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Surface velocities in parts of the India–Asia collision zone are compared to velocities calculated from equations describing fluid flow driven by topographically produced pressure gradients. A good agreement is found if the viscosity of the crust is ∼1020 Pa s in southern Tibet and ∼1022 Pa s in the area between the Eastern Syntaxis and the Szechwan Basin. The lower boundary condition of the flow changes between these two areas, with a stress-free lower boundary in the area between the Szechwan basin and the Eastern Syntaxis, and a horizontally rigid but vertically deformable boundary where strong Indian lithospheric material underlies southern Tibet. Deformation maps for olivine, diopside and anorthite show our findings to be consistent with laboratory measurements of the rheology of minerals. Gravitationally driven flow is also suggested to be taking place in the Indo–Burman Ranges, with a viscosity of ∼1019 –1020 Pa s. Flow in both southern Tibet and the Indo–Burman Ranges provides an explanation for the formation of the geometry of the Eastern Himalayan Syntaxis. The majority of the normal faulting earthquakes in the Tibetan Plateau occur in the area of southern Tibet which we model as gravitationally spreading over the Indian shield. 相似文献
134.
Okada (1992) provided expressions for the displacement and strain fields due to a finite rectangular source in an elastic, homogeneous and isotropic half-space. Starting with these results, we applied the correspondence principle of linear viscoelasticity to derive the quasi-static displacement, strain and stress fields in a viscoelastic, homogeneous and isotropic half-space. We assume that the medium deforms viscoelastically with respect to both the shear and the normal stresses but keeps a constant bulk modulus; in particular, the shear modulus relaxes as Maxwell fluid. We presented the viscoelastic effect on displacement, displacement gradient and stress fields, for a choice of parameter values. The viscoelastic effect due to the sudden dislocation reaches a limit value after about 10 times the Maxwell time. The expressions obtained here provide tools for the study of viscoelastic relaxation of lithosphere associated with seismic and volcanic phenomena. 相似文献
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Deformation-enhanced metamorphic reactions and the rheology of high-pressure shear zones, Western Gneiss Region, Norway 总被引:4,自引:1,他引:4
Microstructural and petrological analysis of samples with increasing strain in high‐pressure (HP) shear zones from the Haram garnet corona gabbro give insights into the deformation mechanisms of minerals, rheological properties of the shear zone and the role of deformation in enhancing metamorphic reactions. Scanning electron microscopy with electron backscattering diffraction (SEM–EBSD), compositional mapping and petrographic analysis were used to evaluate the nature of deformation in both reactants and products associated with eclogitization. Plagioclase with a shape‐preferred orientation that occurs in the interior part of layers in the mylonitic sample deformed by intracrystalline glide on the (0 0 1)[1 0 0] slip system. In omphacite, crystallographic preferred orientations indicate slip on (1 0 0)[0 0 1] and (1 1 0)[0 0 1] during deformation. Fine‐grained garnet deformed by diffusion creep and grain‐boundary sliding. Ilmenite deformed by dislocation glide on the basal and, at higher strains, prism planes in the a direction. Relationships among the minerals present and petrological analysis indicate that deformation and metamorphism in the shear zones began at 500–650 °C and 0.5–1.4 GPa and continued during prograde metamorphism to ultra‐high‐pressure (UHP) conditions. Both products and reactants show evidence of syn‐ and post‐kinematic growth indicating that prograde reactions continued after strain was partitioned away. The restriction of post‐kinematic growth to narrow regions at the interface of garnet and plagioclase and preservation of earlier syn‐kinematic microstructures in older parts layers that were involved in reactions during deformation show that diffusion distances were significantly shortened when strain was partitioned away, demonstrating that deformation played an important role in enhancing metamorphic reactions. Two important consequences of deformation observed in these shear zones are: (i) the homogenization of chemical composition gradients occurred by mixing and grain‐boundary migration and (ii) composition changes in zoned metamorphic garnet by lengthening diffusion distances. The application of experimental flow laws to the main phases present in nearly monomineralic layers yield upper limits for stresses of 100–150 MPa and lower limits for strain rates of 10?12 to 10?13 s?1 as deformation conditions for the shear zones in the Haram gabbro that were produced during subduction of the Baltica craton and resulted in the production of HP and UHP metamorphic rocks. 相似文献
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Vladimir Lyakhovsky Yehuda Ben-Zion Amotz Agnon 《Geophysical Journal International》2005,161(1):179-190
139.
超高压变质岩的塑性流变学 总被引:1,自引:1,他引:0
岩石流变作用是大陆造山作用的基本特征,超高压岩石的形成和折返过程也是大陆深俯冲带内物质的复杂流变过程。要深入理解大陆造山带的造山作用和大陆壳岩石的深俯冲和折返动力学过程,必须对大陆地壳及地幔岩石的流变学进行深入研究。岩石圈流变学的主要研究内容主要包括流变学分层性、变形分解和应变局部化及大陆壳岩石部分熔融作用的流变学效应等。应用岩石圈流变学的基本原理和方法,分析了大别-苏鲁超高压变质带中超高压变质岩的塑性流变特点,探讨了超高压变质岩形成和折返过程的塑性流变学。 相似文献
140.
共轭剪切角的流变学意义 总被引:1,自引:1,他引:0
基于最大侧向位移速率假设(Maximum lateral displacement rate, 简称MLDR), 本文提出了一个关于共轭剪切角的流变学理论。根据这个假设, 无论是压应力或张应力作用在一个固体上, 剪切带总是沿着使得被剪切带分割的块体的侧向位移速率为最大的方向发育。换句话说, 如果平行于驱动应力的纵向位移速率或驱动应力的大小被看作为边界条件, 那些被剪开的块体总是以最快的可能速度从两侧挤出或饲入变形区。该理论的优点是:剪切位移的方向是可逆的。因此, 同一剪切带可以在挤压和拉张应力体系中活动。在各向同性固体中, 剪切带的方位和驱动应力方向之间的夹角θ由方程式 tan θ= 确定, 其中n为描述该固体塑性流动的幂指数。 相似文献