Structures,kinematics,thermochronology and tectonic evolution of the Ramba gneiss dome in the northern Himalaya  

作　　者：Lei Guo Jinjiang Zhang Bo Zhang 

机构地区：[1]The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, China School of Earth and Space Sciences, Peking University, Beijing 100871, China

出　　处：《Progress in Natural Science:Materials International》2008年第7期851-860,共10页自然科学进展·国际材料（英文版）

基　　金：supported by National Natural Science Foundation of China(Grant No.40572115).

摘　　要：The Ramba gneiss dome, one of the north Himalayan gneiss domes, is composed of three tectono-lithologic units separated by an upper and a lower detachment fault. Low-grade metamorphic Tethyan Himalayan sedimentary sequence formed the upper unit above the brittle upper detachment fault. Mylonitic gneiss and a leucogranite pluton made up the lower unit beneath the ductile lower detachment fault. Mylonitic middle-grade garnet-, staurolite- and andalusite-schist constituted the middle unit between the two faults, which may be that the basal part of the upper unit experienced detachment shear. The Ramba dome underwent three episodes of deformation in its tectonic evolution. The first episode was a top-down-to-north-northwest sliding possibly related to the activity of the south Tibetan detachment system （STDS）. The second episode was the dominant deformation related to a east west extension, which resulted in a unique top-down-to-east kinematics and the major tectonic features of the dome. The third episode was a collapse sliding toward the outsides of the dome. The Ramba gneiss dome is possibly a result of the east-west extension and magmatic diapir. The lower detachment fault is probably the main detachment fault separating the sedimentary sequence from the crystalline basement during the eas-west extension in the dominant deformation episode. The diapir of the leucogranite pluton formed the doming shape of the Ramba gneiss dome. This pluton intruded in the core of the dome in a late stage of the dominant deformation, and its Ar-Ar cooling ages are about 6 Myr. This indicates that the dominant deformation of the dome happened at the same time of the east west extension represented by the nort-south trending rifts throughout the northern Himalaya and southern Tibet. Therefore, the formation of the Ramba gneiss dome should be related to this east west extension.The Ramba gneiss dome,one of the north Himalayan gneiss domes,is composed of three tectono-lithologic units separated by an upper and a lower detachment fault.Low-grade metamorphic Tethyan Himalayan sedimentary sequence formed the upper unit above the brittle upper detachment fault.Mylonitic gneiss and a leucogranite pluton made up the lower unit beneath the ductile lower detach- ment fault.Mylonitic middle-grade garnet-,staurolite-and andalusite-schist constituted the middle unit between the two faults,which may be that the basal part of the upper unit experienced detachment shear.The Ramba dome underwent three episodes of deformation in its tectonic evolution.The first episode was a top-down-to-north-northwest sliding possibly related to the activity of the south Tibetan detachment system(STDS).The second episode was the dominant deformation related to a east–west extension,which resulted in a unique top-down-to-east kinematics and the major tectonic features of the dome.The third episode was a collapse sliding toward the outsides of the dome.The Ramba gneiss dome is possibly a result of the east–west extension and magmatic diapir.The lower detachment fault is probably the main detachment fault separating the sedimentary sequence from the crystalline basement during the east–west extension in the dominant deformation episode.The diapir of the leucogranite pluton formed the doming shape of the Ramba gneiss dome.This pluton intruded in the core of the dome in a late stage of the dominant deformation,and its Ar–Ar cooling ages are about 6 Myr.This indicates that the dominant deformation of the dome happened at the same time of the east–west extension represented by the north–south trending rifts throughout the northern Himalaya and southern Tibet.Therefore,the formation of the Ramba gneiss dome should be related to this east–west extension.

关 键 词：Ramba gneiss dome North Himalayan gneiss domes East west extension 

分 类 号：P54[天文地球—构造地质学]