新疆东准噶尔花岗岩类岩石高温高压弹性波速度及其对地壳结构的约束

The elastic wave velocities of the granitoids from Eastern Junggar of Xinjiang at high temperature and high pressure and their geological constraints on the crustal structure

应用超声波反射一透射法,在最高压力为1.0 GPa(室温),最高温度为700℃(1.0 GPa)的条件下对新疆东准噶尔地区的卡拉麦里花岗岩带和野马泉岩体的典型花岗岩类岩石(碱长花岗岩、碱性花岗岩、花岗闪长岩、二长花岗岩和石英闪长岩)的纵波速度(V_p)和横波速度(Vs)进行了测量.结果显示,在常温、压力0.4~1.0 GPa条件下,东准噶尔地区花岗岩类岩石的V_p和V_s均随压力呈线性增加,说明在这个压力段岩石中的微裂隙已基本闭合.室温、1.0 GPa时花岗岩类岩石的V_p是5.79~6.84 km·s^(-1),V_s是3.26~3.85 km·s^(-1).依据压力与V_P及压力与V_s的线性关系,拟合得到常温常压下花岗岩类岩石的纵波和横波压力系数分别是0.1568~0.4078 km/(s·(GPa)和0.0722~0.3271 km/(s·GPa),V_(p0)和V_(s0)分别是5.62~6.47 km·s^(-1)和3.15~3.75 km·s^(-1).恒压1.0 GPa、室温到700℃条件下,花岗岩类岩石的V_p和V_s均随温度的升高呈线性降低,温度系数分别为(—3.41^-4.96)×10^(-4)km/(s·℃)和(—0.88~—3.22)×10^(-4)km/(s·℃).利用实验获得的花岗岩类岩石的V^(p0)、V^(s0)及温度系数和压力系数,结合东准噶尔地区的地热资料,建立了V_p和V_s随深度变化的剖面.将获得的V_p和V_s-深度剖面与该区地球物理探测结果对比,发现东准噶尔地区的碱长花岗岩、碱性花岗岩、二长花岗岩和部分花岗闪长岩的V_p和V_s与该区上地壳速度吻合很好,同时这几种岩石的平均泊松比也与上地壳泊松比一致,因此我们认为这几种类型的岩石是该区上地壳的重要组成部分.另外,石英闪长岩的V_p和V_s均符合中地壳的速度,可能为中地壳中的一种岩石.

The compressional （Vp） and shear wave velocities （Vs） of typical granitoids （alkali- feldspar granite, alkaline granite, granodiorite, monzogranite and quartz diorite） from Kalamaili granite belt and Yemaquan body in Eastern Junggar, Xinjiang were experimentally measured at pressures up to 1.0 GPa （room temperature） and temperatures up to 700 ℃ （1.0 GPa） by ultrasonic reflection-transmission method. The results show that both Vp and Vs of the granitoids present a linear velocity increase with the pressure at room temperature from 0. 4∽ 1.0 GPa, which is interpreted in terms of closure of the microcracks in rocks under this pressure range. The Vp and Vs of the granitoids are 5.79∽6.84 km·s-1 and 3.26∽3.85 km ·s-1 respectively at room temperature and 1.0 GPa. On the basis of the linear relationship between pressure with Vp and Vs, we derived the pressure derivatives of Vp and Vs as 0. 1568∽0. 4078 km/（s· GPa） and 0.0722∽0. 3271 km/（s· GPa） respectively, and the reference velocities Vp0 and Vs0 are 5.62-- 6.47 km ·s-1 and 3.15∽3.75 km ·s-1 respectively. At 1.0 GPa, Vp and Vs of the granitoids show a linear decrease with temperature from room temperature to 700 ℃, and temperature derivatives of velocities are （--3. 41∽-4. 96）×10.4 km/（s· ℃） and （--0.88∽--3. 22）× 10.4 km/（s· ℃）, respectively. Taking advantage of derivatives of velocities and reference velocities of the granitoids obtained from our experiments, and combining regional geothermal resources of East Junggar area, Vp and Vs-depth profiles were calculated. From the comparison of velocity-depth profiles with geophysical exploring results, we infer that the Vp and Vs of the alkali-feldspar granite, alkaline granite, monzogranite and part of granodiorite in Eastern Junggar of Xinjiang are coherent well with the velocity of the upper crust, and the average Poissonrs ratio of several rocks are also consistent with the Poissonts ratio of the upper crust. Therefore, we suggest that these kinds of rocks are important parts of the upper crust in this region. In addition, the Ve and Vs of the quartz diorite are both in accord with the middle crust, suggesting that it may be one kind of rocks in the middle crust of this region.