关键词: 华北, 结晶岩, 相平衡, 波速, 岩石级数

Abstract: Seven types of typical rock wave velocity are classified according to the relationship of mineral composition,origin of the crystalline rocks with absolute values of the wave velocities at high pressures and room temperatures, and the relationship of the wave velocities with phase assembly transformation at high pressures and high temperatures. And at a certain structural envirement, in the light of the relation of variational wave velocity of the rocks with crustal depth, we suggest the concept of rock grade which reflects acidity or basicity of rocks. Its meaning is that with the values from seismic refraction sounding at a certain depth we can have rock grades of the comprehensive rocks at the same depth. On the basis of above principles, we study the composition of the crust of North China, the generation and exsisting conditions in the crust for the amphibolite, the phase of the quartzite and generating cause of the low velocity layers in the crust.

Key words: North China, Crystalline rock, Wave velocity, Phase equilibrium, Rock grade