KINETICS OF PRESSURE SOLUTION AT HALITE-SILICA INTERFACES AND INTERGRANULAR CLAY FILMS
KINETICS OF PRESSURE SOLUTION AT HALITE-SILICA INTERFACES AND INTERGRANULAR CLAY FILMS
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DOI：
10.1029/95jb00911
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发表时间：
1995-07-10
影响因子：
3.9
通讯作者：
EVANS, B
中科院分区：
文献类型：
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作者：
HICKMAN, SH;EVANS, B
压溶作用被广泛认为是沿地壳断裂和成岩作用的一种潜在的重要变形机制，但其机制和动力学仍存在很大争议。为了更好地了解在颗粒到颗粒尺度上控制压力溶解速率的基本因素，我们进行了在盐水中将凸形岩盐透镜压在熔融二氧化硅平板上的实验。流体压力维持在0.1兆帕；温度和平均接触法向应力分别为8.3-90.2摄氏度和0.5-13.5兆帕。使用反射光干涉法和透射光显微照相技术监测两个镜片之间接触斑点的几何形状和生长速度以及镜片彼此接近(会聚)的速度。当盐岩和二氧化硅透镜在盐水中被压在一起时发生会聚(盐岩/二氧化硅实验)。没有观察到底切，干控制实验表明位错蠕变可以忽略不计。在50.2摄氏度的实验中，收敛速度从0.01到0.05微米/天不等，这取决于平均法向应力和接触点半径。这些数据与晶间压力溶液受扩散系数很高(类似于10(-5)-10(-7)cm(2)/S)的晶间薄膜扩散的速率限制相一致。数据进一步表明，该薄膜的扩散系数和/或厚度随法向应力的减小而增加，至少对于小于约4 Mpa的法向应力是如此。由于没有观察到岛屿-海峡边界结构，我们认为该薄膜由连续的一层强吸附(即结构)的水组成，在变形过程中保持在盐岩和二氧化硅透镜之间。在0.11 N的恒定负载下，但在8.3度、50.2度和90.2℃的恒定负载下进行的类似实验中，在给定法向应力和接触点大小时，收敛速度大致恒定。这种温度不敏感的原因尚不清楚，但可能是由于相界结构或厚度随着温度的升高而变化，足以抵消预期的热激活。还进行了一项实验，将盐岩透镜压在熔融二氧化硅平板上，表面涂有一层0.8亩厚的钠基蒙脱石盐膜。在相同的载荷和温度下，这种粘土薄膜产生的收敛速度比在没有粘土的盐岩/二氧化硅实验中观察到的速度增加了大约五倍。IPS速率对接触斑点半径和沿晶界存在第二相的强烈敏感性表明，细粒、富粘土的断层泥和多相颗粒集合体在中上地壳特别容易受到压力溶液蠕变的影响。
Pressure solution is widely regarded as a potentially important deformation mechanism along crustal faults and during diagenesis, yet the mechanisms and kinetics of this process remain highly controversial. To better understand the fundamental factors controlling the rates of pressure solution at the grain-to-grain scale, we conducted experiments in which convex halite lenses were pressed against flats of fused silica in brine. Fluid pressures were maintained at 0.1 MPa; temperatures and mean contact normal stresses ranged from 8.3 degrees to 90.2 degrees C and 0.5 to 13.5 MPa, respectively. The geometry and growth rate of the contact spot between the two lenses and the rate at which the lenses approached one another (convergence) were monitored using reflected light interferometry and transmitted light photomicrography. Convergence occurred when halite and silica lenses were pressed together in brine (halite/silica experiments). No undercutting was observed, and dry control experiments indicated negligible dislocation creep. Convergence rates in experiments at 50.2 degrees C ranged from 0.01 to 0.05 mu m/d, depending on mean normal stress and contact spot radius. The data are consistent with intergranular pressure solution (IFS) rate-limited by diffusion through an intergranular film with a very high diffusion coefficient (similar to 10(-5)-10(-7) cm(2)/s). The data further suggest that the diffusion coefficient and/or thickness of this film increases with decreasing normal stresses, at least for normal stresses less than about 4 MPa. As no island-channel boundary structures were observed, we propose that this film consists of a continuous layer of strongly adsorbed (i.e., structured) water that is maintained between the halite and silica lenses during deformation. Convergence rates in similar experiments conducted at a constant load of O.11 N but at 8.3 degrees, 50.2 degrees, and 90.2 degrees C were approximately constant at a given normal stress and contact spot size. The cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation. An experiment was also conducted in which a halite lens was pressed against a fused silica flat coated with an 0.8-mu m-thick film of Na-montmorillonite in brine. This clay film produced an approximately fivefold increase in convergence rates over those observed in a halite/silica experiment conducted without clay at the same load and temperature. The strong sensitivity of IPS rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine-grained, clay-rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust.