俯冲带绿泥石高温高压流变学实验研究

Chlorite is one of the critical hydrous minerals in subduction zones, and its rheological properities are very important for understanding the dynamics of subduction zone. It is speculated that chlorite is much weaker than other mantle minerals, thus it could control the mechanical decoupling between the subducting slab and the mantle wedge. In addition, The developed fabric of chlorite could contribute to the trench parallel seismic anisotropy in many subduction zones. However, the mechanical properties of chlorite have not been quantified, which strongly limits our understanding toward the dynamics of subduction zones. This project is planning to conduct high temperature and high pressure deformation experiment on chlorite at 1-3 GPa, 500-700 oC and strain rate of 10-6-10-4 s-1, by using 5 GPa Griggs apparatus. Then, the chlorite deformation fabrics and deformation mechanism will be analyzed by using high resolution EBSD. Chlorite deformation constitutive equation and developed fabrics will be acquired in this project. According to the deformation mechanical data, the decoupling mechanism between subducting slab and mantle wedge will be explored. At the same time, based on the developed chlorite fabrics and elastic parameters, the seismic anisotropy induced by deformed chlorite will be modeled and discussed.

作为俯冲带关键含水矿物之一，绿泥石的流变学性质对于俯冲带地球动力学过程具有重要影响。绿泥石流变学强度被认为远小于地幔其他常见矿物，可能是引起板楔解耦的关键；发育强组构的绿泥石对俯冲带剪切快波平行海沟地震波各向异性特征具有重要贡献。然而目前国际上对于绿泥石低流变学强度的关键作用，仅限于天然样品研究结果的推测，缺少直接的高温高压流变学实验数据支持。本项目拟主要利用5GPa高温高压流变仪，在1-3 GPa、500-750 oC及10-6-10-4 s-1条件下，对绿泥石多晶集合体开展高温高压变形实验研究；并结合高精度背散射衍射（EBSD）技术，分析绿泥石变形组构特征及机制。实验拟获取绿泥石流变本构方程及变形发育的组构特征。根据绿泥石变形力学结果，探讨俯冲带板楔解耦机制；根据绿泥石发育组构特征，并结合绿泥石弹性参数，模拟计算俯冲带温压条件下绿泥石变形组构导致的地震波各向异性特征。

作为俯冲带关键含水矿物之一，绿泥石的流变学性质对于俯冲带地球动力学过程具有重要影响。绿泥石流变学强度被认为远小于地幔其他常见矿物，可能是引起板楔解耦的关键；发育强组构的绿泥石对俯冲带剪切快波平行海沟地震波各向异性特征具有重要贡献。围绕这些关键问题，本项目对绿泥石多晶集合体进行了相关高温高压流变学实验。（1）轴向压缩实验结果表明，绿泥石在1-2.5 GPa、500-700 oC以及1*10-4-1*10-5/s的实验条件下以位错蠕变方式变形并产生稳态蠕变，获得其幂流变方程为。相同变形条件下，绿泥石屈服强度明显低于叶蛇纹石屈服强度。与橄榄石多晶集合体及洋壳榴辉岩相比，绿泥石流变学强度明显低于两者。因此推测，在俯冲带，俯冲板片与地幔楔之间的含绿泥石橄榄岩及绿泥石富集层可能会承担主要应变，从而导致板片与地幔楔发生解耦。（2）剪切实验研究表明，随着温度增加，绿泥石[100]及[010]在平行剪切方向呈大圆环分布。绿泥石晶内变形分析表明，其变形形成以[001]轴为旋转轴的扭转颗粒边界以及对应启动滑移系分别为[100](001)、[010](001)和[hk0](001)的倾斜颗粒边界。高温下虽然绿泥石有多个滑移系启动，但不同滑移系临界剪切应力差别不大。绿泥石附着板片变形形成的强[hk0](001)组构可以解释某些大角度俯冲带地幔楔存在大延时地震波各向异性特征。