中祁连党河南山-木里地区早古生代火山-沉积岩系锆石U-Pb年代学、物源示踪及其地质意义SCIEI北大核心CSCD

造山带内与板块俯冲-碰撞过程相关的一系列沉积盆地对于重建造山带演化历史具有重要意义。本文以党河南山-木里地区早古生代火山-沉积岩系为研究对象,对其开展沉积序列、锆石U-Pb年代学、Hf同位素及碎屑物源综合分析,研究结果表明:(1)该火山-沉积岩系从底部吾力沟组到中部盐池湾组,整体上表现为弧后盆地的演化特征,顶部多索曲组具有向前陆盆地演化的特征;(2)获得吾力沟组玄武安山岩锆石U-Pb年龄为472±10Ma,限定盐池湾组和多索曲组沉积时代分别为467~450Ma和450~440Ma;(3)盐池湾组碎屑锆石年龄谱系和锆石ε;(t)组成说明盐池湾组碎屑物质主要来源于中祁连岩浆弧;而多索曲组的早古生代碎屑物质主要来源于伴生的火山岩或南祁连花岗岩,前寒武纪碎屑物质主要来自于中祁连。综合分析与汇聚板块边缘相关的沉积盆地特征和前人研究资料,本文认为党河南山-木里地区的早古生代火山-沉积岩系可能形成于弧后盆地及其闭合过程的前陆盆地环境。

U-Pb geochronology, provenance and geological implications of Early Paleozoic volcano-sedimentary rocks in the Danghenanshan-Muli area, Central Qilian belt

Sedimentary basins related to the processes of plate subduction and collision in orogenic belt play a key role in tectonic reconstruction of the Qilian orogen. Seven samples for laser ablation ICP-MS U-Pb zircon dating were collected from Early Paleozoic volcano-sedimentary rocks in the Danghenanshan-Muli area. Our results indicate that : (1) Volcano-sedimentary sequences from the lower Wuligou Formation to the middle Yanchiwan Formation show characteristics of a backarc basin, while sedimentary rocks of the upper Duosuoqu Formation have characteristics of a foreland basin; (2) Basaltic andesite of the Wuligou Formation was formed at 472 +/- 10Ma, and depositional ages of the Yanchiwan and Duosuoqu formations are ca. 467 similar to 450Ma and 450 similar to 440Ma, respectively; (3) Detrital zircon U-Pb data and epsilon(Hf) (t) values of the Yanchiwan Formation show similar data to arc granitoids of the Central Qilian belt, while those of the Duosuoqu Formation record a source derived from associated volcanic rocks or granitoids of the South Qilian belt and the Precambrian material of the Central Qilian belt. These results suggest that Early Paleozoic volcano-sedimentary rocks in the Danghenanshan-Muli area was likely developed in a backarc basin and a foreland basin formed during the closure of the former.