CAJ | 학술논문

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。
대서곤륜조산대동단아강화산암진행료암석학화지구화학연구,결과현시하단현무암속우저갑랍반계렬, N b-Ta불우손,구유교고적Nb/La비치(0.49~1.46,평균=0.98), LREE부집적우경희토원소배분모식, HREE내부분이교약,불상용원소조성상사우대양고원현무암,현시원구제연류권성분외,환유 EMII 조분적가입；상단현무–안산암조합위구유유사도호현무암지구화학특정적랍반계렬암석,부집LREE、LILE,우손Nb-Ta、Ti등,래원우조기판괴부충작용개조적대륙암석권지만,주요결정분이상위감람석+단사휘석+사장석。서곤륜동단이첩기랍반질현무암연구표명,구역상정체처우륙연렬곡혹호후분지대지구조배경,지만원구구유다양성。
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.