北喜马拉雅E-W向伸展变形时限:来自藏南错那洞穹隆Ar-Ar年代学证据

特提斯喜马拉雅带以广泛发育近E-W向和近S-N向断裂以及北喜马拉雅片麻岩穹隆带为典型特征.藏南错那洞穹隆位于特提斯喜马拉带的东部，是近两年新发现并厘定的穹隆构造.该穹隆从外向内主要由3部分组成:上部单元（盖层）、中部单元（滑脱系）和下部单元（核部），其中滑脱系主要由一套强烈变形的片岩、伟晶岩、花岗岩、大理岩和矽卡岩组成，片岩包括含石榴石云母片岩、含石榴石十字石云母片岩、含蓝晶石石榴石十字石片岩、含矽线石蓝晶石石榴石片岩和云母石英片岩.野外构造变形特征表明滑脱系为一条强烈变形的韧性剪切带，发育大量的鞘褶皱、"Z"形揉褶皱和眼球状构造、石榴石的旋转碎斑、S-C组构和压力影构造.错那洞穹隆记录了4期构造变形:第1期由北向南的逆冲挤压构造、第2期由南向北的韧性伸展构造、第3期近E-W向的韧性伸展构造变形和第4期成穹后的脆性垮塌构造.通过对滑脱系中含石榴石云母片岩的白云母进行Ar-Ar同位素测年，获得坪年龄为14.0±0.2 Ma，等时线年龄为13.7±0.5 Ma，二者基本一致，同时微观构造特征显示石英呈亚颗粒旋转重结晶（SGR），其韧性变形的温度为450~550℃，该变形温度高于白云母的封闭温度.因此，白云母Ar-Ar坪年龄（14.0±0.2 Ma）代表错那洞穹隆近E-W向伸展变形的时间，也即近S-N向桑日-错那裂谷的活动时间.结合构造变形和年代学特征，认为错那洞穹隆是STDS向北伸展拆离的主导机制叠加后期近E-W向韧性伸展活动的结果. 

Timing of E-W Extension Deformation in North Himalaya: Evidences from Ar-Ar Age in the Cuonadong Dome,South Tibet

The Tethys Himalaya is characterized by the S-N trending and E-W trending structures, and the North Himalaya gneiss domes (NHGD).The Cuonadong dome, located at the eastern part of the North Himalaya, is a recently newly identified dome.The Cuonadong dome is divided into three units from outer to inner:the upper unit (the cover rocks), middle unit (the detachment layer) and lower unit (the core).The middle unit mainly consists of a series of strong deformation schist, pegmatite, granite, marble, and skarn.The main schist types include garnet mica schist, garnet staurolite schist, kyanite garnet staurolite schist, sillimanite kyanite garnet schist, and mica quartz schist.This unit is characterized by a ductile shear zone including the sheath fold, augen structure, rotating porphyroclast, S-C structure, and pressure shadow structure.The Cuonadong dome preserves evidences for four major deformational events:N-S thrust (D₁), early approximately S-N extensional deformation (D₂), approximately E-W extensional deformation (D₃), and collapse structural deformation (D₄).Ar-Ar dating of muscovite from the mylonitic schist in the Cuonadong dome yielded Ar-Ar plateau age of 14.0±0.2 Ma and inverse isochron age of 13.7±0.5 Ma, meanwhile the presence of subgrain rotation recrystallization (SGR) in quartz shows that the schist was deformed under high deformation temperature (450~550℃), which is clearly higher than the closure temperature of muscovite.Therefore, we suggest that the Ar-Ar plateau age of 14.0±0.2 Ma represents the age of the E-W extensional deformation in the Cuonadong dome, also the age of the S-N trending Sangri-Cuona rift.Combined with the structural deformation and thermochronology, we suggest that the formation of the Cuonadong dome resulted from both the earlier S-N and later E-W extensional deformations, especially the S-N extensional deformation, i.e.the STDS.