秦昆结合部塔秀地区隆务河组碎屑锆石LA-ICP-MSU-Pb年代学及其地质意义

秦昆结合部独特的地质组成与复杂的造山带结构受到广泛关注。前人对该地区沉积物质来源进行了初步分析,但存在较大争议。选取隆务河组碎屑岩为研究对象,运用碎屑锆石LA-ICP-MS U-Pb同位素年代学方法,探讨隆务河组物源特征。U-Pb测年结果表明,隆务河组碎屑锆石年龄谱明显分为4组:2 746~2 084 Ma,1 094~775 Ma,492~411 Ma,372~237 Ma。其中,372~237 Ma年龄组约占总体的56.79%,所占比例最大,年龄相对集中,且呈现出强烈的峰值,代表了阿尼玛卿洋向北俯冲碰撞产生的一系列构造岩浆事件,其余年龄段所占比例则较少。综合分析显示,隆务河组碎屑沉积物质来源较为复杂,具有明显的多元性,存在祁连造山带、柴北缘构造带和东昆仑造山带3个物源区,其中东昆仑造山带提供了大部分物源,为隆务河组贡献最大的物源区。

LA-ICP-MS U-Pb Geochronology of Detrital Zircons from the Longwuhe Formation in Taxiu Area,the Junction Area Between the Qinling and Kunlun Orogenic Belts

The junction area between the Qinling and Kunlun orogenic belts has received wide attention for its unique geological compositions and complex orogenic structures. The preliminary analysis has been performed previously on the provenance of sediments in this area but still remained controversy. This paper selects clastic rocks from the Longwuhe Formation and uses LA-ICP-MS U-Pb ages of detrital zircons to restrict their provenance characteristics. Our results show that the zircon U-Pb ages can be divided into four groups, i.e., 2 746-2 084 Ma, 1 094-775 Ma, 492-411 Ma and 372-237 Ma. Among them, the 372-237 Ma group accounts for 56.79% of the total. This largest proportion age group is relatively concentrated with a evident peak, representing a series of tectonic magma events caused by the subduction of the A’nyemaqen ocean. The comprehensive analysis reveals that the sources of clastic sediments in the Longwuhe Formation are complex and diverse, including the northern margin of the Qaidam Basin, the Qilian orogenic belt and the Eastern Kunlun orogenic belt. The Eastern Kunlun orogenic belt is the largest provenance area of the Longwuhe Formation and provides most sedimentary materials.