东南的雪峰造山带(为主)与北侧的秦岭造山带. 

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

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.