汶川地震断裂带水岩相互作用及其对断裂带演化影响

汶川地震断层岩的矿物学和地球化学特征揭示出地震断层经历了漫长时间演化和复杂的水岩相互作用.间震期水岩相互作用导致断层岩中的破碎矿物蚀变，尤其是长石等矿物含量渐渐减少甚至消失，而黏土矿物（蒙脱石、伊利石、伊/蒙混层、绿泥石等）含量逐渐增高，以及如黄铁矿、石膏、重晶石、坡缕石等热液系统中常见的矿物大量出现；Mg、P、Ti、Mn、Fe等元素倾向富集在断层带中，而Si、K和Na等出现明显的亏损；元素的大量迁移导致断层带的体积巨量亏损.实验结果表明，黏土矿物的亲水性引起水渗透率比干燥气体渗透率明显偏低，并且二者偏差无法通过Klinkenberg校正消除.蒙脱石吸水膨胀和黏土矿物颗粒表面吸附孔隙流体造成孔隙度降低是导致水渗透率偏低的重要原因.断层岩碎屑结构使得其中的孔隙可能在600 MPa围压下得以保存，从而有助于流体沿断层带下渗，并在断层带深部形成高流体孔隙压.地震断层的主要矿物学及粒度分布特征并非在地震破裂过程中形成，因此利用断层岩粒度分布资料估算地震破裂能并不合适.

Fluid-rock interactions and their effects on the evolution of the Wenchuan earthquake fault zone

Mineralogical and geochemical results of the Wenchuan earthquake fault rocks reveal long-term evolution and fluid-rock interactions in the fault zone. Interseismic fluid-rock interaction altered the fault rocks and results in the depletion of felsic minerals and precipitation of clay minerals (smectite, illite, mixed layers of illite and smectite and chlorite). Hydrothermal minerals, such as pyrite, gypsum, barite and palygorskite, are widely present in the fault zone. The fault rocks are rich in Mg, P, Ti, Mn and Fe, but deplete Si, K and Na elements. Mass remove of fault rocks lead to significant volume loss in the fault zone. Experimental results indicate that gas permeability of fault rocks is higher than that measured by water, being attributed to the hydrophilic property of clay minerals, which lead to the reduction of effective pore space and thereby lowering permeability. Pores in fault rocks can withstand confining pressure up to 600 MPa, implying that fluids at depths may be sealed to build up excess pore pressure. Fluid alteration modified the mineralogy and particle size distribution of fault rocks, and therefore it is not applicable to estimate the rupture energy of earthquake by particle size distribution data.