Yang et al., 2001 experimental melting himalaya

Yang et al., 2001 experimental melting himalaya -...

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Experimental study on dehy- dration melting of natural biotite-plagioclase gneiss from High Himalayas and implica- tions for Himalayan crust anatexis YANG Xiaosong 1,2 , JIN Zhenmin 1 , Ernst Huenges 2 , Frank R. Schilling 2 & Bernd Wunder 2 1. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China; 2. GeoForschungsZentrum, Potsdam, D-14473, Germany Abstract Here we present the results of dehydration melting, melt morphology and fluid migration based on the dehydration melting experiments on natural bio- tite-plagioclase gneiss performed at the pressure of 1.0 ü 1.4 GPa, and at the temperature of 770 ü 1028 ć . Experimental results demonstrate that: ( ν ) most of melt tends to be dis- tributed along mineral boundaries forming “melt film” even the amount of melt is less than 5 vol%; melt connectivity is controlled not only by melt topology but also by melt fraction; ( ξ ) dehydration melting involves a series of subprocesses including subsolidus dehydration reaction, fluid migration, vapor-present melting and vapor-absent melting; ( ο ) ex- periments produce peraluminous granitic melt whose com- position is similar to that of High Himalayan leucogranites (HHLG) and the residual phase assemblage is Pl+Qz+ Gat+Bio+Opx r Cpx+Ilm/Rut r Kfs and can be comparable with granulites observed in Himalayas. The experiments provide the evidence that biotite-plagioclase gneiss is one of source rocks of HHLG and dehydration melting is an im- portant way to form HHLG and the granulites. Additionally, experimental results provide constraints on determining the P-T conditions of Himalayan crustal anatexis. Keywords: gneiss, dehydration melting, melt topology, fluid migra- tion, leucogranite, granulite, Himalayas. The process of partial melting due to the breakdown of hydrous minerals but without any additional free water is believed to be the most important mechanism for crustal anatexis, because it seems to be true that the amount of H 2 O available in the middle or/and lower crust is, in most cases, proposed to be very small. In literature the mecha- nism of crustal anatexis is described as dehydration melt- ing [1] or vapor-absent melting [2] . Current understanding of the process is mainly attributed to extensive experimental investigations on synthetic or natural powdered speci- mens [1 ü 6] . However, changing the textures of rocks by smashing natural rocks may lose some significant infor- mation of experimentally induced melt textures. Recently, researchers pay more attention gradually to the melting experiments on natural rocks as starting materials. Al- though it is not believed that the melt-mineral-system could completely attain equilibrium within experimental time scale due to relatively large mineral grain sizes, it has been shown that dehydration melting experiments on natural rocks provide valuable data for understanding of melting, melt topology and fluid migration [7 ü 9] . The knowledge of High Himalayan leucogranites (HHLG) plays a fundamental role in the understanding of crustal evolution during the post-collision period. Although many
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This note was uploaded on 03/19/2012 for the course GEOLOGY 6 taught by Professor Rm during the Spring '12 term at UNAM MX.

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Yang et al., 2001 experimental melting himalaya -...

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