中蒙边界区亚干变质核杂岩的组成与结构

COMPOSITION AND TEXTURE OF THE YAGAN METAMORPHIC CORE COMPLEX BORDERING CHINA AND MONGOLIA

亚干核杂岩的变质核由条带状片麻岩、大理岩 糜棱状片 (麻 )岩、糜棱片麻状花岗岩、石英片岩等单位组成 ,拆离带由糜棱岩带、绿泥石化带、微角砾岩—假熔岩带、拆离断层面、断层泥和断层角砾构成 ,上盘岩系主要有二叠系、侏罗系、白垩系以及白云质大理岩异地块体。这些单位从构造角度可归结为 3层结构并发育 2个拆离带 ,显示了多层构造岩片由多个韧性拆离带经过长期递进伸展抬升叠置的特点 ,可能揭示了一种大陆内部多层伸展构造体系的特征。

The Yagan metamorphic core complex (MCC) is composed of low plate metamorphic crystalline core, detachment fault zone and upper plate. The core can be subdivided into two tectonic slices: the high grade metamorphic slice in the lower and the low grade metamorphic slice in the upper. The former consists of amphibolite facies banded gneisses and marble gneisses, and the later of quartz schists. Between the both occurs a granitic mylonite zone. The major detachment fault zone is composed of mylonitic zone, chloritized zone, breccias pseudotachylite zone, fault surface and cataclasitic zone. The upper plate of the MCC consists of anchimetamorphic Permian, Jurassic and Cretaceous as well as exotic blocks of the Proterozoic dolomitic marbles. In a whole, the MCC can be divided, structurally, into three layers separated by two detachment zones, instead of a simple two plate mode. All these units arrange in outward (ascending) order, keeping the original relationship. Additionally, the deformation is characterized by foliation and lineation, instead of folds. Such a feature of stratum framework in extensional regime means structural nappies of extension and elevation of tectonic slices by several detachment zones and shows a characteristics of poly layer extensional tectonic systems. It provides an example that a large scale extensional system, including more than one detachment zones, consists of several tectonic slices, stacking up regularly, as a series of thrust slabs, which may have some rheological information on continental crust section.