Experimental Studies on the interaction between crustal deformation and geo-fluids

孔隙空间中的H2O流体、晶界中的薄水膜以及少量溶解在晶体中的水对地壳岩石的流变特性有显著影响。为了研究水对地壳变形的影响，我们在静冈大学安装了一个固体介质变形仪（MK65S），建立了在高达1GPa和1000度的高压高温条件下获得高分辨率力学数据的实验技术。采用玛瑙和蛇纹石（主要成分为反高岭石）柱状试样进行恒应变速率实验。两种样品在高温下都会释放游离水。玛瑙样品重结晶为石英集合体，表现出稳态蠕变行为。再结晶石英精矿的c轴织构向压缩轴移动，表明受应变能驱动的晶界迁移的影响。采用傅里叶红外显微法测定了高PT实验前后样品含水量的变化。在500℃、700℃、低于和高于脱水反应温度的条件下，在800MPa围压下对蛇纹岩进行了变形实验。样品被银管和银盘包裹。部分样品在静态条件下700C或750C预热0.5-1小时。在高温（700C）下，蛇纹石表现出剧烈的弱化和蠕变行为，而在低温（500C）下，即使差应力达到1GPa，蛇纹石也不会屈服。与脱水反应有关的孔隙的形成和塌陷可能是蛇纹岩脆性-韧性转变的原因。认为蛇纹岩的脱水作用在触发双地震带板内地震中起重要作用。

Rheological properties of crustal rocks are significantly affected by H2O fluids in the pore spaces, thin water films in the grain boundaries, and a small amount of water that dissolved in crystals. In order to investigate the effects of water on crustal deformation, we set up a solid-medium deformation apparatus (MK65S), installed at the the Shizuoka University, and established experimental techniques to obtain high-resolution mechanical data at high-pressure and high-temperature conditions up to 1GPa and 1000 degrees. Constant strain-rate experiments were conducted by used cylindrical samples of agates and serpentinites (mainly composed of antigolite). Both samples release free water at elevated temperatures. Agate samples recrystallized into quartz aggregates and exhibit steady-state creep behaviors. The c-axis fabrics of recrystallized quartz concentrate to the compression axis, suggesting the effects of strain energy-driven grain boundary migration. The change of water contents in the sample before and after high PT experiments was measured by a FTIR microscopy. Deformation experiments of serpentinite were performed at 800MPa confining pressure at 500 C and 700 C, below and over the temperature of dehydration reaction, respectively. The samples were jacketed by Ag tubes and disks. Some samples were pre-heated at 700C or 750C for 0.5-1 hours under static conditions. At high-temperature runs (700C), serpentinite shows drastic weakening and creep behaviors, whereas it does not yield at the low-temperature run (500C), even when differential stress reaches to 1GPa. Formation and collapse of pores associated with dehydration reaction may be responsible to the britte-ductile transition of serpentinites. It is suggested that dehydration of serpentinites plays important roles in triggering intra-slab earthquakes in the double seismic zones.