Barium isotope evidence for the role of magmatic fluids in the origin of Himalayan leucogranites  

岩浆热液在喜马拉雅淡色花岗岩形成中的钡同位素证据

作　　者：Fang Huang Ruixia Bai Gengxin Deng Xiaochi Liu Xianhua Li 黄方;白瑞霞;邓庚辛;刘小驰;李献华(CAS Key Laboratory of Crust-Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;CAS Center for Excellence in Comparative Planetology,University of Science and Technology of China,Hefei 230026,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]CAS Key Laboratory of Crust-Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China [2]CAS Center for Excellence in Comparative Planetology,University of Science and Technology of China,Hefei 230026,China [3]State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China

出　　处：《Science Bulletin》2021年第22期2329-2336,M0004,共9页科学通报（英文版）

基　　金：supported by the National Natural Science Foundation of China(41803003).

摘　　要：As an important post-collisional magmatic product in the orogenic belt, the Himalayan leucogranites are the critical host rocks for a number of rare-metal mineralization(such as Li, Be, Cs, Rb, Nb, Ta, and Sn).However, there is still a lack of good understanding on the formation and evolution of the leucogranites.Particularly, the role of the magmatic fluids in transporting and enriching the rare elements is not clear.Here we measure Ba isotope compositions for leucogranites from the Kampa Dome of the Himalayan belt to understand the fluid activity and behavior of fluid-mobile elements during leucogranite formation. Our results show that the δ138/134 Ba of leucogranites range from -1.32‰ to +0.12‰, much lower than the literature values for S-type granites and various sedimentary materials, suggesting that the Ba isotope compositions of the leucogranites does not reflect the sedimentary source signatures. Instead, their low δ138/134 Ba is accompanied by non-charge-and-radius-controlled(CHARAC) twin-element(such as Nb/Ta) behaviors, clearly showing the involvement of magmatic fluids during magma evolution.Experimental studies suggest that the low δ138/134 Ba of the magmatic fluids most likely results from exsolution from a large deep magma reservoir. Such fluids not only modified Ba isotope compositions of the leucogranites, but also transported many fluid-mobile metal elements which may help form the rare metal ore deposits. Therefore, Ba isotope data provide new insights into formation and evolution of magmatic fluids and exploration of the rare-metal mineralization.喜马拉雅淡色花岗岩是造山带晚期岩浆作用的特殊产物,是多种稀有金属元素的寄主岩石.目前对淡色花岗岩的认识有待深入,还不清楚岩浆流体对稀有元素富集的影响.本文测量了来自喜马拉雅造山带康巴穹窿的淡色花岗岩的钡同位素组成.淡色花岗岩的δ138/134Ba范围为-1.32‰~+0.12‰,远低于S型花岗岩和沉积物的δ138/134Ba值.它们的δ138/134Ba值及其和Nb/Ta的关系表明了岩浆演化过程中岩浆流体的参与.实验研究表明,岩浆流体的低δ138/134Ba很可能来自较大的深部岩浆储库出溶.这种流体不仅改变了淡色花岗岩的Ba同位素组成,而且还输送了大量有利于形成稀有金属矿床的流体活动元素.因此, Ba同位素数据为淡色花岗岩形成和演化以及稀有金属矿化过程提供了新的见解.

关 键 词：HIMALAYA LEUCOGRANITE Barium isotopes Fluid interaction Rare-metal mineralization 

分 类 号：P588.121[天文地球—岩石学] P597[天文地球—地质学]