南秦岭北缘淅川地区泥盆纪地层的物源及构造背景
Provenance and Tectonic Settings of Devonian Sedimentary Strata in Xichuan Area, Northern Margin of South Qinling Block

造山带内广泛发育的泥盆纪地层是揭示秦岭造山带古生代中期洋陆演化、地块构造属性和大地构造背景的良好载体.对南秦岭内部淅川地区泥盆系砂岩进行了岩石地球化学和锆石U-Pb定年，结果显示泥盆系碎屑岩具有中等的成分成熟度及一定程度的沉积再旋回特征，源区物质成分以上地壳长英质岩石为主；碎屑锆石的年龄区间主要集中在新元古代晚期-古生代(0.40～0.63 Ga)、新元古代(0.7～0.9 Ga)和中元古代(1.0～1.6 Ga)三个区间，并存在少量古元古代和中-晚太古代年龄.综合分析，淅川地区泥盆系主要形成于被动大陆边缘环境，其物源可能主要为南秦岭自身隆升的基底和构造高地，并未接受来自于北秦岭的物质，沿商丹洋的俯冲增生事件可能未影响到南秦岭内部.
The Devonian sedimentary strata, widely developed in the Qinling orogenic belt, are good carriers to reveal the ocean continent transition, tectonic attributes and tectonic settings of the Qinling orogenic belt in the Middle Paleozoic. This study presents new geochemical and zircon U-Pb isotopic data for the Devonian sedimentary rocks in Xichuan area. Geochemical data show that the Devonian clastic rocks are characterized by moderate compositional maturity, and a higher portion of sediment recycling, and are likely to have been derived predominantly from felsic igneous rocks within upper-continental-crustal. The detrital zircon ages mainly concentrated in Late Neoproterozoic Paleozoic (0.40-0.63 Ga), Neoproterozoic (0.7-0.9 Ga) and Mesoproterozoic (1.0-1.6 Ga), with a small amount of ages in Paleoproterozoic and Middle Late Archean. Comprehensive analysis suggests that the Devonian basin in Xichuan area formed in passive continental margin, and its provenance may be mainly the uplift basement and tectonic highland of the South Qinling, not from the North Qinling. The subduction accretion event along the Shangdan Ocean probably did not affect the interior of South Qinling