马超营断裂带及其北侧熊耳群火山岩的变质作用

Metamorphism of xiong' er group volcanic rocks in Machaoyin fault zone and its northern side

本文论述了熊耳山南坡的马超营断裂带及其北侧熊耳群火山岩的区域变质作用、动力变质作用和热液变质作用的特点。火山岩的变质作用及其强度在空间分布上表现出不均匀性 ,一般在断裂带内发育且强度大 ,断裂带北侧变质程度低、强度小 ;马超营断裂带对区内熊耳群火山岩的变质作用特征起着一定程度的控制作用 ;变质作用具有多次叠加、改造的特征 ,一般区域变质作用较早较普遍 ,动力变质和热液变质作用偏晚和较局限 。

This paper deals with the charcteristics of the regional metamorphism,dynamicmetamorphism and hydrothermal metamorphism of Xiong'er group volcanic rocks in Machaoyin fault zone and its northern side.The metamorphism of the volcanic rocks presents heterogeneous in spatial distribution and it intensifies,along the fault zone. Because of the protection of craton basement and the stress unloading by faulting,the metamorphism degree of the volcanic rocks in the north side of the fault zone is low,and the intensity is decreased. The Machaoyin fault zone in certain degree controls the metamorphism characteristics of Xiong'er group volcanic rocks. The regional metamorphism of Xiong'er group volcanic rocks is not very imtensive,only reachs the green schist facies; it is more intensive in the fault zone,in places where the temperature and pressure higher, can reach low hornblendite facie. The metamorphism temperature is 400～500℃, pressure is 2.5～4.8Kb,corresponding to depth 6.5～13.5km. The metamorphism age is possibly of Xiaoxiongian Period(1350Ma)-Lulinian Period(1050Ma). The dynamic metamorphism often distributes beltlike,and has close relation to the fold and fault. In the southern side of Machaoyin fault zone along the close Chongdv-Shanmen overturned anticline ,the volcanic rocks subjected to dynamometanorphysm strongly; in its northern side along the wide open Hangou-Lizhipin syncline,the dynamic metamorphism of the volcanic rocks is weak. Whithin the fault zone the dynamic metamorphism is most intensive and the deformation of the rocks is very complex. The dynammetamorphic rocks such as tectonic schists,mylonites,cataclasites,tectonic breccias and tectonic hybrid rocks are mainly affected by the fold and fault in space,distribute along major faults formed by the later stage tectogenesis,and overlapped to the regional metamorphism.The dynamometamorphism generally weakens from south to north and at the same time,has asymmetrical zoning centred with Machaoyin fault zone.Belonging to the ductile-brittle deformation,of the middle-low levels,the dynamic metamorphism was caused by the pressure and temperature conditions. The chemical composition of the schists hardly changes. The hydrothermal metamorphism of the volcanic rocks is mainly controlled by fault, forming late metasomatites,such as veinlet and impregnation,which distributes along the tectonic fractures with zoning,in places associates mineralization. It mainly includes silicification, K-feldsparization, sericitization, (pyrite-)phyllitization, carbonatization and chloritization etc.In course of the hydrothermal metamorphism,the chemical composition of the rocks all changes in different degrees.