It is significant for igneous rocks to study the regional geological setting and geodynamic mechanism.The magmatic activities were very intense in south Tibet,as a response to the India plate colliding to the Eurasia continent.However,there is limited report on igneous rocks in the Tethys-Himalaya antimony-gold metallogenic belt,which was near the Main Center Thrust (MCT).The Integrated Exploration Area of the Zhaxikang Lead-zinc Deposit is located in the eastern part of this metallogenic belt.Recently,we have found a group of bimodal igneous rocks in the Zhaxikang area.In this study,we carried out zircon U-Pb dating and elemental geochemistry studies for the Segang diabase dikes in this area.The results show that these mafic rocks were emplaced in a large scale extensional setting at the period of Early Cretaceous (138～134 Ma),and are characterized by high TiO2,Nb/Y ratio,enrichment of light rare earth elements (LREEs)and incompatible elements.These diabases also exhibit OIB-like REE and trace element patterns.They were likely generated by the Kerguelen plume and had been contaminated by crustal wall rocks.This study is beneficial to understand the Mesozoic tectonomagmatic process and forming mechanism in south Tibet.%岩浆岩对于间接研究构造背景和大地动力学机制具有重要意义.受印度板块向欧亚大陆碰撞造山作用的影响,藏南地区的岩浆活动极为强烈,但在靠近主中央逆冲断裂带(MCT)的特提斯-喜马拉雅锑金成矿带内,目前报道的岩浆岩出露则相对较少.扎西康铅锌多金属矿整装勘查区正是位于该成矿带东部,在勘查区内发现众多的侵入岩浆岩体或岩脉/墙,具有典型的双峰式岩浆岩特征.对区内的色岗辉绿岩墙群进行了锆石U-Pb年代学及元素地球化学研究,结果表明这些铁镁质岩浆岩形成于早白垩世(138～134 Ma),并显示较高的TiO2含量和Nb/Y比值,极度富集轻稀土元素(LREEs)和不相容元素,与洋岛玄武岩(OIB)的特征非常一致,为较大规模伸展构造背景下的产物.色岗辉绿岩群应为软流圈地幔部分熔融产生的基性岩浆在上升过程中受地层围岩不同程度混染下的产物,大地动力学机制可能与古Kerguelen地幔柱的活动相关.该项研究有助于解读藏南地区中生代的构造-岩浆作用及形成机理.
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