中国科学院地球化学研究所机构知识库

In situ measurements of elastic wave velocities and electrical conductivities in the three structural directions (normal to foliation Z, perpendicular to lineation in foliation Y and parallel to lineation X) for an amphibolite collected from southwestern margin of the Tarim Basin, northwest China, were carried out in the laboratory. The elastic wave velocity was measured with the combined transmission-reflection method at pressures up to 1.0 GPa (at room temperature) and temperatures up to 700 degrees C (at 1.0 GPa) and the electrical conductivity was measured with the impedance spectroscopy from 250 to 700 degrees C at 1.0 GPa. The experimentally determined data included compressional (V(p)) and shear wave velocities (V(s)), velocity anisotropy (A(v)), intrinsic pressure and temperature derivatives of V(p) and V(s), electrical conductivity (sigma), electrical conductivity anisotropy (A sigma) and the parameters of the Arrhenius relationship. Elastic wave velocities increase in the structural directions Z, Y, X, with V(p) of 6.63, 6.78 and 6.95 km s(-1) and V(s) of 3.75, 3.82 and 3.96 km s(-1) for Z, Y and X, respectively, at pressure of 1.0 GPa. Elastic wave velocities increase linearly with pressure at room temperature and pressures between 0.25 and 1.0 GPa and decrease linearly with increasing temperature at 1.0 GPa. The pressure coefficients of the sample are in the range of 0.1883-0.2308 km s(-1) GPa(-1) for V(p) and 0.1149-0.1678 km s(-1) GPa(-1) for V(s). The temperature coefficients are in the range of 2.09-2.35 x 10(-4) km s(-1) GPa(-1) for V(p) and 1.28-1.68 x 10(-4) km s(-1) GPa(-1) for V(s). The electrical conductivity increases with increasing temperature, consistent with the Arrhenius relationship. Activation energies for the three structural directions of the amphibolite are in the range of 0.71-0.75 eV. The amphibolite shows velocity anisotropy (4.15-4.86 per cent for V(p) and 5.29-5.84 per cent for V(s) at 0.25-1.0 GPa) and electrical conductivity anisotropy (11.1-25.2 per cent). Based on the regional crust model and geothermal gradient, velocity and electrical conductivity-depth profiles were calculated for the sample. These profiles were then compared with those derived from seismic reflection/refraction data and from electromagnetic data. Our results showed that the amphibolite sample has V(p) and V(s) in agreement with those of the middle and lower crust obtained from seismic reflection/refraction data, and sigma in accord with that of the lower crust deduced from electromagnetic data. The lower crust of the electromagnetic crust model is roughly equivalent to the middle and lower crust layers of the seismic crust model. Therefore, it is suggest that the amphibolite may be one of the constituents of the present middle and lower crust in the Tarim Basin.