江南造山带内二叠系硅质岩的地球化学特征及其地质意义

Geochemical Characteristics of the Permian Chert in the Jiangnan Orogenic Belt and its Geological Implications

本文采用常量、微量和稀土元素岩石地球化学方法对华南地区江南造山带内二叠系硅质岩的成因及形成的大地构造背景进行了详细研究。结果表明,江南造山带内的二叠系硅质岩均为含陆源泥质较高的泥硅岩,热水成因与正常沉积成因并存,且形成于大陆边缘、大洋盆地、洋脊等不同构造部位,指示这一时期的强烈构造拉张,在拉张强烈的部位形成了小洋盆和洋壳。此外由稀土配分模式的差异性表明二叠纪江南造山带的构造活动表现为幕式的拉张,并伴随多期热液活动,且不同构造时期形成的硅质岩表现出截然不同的地球化学特征。

The origin of Permian cherts and geotectonic formation background of the Jiangnan orogenic belt in the South China has been studied on the basis of the geochemistry of its major elements, trace elements and rare-earth element （REE）. Results show that Permian cherts, which formed at different tectonic positions, such as continen- tal margin, ocean basin and oceanic ridges, are all muddy cherts. The Permian cherts contain high contents of ter- rigenous muds and originate from both hydrothermal and sedimentary sources. These indicate that an intense tec- tonic extension existed in this period and that small ocean basin and ocean crust were formed in high extension spots. The different REE distribution modes indicate that tectonic in the belt is episodic stretch that accompanied by multi-stage hydrotherma[ activity, and that cherts formed at different period exhibit entirely different geochemical characteristics.