Experimental study on dehydration melting of natural biotite-plagioclase gneiss from High Himalayas and implications for Himalayan crust anatexis

Here we present the results of dehydration melting, melt morphology and flu id migration based on the dehydration melting experiments on natural biotit e-plagioclase gneiss performed at the pressure of 1.0-1.4 GPa, and at the t emperature of 770-1028 degreesC. Experimental results demonstrate that: (i) most of melt tends to be distributed along mineral boundaries forming "mel t film" even the amount of melt is less than 5 vol%; melt connectivity is c ontrolled not only by melt topology but also by melt fraction; (ii) dehydra tion melting involves a series of subprocesses including subsolidus dehydra tion reaction, fluid migration, vapor-present melting and vapor-absent melt ing; (iii) experiments produce peraluminous granitic melt whose composition is similar to that of High Himalayan leucogranites (HHLG) and the residual phase assemblage is Pl+Qz+Gat+Bio+Opx +/- Cpx+Ilm/Rut +/- Kfs and can be c omparable with granulites observed in Himalayas. The experiments provide th e evidence that biotite-plagioclase gneiss is one of source rocks of HHLG a nd dehydration melting is an important way to form HHLG and the granulites. Additionally, experimental results provide constraints on determining the P-T conditions of Himalayan crustal anatexis.