四川盆地古近系柳嘉组碎屑锆石U-Pb年代学研究及其地质意义

DETRITAL ZIRCON U-PB GEOCHRONOLOGY OF THE LIUJIA FORMATION OF PALEOGENE IN SICHUAN BASIN AND ITS GEOLOGICAL SIGNIFICANCE

四川盆地古近系柳嘉组以发育沙漠沉积为特征,是青藏高原东缘古近纪风成沙丘富集带的重要组成部分。采用碎屑锆石LA-ICP-MS年代学方法,首次研究了柳嘉组碎屑锆石年龄组成,分析了该组的沉积物来源,探讨了物源区区域构造热事件在柳嘉组碎屑锆石年龄谱中的反映。获得的53组碎屑锆石U-Pb有效年龄表明,柳嘉组的物源主要集中在1 811Ma^1 677Ma、865Ma^705Ma、457Ma^384Ma、306Ma^240Ma及218Ma^129Ma五个区间,物源区主要为扬子陆块西缘。综合研究表明,柳嘉组碎屑锆石存在5个较为明显的峰值1 773Ma±82Ma、800Ma±5Ma、298Ma±4Ma、252Ma±3Ma及201Ma±2Ma,记录了扬子陆块西缘古元古代—中生代5次较为重要的构造热事件。

The Paleogene Liujia Formation in Sichuan Basin is characterized by desert sediments and is an important component of the Paleogene aeolian dune accumulation zone along the eastern margin of the Qinghai-Tibet Plateau. The age distribution of the detrital zircons from the Liujia Formation is firstly reported by using detrital zircon LA-ICP-MS U-Pb dating method. Also, the provenance of the Liujia Formation is analyzed and the regional thermo-teetonic event in the prov- enance area recorded in the detrital zircon chronicle of the Liujia Formation is studied. 53 effective detrital zircon U-Pb ages show that the provenance of the Liujia Formation are mostly distributed in five ranges of 1 811 Maul 677 Ma,865 Ma-705 Ma,457 Ma-384 Ma, 306 Ma-240 Ma and 218 Ma-129 Ma,and the main provenance area is located in the western margin of the Yangtze Block. Comprehensive analysis shows that the detrital zircons of the Liujia Formation have five evident peak values of 1 773 Ma±82 Ma,800 Ma±5 Ma,298 Ma±4 Ma,252 Ma±3 Ma and 201 Ma-b2 Ma,representing five relatively important thermo-tectonic events occurred in the western margin of the Yangtze Block from the Palaeoproterozoic to the Mesozoic.