摘要
北祁连加里东朝俯冲－增生楔可分为浅部和深部两个单元。浅部单元主要由蛇绿岩、蛇绿混杂岩及深海复理石所组成，极浅变质或没有变质。深部单元主要由ＨＰ／ＬＴ蓝片岩、透镜状的蛇纹岩、变辉长岩及绿片岩（主要为退变质产物）所组成。普遍遭受ＨＰ／ＬＴ变质作用和绿片岩相的退变质作用。两个单元同时形成于不同的构造层次，具有类似的原岩特征。在加里东期，俯冲－增生楔共经历４期变形作用（Ｄ１，Ｄ２，Ｄ３，Ｄ４）和３期变质作用（Ｍ１，Ｍ２，Ｍ３）。从Ｄ１→Ｄ４反映了俯冲－增生楔从俯冲作用→深部构造板底垫托作用→折返（构造顶蚀）→剥蚀的动力学演化过程。
The North Qilian Caledonnian subduction accretionary wedge may be subdivided into deep and shallow unit.The shallow unit,which mainly consists of ophiolite,ophiolitic melange and marine flysch distributed in the front part of wedge undera very low metamorphic conditon,was formed by off scrapping of marine sediments and mafic ocean crust.On the other hand,the deep unit,which mainly composed of HP/LT Blueschists,lenticuler serpentinites,meta gabbros and greenschist rocks developed in the deep part of the subduction zone,is associated with tectonic underplating.The two units are coeval and produced at different levels with similar protoliths.During Caledonian period(460-410Ma) the subduction accretionary wedge experienced four stage deformation(D 1,D 2,D 3,D 4) and three stage metamorphism (M 1,M 2,M 3).D 1 and D 2 are characterized by formation of thrust shear zone with a top to the north(of NNE) sense of shear under HP/LT condition (M 1,M 2) and are associated with tectonic underplating in the subduction zone as a result of Qilian ocean subducting under Alashan Block.D 3 resuled in extension ductile shear zone concetrated on greenschist rocks (M 3,formed buy retro metamoorphism of HP/LT rocks) and indicated a top to the south normal sense of shear.During D 3 early ductile thrust shear zone was reactivated as a normal shear zone.Moreover,D 3 is linked to preservation of HP/LT rocks.In the region with less D 3 deformation,HP/LT mineral assemblges are well preserved,whereas in the extension ductile shear zone indicating strong D 3 deformation,D1+2 deformation structure and HP/LT assmblages are only found locally as relicts,S 1 and S 2 are transposed by penetrative S 3,and HP/LT minerals are almost replaced by greenschist face mineral assemblges.However,the extension ductile shear zone related to D 3 led to exhumation(tectonic unroofing) of HP/LT rocks of its basewall.D 4 is defined by gentale folds without crenulation cleavages and may represent a higher level deformation during late exhumation.D 1→D 4
出处
《地质科学》
CAS
CSCD
北大核心
1998年第3期290-299,共10页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家自然科学基金
关键词
北祁连山
加里东期
俯冲结构
增生楔结构
动力学
North Qilian,Caledonian subduction accretionary wedge,HP/LT blueschist,Tectonic unroofing
