Origin of Li-F-rich granite: Evidence from high P-T experiments  

作　　者：LI Fuchun ZHU Jinchu RAO Bing JIN Zhangdong ZHANG Linsong 

机构地区：[1]School of Resource and Environment Sciences,Nanjing Agriculture University,Nanjing 210095,China [2]State Key Laboratory for Mineral Deposits Research,Nanjing University,Nanjing 210093,China [3]Nanjing Institute of Geography and Limnology,Chinese Academy of Sciences,Nanjing 210008,China

出　　处：《Science China Earth Sciences》2004年第7期639-650,共12页中国科学（地球科学英文版）

基　　金：This work was supported by the National Natural Science Foundation of China (Grant Nos. 40073008 and 40132010) ; the China Universities PhD Subject Foundation Project (Grant No.1999028420).

摘　　要：Though magmatic origin of Li-F-rich granite has been supported effectively by the existence of volcanic and subvolcanic rocks and melt inclusions trapped in them with similar chemical compositions, evidence from high T-P experiments is poor up to now. To simulate the evolution process of Li-F-rich granite and to interpret its forming mechanism, a series of melting-crystallization experiments were carried out. Under the conditions of 1×108 Pa and 570–700°C, a magmatic mineral association of quartz + alkali feldspar + lithium muscovite/ferromuscovite ± fluorite ± cassiterite is found in leucogranite-HF-H2O system. This indicates the following points: (i) Fluorite, light-colored muscovite and cassiterite can crystallize directly from the Li-F-rich granitic melt. (ii) The coexistence of dark-colored micas (e.g. biotite) and light-colored micas (e.g. lithium muscovite and ferromuscovite) suggests that the muscovite granite and two-mica granite can be formed under magmatic condition. The zonal texture of micas is not the sole feature for the micas of hydrothermal origin. (iii) As crystallization proceeds, the SiO2 concentration of the residual melt decreases, while the Al2O3 and F concentrations and A/CNK, NKA/Si ratios of the melt incerese, favoring the formation of Li-F-rich granites. Our experiment results are well consistent with the vertical zonation widely observed in rare metal bearing granites, and therefore provide strong experimental evidence for magmatic origin of Li-F-rich granite.Though magmatic origin of Li-F-rich granite has been supported effectively by the existence of volcanic and subvolcanic rocks and melt inclusions trapped in them with similar chemical compositions, evidence from high T-P experiments is poor up to now. To simulate the evolution process of Li-F-rich granite and to interpret its forming mechanism, a series of melting- crystallization experiments were carried out. Under the conditions of 1108 Pa and 570—700℃, a magmatic mineral association of quartz + alkali feldspar + lithium muscovite/ferromuscovite ?fluorite cassiterite is found in leucogranite-HF-H2O system. This indicates the following points: (i) Fluorite, light-colored muscovite and cassiterite can crystallize directly from the Li-F-rich gran-itic melt. (ii) The coexistence of dark-colored micas (e.g. biotite) and light-colored micas (e.g. lithium muscovite and ferromuscovite) suggests that the muscovite granite and two-mica granite can be formed under magmatic condition. The zonal texture of micas is not the sole feature for the micas of hydrothermal origin. (iii) As crystallization proceeds, the SiO2 concentration of the residual melt decreases, while the Al2O3 and F concentrations and A/CNK, NKA/Si ratios of the melt incerese, favoring the formation of Li-F-rich granites. Our experiment results are well con-sistent with the vertical zonation widely observed in rare metal bearing granites, and therefore provide strong experimental evidence for magmatic origin of Li-F-rich granite.

关 键 词：FLUORITE lithium muscovite ferromuscovite CASSITERITE melt evolution Li-F-rich granite high P-T experiment DOI: 10.1360/03yd0339 

分 类 号：P588.1[天文地球—岩石学]