内蒙古苏尼特左旗北奥陶系砂岩物源分析及其地质意义

Provenance analysis of the Ordovician sandstones in northern Sonid Left Banner area of Inner Mongolia and its geological significance

对内蒙古苏尼特左旗北奥陶系砂岩的岩石学和锆石年龄进行研究。镜下特征显示该套砂岩为岩屑砂岩,含有较多的火山岩屑;砂岩颗粒骨架成分图解显示其来自再旋回造山带。应用LA-ICP-MS测年技术对该套砂岩进行碎屑锆石分析,其年龄峰期从小到大可分为：1440～574Ma,主峰值年龄为506Ma,次峰值年龄为442Ma;2650～799Ma,峰值年龄为767Ma;3874～936Ma,峰值年龄为887Ma;另外大于1000Ma的4颗单颗粒锆石年龄分别为1145Ma、1756Ma、2618Ma和2626Ma。通过邻区相关地块/地体年龄及岩浆事件的对比可知,该套砂岩的沉积时间约为440Ma,沉积物源主要来自于额尔古纳地块和兴安地块,并且沉积过程受到火山事件的影响。

The petrology and zircon ages of the Ordovician sandstones in northern Sonid Left Banner area of Inner Mongolia were studied in this paper.The sandstones belong to a kind of lithic sandstone with lots of volcanic debris.The sandstone grain matrix component diagrams show that the sandstones came from the recycled orogenic belts.LA-ICP-MS dating technique was used to make detrital zircon analysis for one sandstone sample,and the age periods obtained are from low to high as follows：1440～574Ma with the major peak at 506 Ma and subordinate peak at 442Ma;2650～799Ma with the peak at 767Ma;3874～936Ma with the peak at887Ma;ages of the other four zircon samples are 1145 Ma,1756 Ma,2618 Ma and 2626 Ma,respectively.Based on the comparison of ages and magmatic events with relative adjacent cratons and/or terrenes,the authors infer that the sandstones formed at 440 Ma,and the provenances were mainly derived from the Erguna and Xing＇an terranes,with the sedimentary process affected by volcanic events.