长英质麻粒岩的高温高压流变学实验研究

Felsic granulite is the major component in the upper and middle continental lower crust. The rheological properties of felsic granulite are of great significance for understanding a certain continental dynamical processes, such as coupling and decoupling deformation between the crust and the upper mantle, and uplift of plateau. However, few efforts have been made toward understanding the rheological behavior of felsic granulite. This study will perform systematic high temperature and pressure rheological experiments on felsic granulite using a 5GPa modified apparatus, aiming to investigate the rheological strength and establish the constitutive equation of felsic granulite under dry and wet conditions. In addition, shear deformation experiments will also be conducted to explore the fabric evolution of component minerals in felsic granulite. Combined with our previous experimental results on mafic granulite, this study will furnish more complete experimental constraints on the interpretation of continental lithosphere strength envelope, and deformation features and seismic anisotropy in the continental lower crust.

长英质麻粒岩是大陆下地壳中上部的主要岩石，其流变学性质对于壳幔耦合、高原隆升等大陆动力学过程有重要意义，但研究程度较低。本研究将采用人工合成的长英质麻粒岩作为实验起始样品，利用5GPa改进型流变仪进行系统的流变学实验，拟研究长英质麻粒岩在干条件和湿条件下的流变学强度，建立其流变学本构方程，并研究大应变剪切变形条件下矿物组构发育情况。结合申请人青年基金项目中镁铁质麻粒岩的研究成果，本研究将为探讨大陆岩石圈强度轮廓、大陆下地壳变形和地震波各向异性提供更完整的实验约束。

大陆下地壳的流变学性质具有重要地球动力学意义，但一直缺乏有效的实验约束。本项目针对代表大陆下地壳中上部的长英质麻粒岩开展高温高压流变学实验，拟建立其流变学本构方程，并探讨其流变学性质对大陆下地壳强度的启示。我们采用热压合成的长英质麻粒岩（长石66%+石英18%+辉石8%+角闪石8%）作为实验样品，进行了三个热压实验和8个成功的轴向压缩实验，建立了长英质麻粒岩的流变学本构方程：epison=10(-4.27)sigma(4.16)exp[-267000/(RT)]。这一力学数据表明我们的实验样品以位错蠕变为主导变形机制。外推到自然应变速率（10-14/s）和800C条件下，长英质麻粒岩的力学强度约为700MPa。与前人的资料对比表明，长英质麻粒岩的流变学强度比镁铁质麻粒岩的强度稍大，但仍弱于代表大陆上地幔的橄榄岩/橄榄石集合体的流变学强度，从而仍然支持果酱三明治式的大陆岩石圈强度轮廓。