西藏南部花岗岩类熔化实验的初步研究

PRELIMINARY EXPERIMENTAL STUDY ON THE MELTING OF GRANITES IN SOUTHERN XIZANG

Melting experiments have been carried out on major rock types from the three rock belts in Southern Xizang. These rocks, being quite different in chemical composition, are representative of granites of Late Yenshanian, Early Himalayan and Late Himalayan periods in this area, Experimental water pressures are eontrolled at 2kb. Results show the beginning temperatures of melting for the seven rock types are : Gubug tourmaline-muscovite granite 615℃, Zayu coarse-grained gneiesose biotite-granite 635℃, Kangmar finegrained gneissose two-mica granite 640℃,Dala gneissese two-mica granite 645℃, Quxu biotite granite 660℃, Lhasa granodiorite 700℃, and Gyubge hypersthene diorite 740℃. The beginning temperature of melting decreases with decreasing granite age.Spatially the temperature of formation drops progressively southwards from Kangdese through Lhagoi Kangri to Himalaya rock belt. Additionally, the beginning temperature of melting varies with the contents of mafic minerals and differentiation index of the rocks. Our experimental and geological data suggest that the three rock belts in Southern Xizang are all of magmatic origin. Himalaya and Lhagoi Kangrl rock belts arc stemed from partial melting of continental material, whereas Kangdese rock belt probably from remelting or partial melting of oceanic crustal material.

Melting experiments have been carried out on major rock types from the three rock belts in Southern Xizang. These rocks, being quite different in chemical compo-sition, are representative of granites of Late Yenshanian, Early Himalayan and Late Himalayan periods in this area.Experimental water pressures are controlled at 2kb. Results show the beginning temperatures of melting for the seven rock types are: Gubug tourmaline-muscovite granite 615℃, Zayu coarse-grained gneissose biotite-granite 635℃, Kangmar fine-grained gneissose two-mica granite 640℃,Dala gneissose two-mica granite, 645 ℃ Quxu biotite granite 660℃, Lhasa granodiorite 700℃, and Gyubge hypersthene diorite 740℃.The beginning temperature of melting decreases with decreasing granite age. Spatially the temperature of formation drops progressively southwards, from Kangdese through Lhagoi Kangri to Himalaya rock belt. Additionally, the beginning temperature of melting varies with the contents of mafic minerals and differentiation index of the rocks.Our experimental and geological data suggest that the three rock belts in Southern Xizang are all of magmatic origin. Himalaya and Lhagoi Kangri rock belts are stemed from partial melting of continental material, whereas Kangdese rock belt probably from remelting or partial melting of oceanic crustal material.