日喀则蛇绿岩中辉长-辉绿岩成因及慢速扩张脊环境  

The formation of gabbro and diabase in the Xigaze ophiolite: Implications for a solw-spreading ridge

作　　者：佘宇伟 朱祥坤[1] 何源 万洪清 SHE Yuwei;ZHU Xiangkun;HE Yuan;WAN Hongqing(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质大学地球科学与资源学院,北京100083

出　　处：《中国地质》2019年第6期1372-1383,共12页Geology in China

基　　金：中国地质调查局项目（121201102000150069）;国家自然科学基金（41603022）共同资助~~

摘　　要：日喀则蛇绿岩位于雅鲁藏布构造带中段,其成因和构造环境仍存在较大争议。日喀则蛇绿岩下部为蛇纹石化地幔橄榄岩,壳幔过渡带缺失超镁铁质堆晶岩。少量辉长岩脉呈块状或韵律结构并侵入到地幔橄榄岩和辉绿岩中。辉绿岩呈席状岩床侵入到地幔橄榄岩之上,且少量辉绿岩脉侵入到下覆的地幔橄榄岩中。通过野外关系和地球化学研究,日喀则辉长岩可能并不是洋壳中岩浆房原位结晶堆积而成,而是深部位置岩浆囊经过不同程度分异演化形成富晶粥岩浆并向上侵入的结果。而席状辉绿岩床则是基性岩浆沿着构造薄弱面顺层侵入的结果。拆离断层可能导致了岩石圈地幔抬升和剥露,进而引起下覆软流圈地幔减压熔融和岩浆上侵。日喀则辉长-辉绿岩形成于慢速扩张脊较小规模的岩浆供应和不连续的岩浆侵入。The Xigaze ophiolite is located in the central segment of the Yarlung Zangbo Suture Zone,and its genesis and tectonic setting remain controversial.The ophiolite has a serpentinized peridotites in the lower part,and the ultramafic cumulates are absent in the mantle-crust transition zone.Small amounts of gabbro dikes with isotropic or rhythmic textures intruded into the mantle peridotites or diabase sills.The diabase sills generally intruded along the interface of the mantle peridotites or intruded into the mantle peridotites as diabase dikes.Based on studies of field relationships and geochemical features,the authors hold that,the Xigaze gabbro dikes,instead of being formed by in-situ crystallization of magma chamber in the oceanic crust,might have resulted from the intrusion of crystals-enriched magmas from magma pockets which were distributed in crust-mantle boundary and evolved in variable degrees into silicate-rich minerals.The diabase sills might have been formed from the intrusion of mafic magmas along the structurally weak boundary.The detachment faults probably resulted in the uplift and exhumation of the upper mantle which triggered the upwelling and partial melting of asthenospheric mantle.The gabbro dikes and diabase sills in the Xigaze ophiolite might have originated from small amounts of supply and discrete intrusion of magmas in a slow-spreading ridge.

关 键 词：辉绿岩 辉长岩 蛇绿岩 日喀则 雅鲁藏布 洋中脊 慢速扩张 地质调查工程 青藏高原 

分 类 号：P584[天文地球—岩石学] P595[天文地球—地质学]