Experimental deformation of partially molten Westerly granite under fluid‐absent conditions, with implications for the extraction of granitic magmas
Experimental deformation of partially molten Westerly granite under fluid‐absent conditions, with implications for the extraction of granitic magmas
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DOI：
10.1029/94jb03388
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发表时间：
1995-08
影响因子：
--
通讯作者：
E. Rutter;D. H. K. Neumann
中科院分区：
文献类型：
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作者：
E. Rutter;D. H. K. Neumann
通过恒应变速率、蠕变和应力松弛试验，研究了部分熔融西风花岗岩在800° ~ 1100 ° C、250 MPa围压下的力学行为。样品中唯一的水来自含水相、黑云母、微量硅铝石和白云母的分解以及硅铝石的蚀变产物。因此，熔体的量由测试温度控制，范围为800°C下的3%至1100°C下的50%。在该温度范围内，强度从2500 MPa下降到小于1 MPa，并获得了部分熔融岩石的初步本构流动定律，以允许外推到低应变率。在950° C和1000°C下，根据在已知压力梯度下可以使熔体渗透到多孔砂中的距离，估计单独熔体的比较粘度。在所有条件下，固体颗粒基体的变形仅以脆性断裂方式发生。含有高达10体积%的熔体的样品失败的剪切断层带的形成。在较高的熔体分数，熔体填充的“孔隙”崩溃的剪切增强压实，挤压熔体进入轴向裂纹。高于40体积%的熔体，未断裂的固体颗粒被被动地携带在流动的液体中。在该体系中没有“流变临界熔体百分比”的证据。类比单轴压实的水饱和的土壤，一个简单的模型是建立描述一个两阶段的过程中提取的花岗岩熔体从他们的原岩与非静水应力的帮助。剪切增强压实被推断为驱动熔体到网络的熔体填充的静脉，于是通过高渗透性静脉网络的多孔流允许熔体快速排水到更高的地壳水平。
The mechanical behavior of partially molten Westerly granite was investigated in the temperature range 800°–1100°C, 250 MPa confining pressure, by means of constant strain rate, creep, and stress relaxation tests. The only water in the samples came from the breakdown of hydrous phases, biotite, minor chlorite and muscovite and alteration products of feldspars. Thus the amount of melt was controlled by the test temperature and ranged from 3% at 800°C to 50% at 1100°C. Over that temperature range, strength decreased from ≈500 MPa to less than 1 MPa, and a preliminary constitutive flow law for the partially molten rock was obtained to allow extrapolation to low strain rates. The comparative viscosity of the melt alone was estimated at 950° and 1000°C from the distance it could be made to penetrate into a porous sand under a known pressure gradient. Under all conditions, deformation of the matrix of solid grains was by brittle fracture only. Samples containing up to 10 vol % melt failed with the formation of a shear fault zone. At higher melt fractions, melt-filled “pores” collapsed by shear-enhanced compaction, squeezing the melt into axial cracks. Above 40 vol % melt, unfractured solid grains were carried about passively in the flowing liquid. There was no evidence of a “rheologically critical melt percentage” in this system. By analogy with the uniaxial compaction of water-saturated soils, a simple model is erected to describe a two-stage process for the extraction of granitic melts from their protoliths with the aid of nonhydrostatic stress. Shear-enhanced compaction is inferred to drive melt into a network of melt-filled veins, whereupon porous flow through the high-permeability vein network allows rapid drainage of melt to higher crustal levels.