高岭石的高温高压相图及其地学意义

 用阻抗匹配法和PZT压电探针技术，在100 GPa的冲击压力范围内测量了初始密度分别为1.375 g/cm³和2.001 g/cm³两种孔隙度叙永石样品的Hugoniot状态方程。根据其p_H-ρ_H线所给出的高温高压相变点，用Grüneisen状态方程计算其相变点压力所对应的温度，并结合常压下受热相变的温度值，建立了“高岭石/Al₂O₃+SiO₂+H₂O”的温度-压力相平衡图。通过该相图与线性地热线的交点推断：高岭石至少可在上地幔50 km深处作为一种含水（OH^-）矿物而稳定存在；或在俯冲板块中至少于133 km深处作为一种含水（OH^-）泥质沉积物的过渡相而存在。

PHASE DIAGRAM OF HALLOYSITE UNDER HIGH PRESSURE AND TEMPERATURE AND ITS GEOPHYSICAL IMPLICATIONS

Hugoniot measurements for halloysite with two different initial densities have been performed at the shock pressures up to about 100 GPa. Three distinct regions appear along their Hugoniots. For the samples of ρ₀=1.375 g/cm³, a low-pressure phase (LPP) exists within the shock pressure up to about 12.69 GPa, a mixed phase region (MP) begins at 12.69 GPa and ends at about 22.90 GPa, and then a high-pressure phase (HPP) occurs at shock pressures between 22.90 GPa and 46.64 GPa. The fitted linear D-u relations of its LPP and HPP can be expressed respectively as D=0.24+1.89u and D=2.47+1.12u, D is the shock wave velocity and u is the particle velocity (km/s). For the samples with ρ₀=2.001 g/cm³, the pressure ranges of its LPP, MP are covering 0~35.77 GPa, 35.77~95.48 GPa, respectively, and no HPP obviously shows on its Hugoniot. The fitted linear D-u relations of its LPP and MP are D=1.73+1.72u and D=2.69+1.37u , respectively. p-T phase boundary is determined approximately by the Mie-Grüneisen Equation of state using the present parameters. It is compared with the linear geothermal lines of 10 ℃/km and 4 ℃/km, and suggested that halloysite may be stable at depth about 50 km inupper mantle or as a transient phase in subducting slabs at depth of about 133 km.