大别山东南缘侏罗系磨山组沉积环境及地质意义

侏罗纪是大别造山带与周缘盆地盆山关系研究的一个重要时期,分布在大别造山带周缘的侏罗纪地层为大别山的造山过程以及深俯冲岩石的折返、剥蚀提供了很好的约束。本文选取大别造山带东南缘安庆月山地区侏罗系磨山组为研究对象,对磨山组碎屑岩进行了详细的粒度分析、碎屑组分分析、重矿物分析和碎屑锆石年代学分析。碎屑岩岩石、沉积特征和粒度分析都指示早侏罗世磨山组为三角洲前缘水下分流河道沉积。碎屑组分分析、重矿物分析结合碎屑锆石年代学分析指示磨山组碎屑岩物源主要来自南侧的华南板块,大别造山带宿松杂岩可能为其提供了少量物源,但碎屑物源中未见石榴子石和典型的三叠纪变质锆石,说明此时大别高压-超高压榴辉岩可能仍未折返至地表。

Sedimentary environments and its geological significance of Jurassic Moshan Formation in the northeastern margin of Dabie Mountain

Jurassic is an important period in basin-mountain coupling studies between Dabie orogenic belt and adjacent basins. The Jurassic strata on the periphery of Dabie Mountain provide well constraints on the orogenic processes of Dabie Mountain and the exhumation and uproofing of deep subduction rocks. This paper chooses Jurassic Moshan Formation in Yueshan area of Anqing in the northeastern margin of Dabie Mountain as the study object. Fine analysis of grain size, detrital composition, heavy mineral assemblages and U-Pb isotope chronologic dating of detrital zircons are carried out on clastic rocks of Moshan Formation. The lithological and sedimentary characteristics and result of grain size analysis all indicated sedimentary environment of clastic rocks of Moshan Formation is fan delta front subaqueous distributary channels. Results of detrital composition, heavy mineral assemblages and U-Pb isotope chronologic dating suggest that the provenance of clastic rocks are mostly derived from South China Plate, and Susong complex in Dabie orogenic belt also provide a small amount of detritus. The lack of garnets and Triassic metamorphic zircons suggest that the high pressure-ultrahigh pressure metamorphic rocks may have not been exposed to the surface in the Early Jurassic.