冀西北万全地区大麻坪地幔岩包体高温高压弹性波研究及其地质意义

Measurements of elastic wave velocities in mantle rocks at high temperatures and high pressures from Damaping area, Wanquan, northwestern Hebei, China, and its geological significance.

对河北大麻坪碱性玄武岩及其内的辉石岩和二辉橄榄岩包体进行了不同温压条件下的弹性波速测定。结果表明,岩石波速与压力正相关,与温度负相关;相同条件下二辉橄榄岩的弹性波速最大,辉石岩次之,玄武岩最小。在1.4GPa压力下获得二辉橄榄岩和辉石岩的弹性波速分别为7.87km/s和7.47km/s,最接近壳幔过渡带的弹性波速。而现代地球物理资料显示该地区莫霍面深度为32km,认为26Ma以来,该地区发生了大规模的岩石圈减薄地质事件。

Measurements of elastic wave velocities at different high temperatures and high pressures were made on alkali basalt and xenoliths of pyroxenite and lherzolite from Damaping, Hebei. The experimental results indicate that vP increases with pressure increasing, whereas vP decreases with temperature increasing. Results indicate that the rock wave velocity vP has a positive correlation with pressure and a negative correlation with temperature. Under the same conditions, vP of lherzolite is highest, that of pyroxenite comes next and that of basalt is lowest. The vP values of lherzolite and pyroxenite obtained at 1.4 GPa are 7.87 km/s and 7.47 km/s respectively. These values are closest to that of rocks from the crust-mantle transition zone. Geophysical data indicate that the Moho depth of the area is ～32 km. The authors think that large-scale lithospheric thinning took place in the area since 26 Ma.