新疆阿尔泰阿勒泰组沉积时代及其形成环境

阿勒泰组变质碎屑岩局部夹变质火山岩广泛分布于南阿尔泰的冲乎尔、克兰和麦兹盆地,其沉积时代和构造环境对于研究阿尔泰造山带的演化过程有重要意义。阿勒泰组碎屑锆石的年代学研究表明,碎唐锆石年龄主要集中在417-383 Ma和507-445 Ma,并出现少量元古宙和太古宙碎屑锆石。少数锆石年龄为380-354 Ma,与阿勒泰组凝灰岩和流纹岩年龄一致(376~354 Ma)。综合研究认为阿勒泰组时代为中-晚泥盆世(382-354 Ma)。阿勒泰组长石石英砂岩分选性和磨圆度较差,为近源沉积,物源岩石主要来自泥盆纪火山岩,其次是晚寒武一早奥陶世火山岩和奥陶纪花岗岩。长石石英砂岩样品具有高的La/Sc(3.9-6.3),La/Y(1.0~1.6),较低的Sc/Cr(0.2~0.4)比值,类似于大陆岛弧相关环境碎屑沉积物,结合Th-Co-Zr/10和Th-Sc-Zr/10以及La-Th-Sc判别图,认为阿勒泰组形成于与岛弧相关的构造环境(弧后盆地),为研究阿尔泰造山带泥盆纪构造演化提供了重要证据。

Constraining the deposition time and sedimentary environments of the Altay Formation in Altay,Xinjiang

The Altay Formation mainly consists of meta-clastic sediments, with minor meta-volcanic rocks, which widely distributed in the Chonghu’er, Kelan and Maizi Basins of South Altay, and can provide important constraints on the tectonic evolution of the Altay orogenic belt（AOB）. The current geochronological study for the detrital zircons of the Altay Formation shows that the ages of them are mainly concentrated in 417～383 Ma and 507～445 Ma, and only rarely are Proterozoic and Archean. Meanwhile, a few zircon ages range from 380～354 Ma, which are consistent with the ages of the Altay Formation tuff and rhyolite（376～354 Ma）. Comprehensive research suggests that the Altay Formation was formed during the Middle-Late Devonian（382～354 Ma）. The feldspar quartz sandstone of the Altay Formation is a near-source sediment with less sorted and poor rounded. The sources of the sandstone are mainly from the Devonian volcanic rocks, followed by the Late Cambrian-Early Ordovician volcanic rocks and Ordovician granites. The feldspar quartz sandstone samples have high La/Sc（3.9～6.3）, La/Y（1.0～1.6）, and low Sc/Cr（0.2～0.4）ratios, which are similar to clastic rocks deposited in continental arc settings. Combined with Th-Co-Zr/10, Th-Sc-Zr/10 and La-Th-Sc discriminate diagrams, it is believed that the Altay Formation was formed in a tectonic setting associated with the island arc（the back-arc basin）, which provides important evidence for studying the Devonian tectonic evolution of the AOB.