广西西大明山隆起带寒武-泥盆系碎屑锆石年龄谱系及其地质意义

Cambrian-Devonian detrital zircon U-Pb age spectrums and its geological significance for the Xidamingshan uplift zone in Guangxi

广西西大明山地区地处钦-杭缝合带的西南端,是研究华南板块西南缘大地构造演化的关键位置。选取西大明山地区中寒武统黄洞口组和下泥盆统莲花山组中的2件砂岩样品进行碎屑锆石U-Pb年代学测试,结果显示:黄洞口组谐和年龄数据主要集中在550、750、1000、1400~1500、2470~2600 Ma;莲花山组碎屑锆石年龄呈现出3个明显的峰值,为515、750和950 Ma。两者均存有750和950~1000 Ma的主要年龄峰值,其中750 Ma与Rodinia超大陆的裂解事件有关,而950~1000 Ma则反映物源区曾是Grenville期造山带的一部分。将其与扬子地块和华夏地块碎屑锆石年龄谱系进行对比发现,西大明山地区中寒武统黄洞口组和下泥盆统莲花山组都与华夏地块具有亲缘性,推测扬子与华夏地块之间的西南界线应位于西大明山地区以北。

The Xidamingshan district is located at the southwestern Qinzhou-Hangzhou suture zone in Guangxi,a significant region for studying the tectonic evolution of South China.In this paper,detailed LA-ICP-MS zircon U-Pb dating analyses are carried out on the detrital zircons from 2 samples of Huangdongkou Formation of Middle Cambrian Series and Lianhuanshan Formation of Lower Devonian Series sandstone rocks.The age spectra of detrital zircons from the Huangdongkou Formation sample shows the major populations at 550,750,1000,1400-1500,2470-2600 Ma.The Lianhuanshan Formation shows three ranges of 515,750 and 950 Ma.There are similar major peaks at 750 Ma and 950-1000 Ma.Among them the obvious age peak is at 750 Ma,maybe due to Rodinia supercontinent breakup,indicating the product of magmatic activity.The age spectrum of 950-1000 Ma is correlated with the Grenville orogency tectono-thermal events in the provenance.Compared with the zircon U-Pb time spectra of the Yangtze Block and the Cathaysia Block,the detrital zircons in the Huangdongkou Formation and Lianhuanshan Formation sedimentary rocks of the Xidamingshan district were mainly derived from the Cathaysian Block.The southwestern continental boundary between the Yangtze and Cathaysian blocks was located north to the Xidamingshan district.