大别山低级变质岩的构造背景

大别山南北两侧的浅变质岩是碰撞造山以前洋壳俯冲造山阶段的重要组成部分。木兰山片岩或张八岭群是俯冲的洋壳;苏家河群、信阳群和佛子岭群是由洋壳俯冲形成的海沟沉积,并因俯冲过程中的前进变形而形成增生楔;杨山煤系和梅山群是石炭纪弧前盆地沉积,并因俯冲过程中的前进变形而被增生楔逆掩。宿松群是扬子大陆被动边缘沉积,不是俯冲造山带的成员。因洋壳俯冲形成的弧和弧后盆地可能已被新生界沉积物掩盖。高压-超高压变质带是碰撞造山后期从深部折返的外来体。高压-超高压变质带正好处于洋壳和增生楔之间,破坏了早期洋壳俯冲造山带的完整性,使得洋壳俯冲造山阶段的特征被破坏,因而不易辨别。俯冲造山阶段应为奥陶纪到泥盆纪,碰撞造山阶段应从二叠纪开始。

Tectonic background of low grade metamorphic rocks of the Dabie Mountain

Low grade metamorphic rocks on both the northern and southern sides of the Dabie Mountains are important members of subduction orogen of oceanic crust prior to collision between Sino-Korean and Yangtze cratons. The Zhangbaling Group/Mulanshan schist is an oceanic crust prior to Ordovician. Sujiahe Group, Xinyang Group and Foziling Group are trench sediments of Ordovician-Devonian, and constitute an accretionary wedge during subduction. Yangshan coal series and Meishan Group belong to Carboniferous fore-arc sediments and were overthrusted by accretionary wedge during collision. Susong Group are passive continental sediments of the Yangtze craton. Backarc basin sediments are postulated to be concealed by Mesozoic-Cenozoic sediments to the north of the Dabie Mountains. High and ultra-high pressure terranes are exotic tectonic slices exhumed from depth, which are located in low grade metamorphic rocks, and disturb the integrity of the earlier subduction orogen. Subduction happened during Ordovician to Devonian, and collision initiated at the beginning of the Permian.