藏南冈底斯岩基晚白垩世构造岩浆作用:以拉萨白堆复合岩体中-基性岩脉群为例

发布时间：2019-01-05 14:19

【摘要】：拉萨白堆复合岩体寄主为含包体的花岗闪长岩,并被一系列平行-近平行东西走向中-基性岩脉群穿插,总体形成类似"条纹码"般的构造形式。锆石U-Pb定年表明,这些基性岩脉主要形成于85~68Ma。同期中性和基性脉岩都表现出富集大离子亲石元素和LREE,亏损高场强元素,Sr同位素初始比值较低,但Nd同位素比值(εNd(t)+3.1)和锆石Hf同位素组成(εHf(t)+10.7)较高,都不具有Eu异常。与中性脉岩相比,基性脉岩具有(1)Mg O含量较高和较高的Mg#(50.6);(2)较高的Cr、Ni、Co含量;(3)较富集HREE且平坦分布。但中性脉岩Y含量较低,Sr/Y比值(38~72)较高,具有高Sr-低Y的特征;这些特征表明:这些岩浆岩的源区可能为受流体交代的岩石圈地幔。中-基性脉岩之间具有岩浆演化关系,在岩浆演化过程中以角闪石的分离结晶为主。结合文献数据,这些新数据表明冈底斯岩基的在晚白垩世(85~68Ma)经历了弧上伸展构造作用,岩浆作用持续活动,可能与新特提斯洋板片的北向斜俯冲相关。
[Abstract]:The Baidui complex in Lhasa is hosted by granodiorite containing inclusions and is interlaced by a series of parallel-near parallel east-west-middle-basic vein groups, forming a structural form similar to "stripe code". The zircon U-Pb dating indicates that these basic veins were mainly formed at 8580 Ma. During the same period, both neutral and basic dikes show enrichment of large ion lithophile elements and LREE, depletion of high field strength elements, and the initial ratio of Sr isotopes is relatively low. However, Nd isotope ratio (蔚 Nd (t) 3.1) and zircon Hf isotopic composition (蔚 Hf (t) 10.7) are relatively high, and there is no Eu anomaly. Compared with the neutral dike rocks, the basic dikes have higher (1) Mg O) and higher Mg# (50.6); (2) higher Cr,Ni,Co contents, (3) higher HREE enrichment and flat distribution. But the Y content of neutral dike rock is lower and the Sr/Y ratio (38 ~ 72) is higher, which indicates that the source area of these magmatic rocks may be fluid metasomatic lithospheric mantle. There is a magmatic evolution relationship between the meso-basic dikes and the separation and crystallization of amphibole during the magmatic evolution. These new data indicate that the late Cretaceous (85~68Ma) rock base experienced arc extensional tectonism and continued magmatism, which may be related to the north syncline subduction of the NeoTethys ocean plate.
【作者单位】：中国地质科学院地质研究所;中国地质科学院矿产资源研究所;中国科学院地质与地球物理研究所岩石圈演化国家重点实验室;
【基金】：国家重点研发计划(2016YFC0600304) 公益性行业科研专项(201511022) 国家自然科学基金项目(41425010) 中国地质调查局地质调查项目(12120115027101)联合资助
【分类号】：P534.53;P588.1

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