%0 Journal Article
%T Characteristics and significance of CH4-rich fluid inclusions from the mafic-ultramafic complex at the Xiangshan, eastern Tianshan Mountains, Xinjiang of China<br>东天山香山镁铁-超镁铁岩中富CH4流体包裹体的特征及其意义
%A PAN XiaoFei
%A LIU Wei State Key Laboratory of Lithosphere Tectonic Evolution
%A Institute of Geology
%A Geophysics
%A Chinese Academy of Sciences
%A Beijing
%A China
%A <br>潘小菲
%A 刘伟
%J 岩石学报
%D 2005
%I 
%X Post-collisional Cu-Ni-bearing mafic-ultramafic intrusive complexes densely occur in the eastern Tianshan Mountains, Xinjiang of China. Compositions of rock and, especially, fluid in their source region remain to be resolved. Xiangshan pluton is typical of the mafic-ultramafic complexes in the eastern Tianshan Mts. It comprises pendotite, gabbro-norite, diorite and gabbro-diabase. Megacrysts of poikilitic hornblende that is abundant in all the rock phases have grown around olivine and labrador, indicating that the parent magma is rich in water. Studied samples were collected from the fresh gabbro-norite in the central body of the Xiangshan pluton. Labrador- and olivine-hosted fluid inclusions occur in isolation or in group without obvious orientation. Fluid inclusion trails were observed occurring parallel to the grain boundary or growth plane of the host mineral. Fluid inclusions are primary or secondary and were trapped during growth of the host mineral or extensive exsolution of fluid from the magma as marked by the crystallization of hornblende. Hence, these fluid inclusions represent fluids derived from the source region. Available stable sulfur and lead isotopic data show meteoric affinity and normal common lead characteristics, respectively. Therefore, crustal contribution for rock and fluid via assimilation or infiltration can be excluded. Bubbles of more than 50 fluid inclusions were analyzed using micro-laser Raman spectrometer. It is shown by the analysis that CH4 and H2O are the dominant gas species, and hydrocarbons C2H2 , C2H6, and C4H6, and N2 are the subordinate gas species in the vapor phase of these fluid inclusions. Four types of vapor compositions are distinguished that include a) CH4-rich vapor,b) H2O-rich vapor, c) H2O + CH4 mixing vapor, and d) multi-species (C2H6 + N2 + CH4 , C2H6 + CH4 + N2 +C4H6) mixing vapor. Therefore, fluids that are brought by the Xiangshan pluton from the mantle source region are rich in H2O and reductive volatiles CH4 etc. Because CO2 fluid instead of CH4 fluid is abundant in the upper mantle whose redox state is near to fayalite-magnetite-quartz buffer, it is likely that the parent magma and inclusion fluids of the Xiangshan pluton derive from the transition zone of the mantle or asthenosphere underneath the Paleozoic orogens of the northern Xinjiang. Subducted slab brought water to the un-oxidized deep mantle during the subduction period before the end of the Early Carboniferous. Mixing of water with the reducing CH4-rich C-H fluids played an important role in the melting of the deep mantle, thereby resulting in the production of widespread post-collisional mafic-ultramafic complexes and the related Cu-Ni sulfide ore deposits.
%K Laser Raman spectroscopy
%K CH4-rich fluid inclusion
%K Mantle transition zone
%K Post-collisional mafic-ultramafic complex
%K Eastern Tianshan Mountains<br>激光拉曼光谱
%K 富CH4流体包裹体
%K 地幔过渡带
%K 碰撞后镁铁-超镁铁杂岩
%K 东天山
%U http://www.alljournals.cn/get_abstract_url.aspx?pcid=E62459D214FD64A3C8082E4ED1ABABED5711027BBBDDD35B&cid=621CF755B1A341E5&jid=2013B5467E3054B1614CEC199353FCED&aid=7303DDFB2FF27FE2&yid=2DD7160C83D0ACED&vid=659D3B06EBF534A7&iid=CA4FD0336C81A37A&sid=CC0ECB9C52F1B85F&eid=AD16A18DBD734D13&journal_id=1000-0569&journal_name=岩石学报&referenced_num=1&reference_num=25