华北克拉通及邻区晚中生代伸展构造及其动力学背景的讨论

摘要

Late Mesozoic extension tectonics was quite significant on eastern Eurasia Continent and it was expressed by extensional domal structure such as the metamorphic core complexes,syntectonic plutons,and ductile detachment fault,even graben and half graben basins.According to our field observations,laboratory work and previous research,from north to south,five extension belts have been separated:Transbaikalia-Okhotsk belt,western part of North China Block,eastern part of North China Block,south margin of North China Block and Qinling-Dabie belt and South China Block.As a largest extension tectonic at the scale of crust in the world,these entire belts have NW-SE extensional direction and this extensional structure make the middle to lower curst rocks exhumed to the surface along the detachment normal fault.Geochronological work on these ductile detachment fault indicated a very narrow period around 130 ～ 126Ma except the eastern part of North China Block,which have a width extensional period relatively.Lithosphere delamination could be considered as the geodynamic of this large scale extension tectonic.This geodynamic model could make us to understand the time,scale,and mechanism on the topic of North China Craton destruction from the view of structure analyses.%欧亚大陆东部晚中生代伸展构造十分显著,表现为大量发育的变质核杂岩、同构造岩浆岩、韧性拆离断层带等伸展成因的穹隆和地堑-半地堑盆地.通过对这些伸展构造进行系统分析、归纳和总结,将欧亚大陆东部晚中生代伸展构造发育区划分为:泛贝加尔-鄂霍次克带、华北西部带、华北东部带、华北南缘及秦岭-大别带和华南内陆带.这些伸展构造记录了大区域上的NW-SE方向伸展,构成了全球最大的陆壳伸展地区.这些伸展构造使地壳深部的岩石沿拆离断层折返至地表,从而使中下地壳结构发生了强烈的改造.除华北东部带给出了一个较为宽泛的伸展时段外,各个研究区所涉及的伸展穹隆及其相关的拆离断层所表现的伸展峰期时间均十分相近:位于130 ～ 126Ma之间.岩石圈根部的拆沉可能是这个巨型伸展构造带形成的动力学机制.这个模型为探讨华北克拉通破坏和减薄的时限、机制、模式及深部动力学背景提供直接的构造证据.