桂西巴马地区极高Ti/Y值基性岩地球化学特征——来自峨眉山地幔柱高Ti母岩浆?  

Geochemistry of extreme high Ti/Y mafic rocks from western Guangxi: Implications for the primitive magma of high Ti basalt of Emeishan mantle plume?

作　　者：黄文龙[1] 刘希军[1] 时毓[1] 许继峰[1,2] 廖帅[1] 郭琳[1] 吴伟男[1] 李政林[1] 梁琼丹[1] 

机构地区：[1]广西隐伏金属矿产勘查重点实验室/桂林理工大学地球科学学院,广西桂林541004 [2]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,广东广州510640

出　　处：《地质通报》2015年第2期474-486,共13页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:41463002;41302041);广西自然科学基金项目(编号:2014GXNSFBA118218;2012GXNSFCA053007);广西八桂学者项目(2013);广西隐伏金属矿产勘查重点实验室系统性研究课题(编号:13-A-01-01);桂林理工大学博士启动基金

摘　　要：桂西地区位于扬子地块西南缘,越北地块以北。桂西巴马等地出露层状—似层状基性岩(辉绿岩和玄武岩),该地区的基性岩成因对于理解该区构造—岩浆作用具有十分重要的意义。对桂西巴马基性岩进行了岩石学和地球化学研究,对其岩石成因和岩浆源区特征进行了讨论。研究表明,桂西巴马基性岩属于碱性玄武质岩,相对富集轻稀土元素和Nb、Ti等微量元素,与峨眉山大火成岩省高Ti玄武岩相似,说明其与峨眉山地幔柱具有相关性。然而,对比峨眉山高Ti玄武岩,巴马基性岩表现出更高的Ti/Y值。不相容元素比值特征表明,桂西巴马基性岩岩浆演化呈现更高的Nb/Y值等演化趋势。结合Dy/Dy*与Dy/Yb、Ti/Y的协变关系,对桂西基性岩与峨眉山玄武岩岩浆源区中稀土元素的分异特征进行判别,揭示出桂西巴马基性岩和峨眉山高Ti玄武岩具有同源性。然而,巴马基性岩地幔熔融程度更低,可能是峨眉山大火成岩省外带的地幔柱岩浆作用延伸的结果,代表了峨眉山地幔柱高Ti玄武岩母岩浆的特征。Bama area in western Guangxi is located on the southwestern margin of the South China Block and the northern side of North Vietnam Block. Late Permian mafic rocks are well cropped out around Bama County. Deciphering the petrogenesis of Bama mafic rocks is crucial to the understanding of the tectonic-magmatic evolution of western Guangxi. This paper presents geochemical data（major and trace elements data）of Bama mafic rocks and discusses the petrogenesis and mantle sources of Bama mafic rocks. Studies indicate that the Bama mafic rocks mainly belong to alkaline basalt. These rocks are relatively enriched in LREE and Nb, Ti,and have similar trace element characteristics to the high Ti basalts from the Emeishan mantle plume, suggesting that they shared a common mantle source. However, the Bama mafic rocks show relatively higher Ti/Y ratios than the Emeishan high Ti basalts. The incompatible trace elements ratios covariance diagram that can trace the mantle source reveals that the Bama mafic rocks have an ex-tremely high Nb/Y evolution trend. According to Dy/Dy？ versus Dy/Yb and Ti/Y covariance diagrams, the authors hold that the Bama high Ti/Y mafic rocks experienced a lower degree mantle partial melting than the Emeishan high Ti basalts, although they like-ly shared the same mantle plume source. Thus, the Bama mafic rocks are magmatic products in the outer zone of the Emeishan Large Igneous Province and probably represent the primitive magmas of Emeishan high Ti basalts.

关 键 词：桂西巴马 高Ti/Y值基性岩 峨眉山地幔柱 地球化学 

分 类 号：P588.124[天文地球—岩石学]