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野外地质观察发现,在大陆地壳变质岩中可以广泛观察到围绕一个大的单晶或者硬质点的两端区域填充低粘度相物质形成的压力影。为了定量研究岩石材料中压力影的形成条件,本文利用高精度Paterson气体介质变形装置,对含有刚性球的圣卡罗橄榄石和洋中脊玄武岩(MORB)的混合物圆柱型样品进行了高温高压扭转变形试验。变形实验前样品的初始熔融均匀分布,比例为φ≈0.05,变形试件尺寸为D8.9mm×L5.5mm,内含8粒直径约1mm的刚性球。扭转变形试验温度为1473K,围压为300MPa,应变率为γ≈1×10~(-4)s~(-1),最大剪切变形为γ≈4。实验结果表明,岩石受到扭转力的作用产生变形之后,当局部剪切应变达到γ≈1时,可以在刚性球周围形成熔融富集带和熔融贫乏带,即压力影构造,围绕刚性球对称分布。由于熔融分布的不均一性,富集带熔融比例上升,最高可以达到φ_(high)=0.1~0.3,熔融贫乏带熔融比例下降,含量为φ_(low)=0.01~0.02。由于刚性球对其周围的压力分布的扰动区域大约为刚性球的尺度范围,因此,在离开刚性球一定距离后,熔融趋于均匀分布。
Field geologic observations have found that the pressure shadow formed by filling low-viscosity phase materials at both ends of a large single crystal or hard point can be widely observed in continental crustal metamorphic rocks. In order to quantitatively study the formation conditions of pressure shadow in rock materials, a high-precision Paterson gas medium deformation device was used to perform high-temperature and high-pressure torsion deformation on a mixture of samauro-olivine and mid-ocean ridge basalt (MORB) test. Before the deformation experiment, the initial melting of the sample was uniformly distributed, the ratio was φ ≈ 0.05, and the size of the deformed specimen was D8.9mm × L5.5mm, containing 8 rigid balls with a diameter of about 1mm. The torsional deformation test temperature is 1473K, the confining pressure is 300MPa, the strain rate is γ≈1 × 10 -4 s -1, and the maximum shear deformation is γ≈4. The experimental results show that after the deformation of the rock under the action of torsional force, when the local shear strain reaches γ≈1, the melt-enriched zone and melt-depleted zone can be formed around the rigid sphere, that is, the pressure-shadow structure, symmetrically distributed around the rigid sphere . Due to the heterogeneity of the melt distribution, the ratio of enrichment zone melting increases up to φ_ (high) = 0.1-0.3, and the melt lean zone melting ratio decreases with a content of φ_ (low) = 0.01-0.02. As the area of perturbation of the pressure distribution around the rigid sphere is approximately the size range of the rigid sphere, the melt tends to be evenly distributed at a distance from the rigid sphere.