西昆仑东段阿羌火山岩成因及其构造意义  

Petrogenesis and Tectonic Implication of the A'qiang Mafic Lavas in the West Kunlun Orogen, NW China

作　　者：高晓峰[1,2] 校培喜[1,2] 康磊[1,2] 计文化[1,2] 杨再朝[1,2] 

机构地区：[1]中国地质调查局西安地质调查中心造山带地质研究中心,陕西西安710054 [2]中国地质调查局西安地质调查中心,国土资源部岩浆作用成矿与找矿重点实验室,陕西西安710054

出　　处：《大地构造与成矿学》2015年第5期949-958,共10页Geotectonica et Metallogenia

基　　金：陕西省自然科学基金(2013KJXX-68);中国地质调查局项目(12120114020501);国家科技支撑专题(2015BAB05B01-01)联合资助

摘　　要：对西昆仑造山带东段阿羌火山岩进行了岩石学和地球化学研究,结果显示下段玄武岩属于低钾拉斑系列, N b-Ta不亏损,具有较高的Nb/La比值（0.49~1.46,平均=0.98）, LREE富集的右倾稀土元素配分模式, HREE内部分异较弱,不相容元素组成相似于大洋高原玄武岩,显示源区除软流圈成分外,还有 EMII 组分的加入；上段玄武–安山岩组合为具有类似岛弧玄武岩地球化学特征的拉斑系列岩石,富集LREE、LILE,亏损Nb-Ta、Ti等,来源于早期板块俯冲作用改造的大陆岩石圈地幔,主要结晶分异相为橄榄石＋单斜辉石＋斜长石。西昆仑东段二叠纪拉斑质玄武岩研究表明,区域上整体处于陆缘裂谷或弧后盆地大地构造环境,地幔源区具有多样性。Petrologic and geochemical analyses have been carried out in aiming to reveal the petrogenesis of the‘Permian’ sub-alkaline basalt of A’qiang volcanic sequence in West Kunlun orogen. The lower basalts exhibit tholeiitic feature and share similar incompatible trace element geochemistry to those of the oceanic plateau basalts, i.e., insignificant Nb-Ta anomaly, higher Nb/La ratios （0.49？1.46, average=0.98）, LREEs enrichment relative to HREEs and flat HREE pattern. Their geochemical features indicate that the primitive magma was derived from a source of convective asthenosphere with involvement of EMII component. The upper basalt-andesite associations have similar trace element geochemical characteristics to the island arc basalt-andesite series, with enrichments in LREEs and LILEs and depletions in Nb, Ta and Ti. We suggest that the upper lavas were derived from an enriched lithospheric mantle, which had been previously modified by slab-released fluids and/or related sediments. Both types of mafic lavas experienced fractional crystallization of olivine, clinopyroxene and plagioclase. Our new results from the ‘Permian’ tholeiitic basalts indicate multiple mantle sources beneath the eastern part of West Kunlun orogen, suggesting the existence of a continental margin rift or a back-arc basin during the late Paleozoic time.

关 键 词：岩石成因 阿羌火山岩 构造属性 西昆仑造山带 

分 类 号：P595[天文地球—地球化学]