右江盆地基性岩的地球化学演化特征及其区域构造意义  

Geochemical evolution characteristics and regional tectonic significance of mafic rocks from Youjiang Basin

作　　者：李政林[1,2] 刘希军[1,2,3,4] 许继峰[1,2,5] 康志强[1,2] 时毓[1,2] 黄文龙[1,2] 陈雪峰[1,2] 吴伟男[1,2] 梁琼丹[1,2] 姚野[1,2] 

机构地区：[1]桂林理工大学广西隐伏金属矿产勘查重点实验室,广西桂林541004 [2]桂林理工大学地球科学学院,广西桂林541004 [3]南京大学内生金属矿床成矿机制研究国家重点实验室,南京210093 [4]南京大学地球科学与工程学院,南京210093 [5]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广州510640

出　　处：《桂林理工大学学报》2015年第4期727-735,共9页Journal of Guilin University of Technology

基　　金：国家自然科学基金项目(41463002;41302041);广西自然科学基金项目(2014GXNSFBA118218;2014GXNSFBA118220);广西科学研究与技术开发计划项目(桂科能1598025-14);同位素地球化学国家重点实验室(中国科学院广州地球化学研究所)开放基金项目(SKLIG-KF-14-04);广西"八桂学者"创新团队项目(2013;有色金属成矿理论与勘查技术)

摘　　要：右江盆地二叠—三叠纪高、低Ti基性岩具有明显的空间分布规律,高Ti基性岩（Ti/Y〉500）集中在盆地中部、西南部,而低Ti基性岩（Ti/Y〈500）集中在富宁-那坡-靖西-凭祥地区,呈北西向且沿着印支期断裂构造分布。高Ti基性岩属于碱性辉绿岩或玄武岩,轻稀土（LREE）相对富集,重稀土（HREE）相对亏损,（La/Yb）_N=6.49~8.83,曲线整体与OIB一致;低Ti基性岩为亚碱性的辉绿岩或玄武岩,并具有向安山岩过渡的趋势,其轻、重稀土分异不明显,（La/Yb）_N=1.1~4.3,Nb、Ta强烈亏损。微量元素判别图解表明：右江盆地高Ti基性岩是与峨眉山地幔柱相关的板内玄武岩,而低Ti基性岩是E-MORB或NMORB部分熔融的产物。高、低Ti基性岩空间与时间的高度重合,以及桂西南与越南北部地区中、酸性岩体的俯冲造山及峨眉山地幔柱成因,暗示低Ti基性岩可能是由峨眉山地幔柱造成的上涌软流圈岩浆与地壳混染的产物,并与印支期的板块运动有关。Permian- Trassic mafic rocks,well cropped out in Youjiang Basin,have a clear spatial distribution of high-Ti and low-Ti mafic rocks. The high-Ti mafic rock mainly distributes in the central and southwest of Youjiang Basin,while the low-Ti mafic rock almost distributes at Funing-Napo-Jingxi-Pinxiang area,NW trending and controlled by the Indosinian fracture structure. The geochemical results indicate that the high-Ti mafic rock is alkaline basalts,enriched in LREE and depleted in HREE with（ La / Yb）N= 6. 49- 8. 83,similar with OIB. However the low-Ti mafic rock has a wider transitional signatures ranging from subalkaline basalt to andesite,displays a weak fractionation between LREE and HREE with（ La / Yb）N= 1. 1- 4. 3,but a strong depletion of Nb and Ta. Trace elements ratios suggest that the high-Ti mafic rock is likely derived from the Emeishan mantle plume,but the low-Ti mafic rock experienced partial melting of E-MORB-and N-MORB-like magma.The spatial overlap of low-Ti and high-Ti mafic rocks,as well as the medium-acid rocks,formed by subduction orogenic and Emeishan mantle plume in Southwest Guangxi and North Vietnam,suggest that the low-Ti mafic rock is likely formed by a mixed compound in Emeishan mantle plume or asthenosphere and continental crust,and this process may be associated with the plate motion of Indo-Chinese epoch.

关 键 词：基性岩 二叠—三叠纪 地球化学特征 右江盆地 

分 类 号：P588.124[天文地球—岩石学]