PHASE TRANSFORMATION BOOSTER IN WATER DURING ULTRAHIGH-PRESSURE METAMORPHISM

doi:10.3321/j.issn:1000-2383.2001.01.003

Abstract：The calculation in the hydrostatic pressure gradient shows thatthe eclogites were formed in the depth of at least 70 km, and the coesite-bearing eclogites in the depth of at least 120km. In addition, the eclogites containing both the diamond and coesite in the depth of at least 145 km. It is unimaginable that the ultrahigh-pressure metamorphic rocks are uplifted to the earth surface from such depths. Many references show that the water is indispensable to the ultrahigh-pressure metamorphism. Based on the studies of the mineral dehydration, the geothermal curves and the phase change diagram of water, this paper indicates that such supercharges as the phase transformation booster in water greatly increase the lithostatic gradient in the process of the ultrahigh-pressure metamorphism. The depth for the formation of the ultrahigh-pressure metamorphic rocks calculated with hydrostatic pressure is only the greatest depth. However, the actual depth for the formation of the ultrahigh-pressure metamorphic rocks was much smaller than the theoretical depth as calculated with hydrostatic pressure.