不同温压条件下蛇纹岩和角闪岩中波速与衰减的各向异性

在实验室中研究了蛇纹岩和角闪岩样品在不同温压条件下的纵、横波速度和Q值．这两种岩样对应的主要组成矿物叶蛇纹石和普通角闪石都具有很强的晶格优选方位（LPO）．随着围压的增加，波速和Q值均增大，但是在相互正交的三个方向上（垂直或平行于层理面及线理方向）增大的速度并不相同，这与微裂隙的逐渐闭合密切相关．在600MPa的围压下升高温度直到600℃以上，由于微裂隙的热扩张受到约束，波速和Q值下降幅度很小．观测到的波速和Q值的各向异性具有不同的机理，波速各向异性主要与定向分布的微裂隙和主要矿物的LPO等构造因素有关；高围压下纵波Q值各向异性与速度各向异性正好相反，可能是由于形成层理面的定向排列的平板状矿物晶体沿不同方向边界之间接触程度不同造成的．

VELOCITIES AND ATTENUATION OF P-AND S-WAVES AND THEIR ANISOTROPIES IN SERPENTINITE AND AMPHIBOLITE UNDER DIFFERENT P-T CONDITIONS

Velocities and Q values of P-and S-waves had been measured for an amphibolite and a serpentinite under different pressures and temperatures. Both rocks show a strong lattice prefered orientation (LPO) of the major minerals hornblende and antigorite. Velocities and Q values increase with pressure, with the rate being different in the three orthogonal directions (normal and parallel to foliation and lineation) and closely related to the progressive closure of microcracks. Increase of temperature under600MPa's confining pressure up to more than 600oC decreases velocihes and Q values only slightly since thermal cracking is prevented by the pressure. The anisotropy of velocities and Q values of P- and S-waves in both rocks is found to be different by nature. The anisotropy of wave velocities is the highest at low confining pressures and is caused by oriented microcracks and the LPO of major minerals. Increase of confining pressure decreases the velocity anisotropy at a smaller and smaller rate. The residual anisotropy of velocities under high confining pressures is mainly caused by preferred mineral orientation. By contrast,the anisotropy of Q is very small under low pressures and markedly enhanced as confining pressure increases. Under high pressures,the anisotropy of Qp is reversed from that of P-wave velocities:Qp is the highest whereas Vp is the lowest in the direction normal to the foliation. The generation of the pronounced anisotropy of Qp by increasing pressure is due to the directional dependent increase of contact areas on the oriented grain boundaries of the platy minerals forming the foliation plane. The increase of Q with confining pressure in the direction normal to foliation plane is a result of the decrease of damping caused by compressive strain related to that caused by shear strain. The reverse is true for X and Y directions parallel to foliation plane in sepentinite and X direction parallel to lineation in amphibolite.