北部湾玄武岩地幔源区性质的地球化学示踪及其构造环境  

GEOCHEMICAL NATURE OF MANTLE RESERVOIRS AND TECTONIC SETTING OF BASALTS IN BEIBU GULF AND ITS ADJACENT REGION

作　　者：贾大成[1] 丘学林[2] 胡瑞忠[3] 卢焱[1] 

机构地区：[1]吉林大学地球探测科学与技术学院,吉林长春130026 [2]中国科学院南海海洋研究所,广东广州510301 [3]中国科学院地球化学研究所矿床地球化学开放研究实验室,贵州贵阳550002

出　　处：《热带海洋学报》2003年第2期30-39,共10页Journal of Tropical Oceanography

基　　金：中国科学院知识创新工程项目 (KZCX2- 2 0 9);(KZCX2 10 2 );中国科学院南海海洋研究所边缘海地质与古环境开放实验室基金项目 (BYH0 1A0 2 );中国科学院地球化学研究所矿床地球化学开放研究实验室基金项目(2 0 0 0 )资助

摘　　要：北部湾发育一系列上新世玄武岩 ,其全岩K Ar年龄为 5 .9— 2 .4Ma ,是伴随北部湾盆地拉张而形成的一次较大规模的岩浆活动。岩石化学和微量元素地球化学研究表明 ,该玄武岩属于碱性玄武岩系 ,具有OIB型微量元素配分模式 ,形成于较均一的地幔源区 ,具有以EM2型地幔端元为主、混有HIMU和EM1型端元的地幔源区性质 ,形成于地幔柱或地幔热点的构造环境。北部湾盆地与红河剪切断裂带具有相同的地幔源区 ,而与受太平洋板块影响的地幔源区差别较大。玄武岩形成和北部湾盆地拉张主要受印度板块向欧亚板块俯冲导致的红河断裂带大规模剪切走滑控制 ,5Ma左右红河断裂带由左行走滑剪切转变为右行走滑剪切的构造性质转换可能是导致地幔异常扰动和岩浆活动的地球动力学机制。A series of basalts developes in the Beibu Gulf region. The K-Ar ages of the basalts ranges from 5.9Ma to 2.4Ma. They were formed by a large-scale magmatic activity associated with extension of the basin in the Beibu Gulf. Geochemical studies of major elements and trace elements indicated that the basalts belong to an alkali series and are similar to OIB. The basalts may be derived from a uniform mantle source. The mantle source has the nature of EM2 end-member composition associated with HIMU and EM1 end-member. The basalts might be formed in a plume or mantle hot spot. Formation of the basalts and extension of the basin in the Beibu Gulf were controlled by the large-scale strike-slip of the Red-River fault zone, which was caused by subduction between Indo-Australia plate and Eurasia plate. Tectonic conversion from left lateral shear to right lateral shear of the Red-River fault zone at about 5 Ma may be attributed to the geodynamic mechanism of mantle abnormal change and magmatic activity.

关 键 词：玄武岩 K—Ar年龄 岩浆活动 岩石化学 微量元素地球化学 地幔源区性质 红河断裂带 地球动力学机制 

分 类 号：P588.145[天文地球—岩石学]