Measurement of P-Wave Velocities in Rocks of Qinling and North China: Its Applications for the Crustal Low Velocity Layers

摘要

The crustal low velocity layers (CLVL) occuring in the middle-lower crust have been found in many regions around the world and have been explained in different ways. In this paper, the compressional wave velocities (VP) of 138 rock samples selected from Qinling and North China were measured under high temperatures (up to 1500 °C) and high pressures (up to 3 GPa) simultaneously. The general feature of the experimental data were discussed and the Vp decrease phenomenon (54 samples involved) were found. Detailed studies, mineral constitutions and textures of experimental products examined by microscope and EPMA, indicated that the dehydration, phase transition and partial melt of water-bearing minerals (hornblende and biotite), are responsible for the VP decrease. The results suggest that dehydration melting of hydrous minerals might be an important mechanism for CLVL observed in the continental crust of the study area and probably other parts of the world.