Origin of Li-F-rich granite: Evidence from high P-T experiments |
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Authors: | Email author" target="_blank">Li?Fuchun?Email author Jinchu?Zhu Bing?Rao Zhangdong?Jin Linsong?Zhang |
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Institution: | 1. School of Resource and Environment Sciences, Nanjing Agriculture University, Nanjing 210095, China;State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, 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 |
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Abstract: | 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. |
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Keywords: | fluorite lithium muscovite ferromuscovite cassiterite melt evolution Li-F-rich granite high P-T experiment |
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