Grain-size reduction mechanisms and rheological consequences in high-temperature gabbro mylonites of Hidaka, Japan
Grain-size reduction mechanisms and rheological consequences in high-temperature gabbro mylonites of Hidaka, Japan
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DOI：
10.1016/j.epsl.2007.12.012
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发表时间：
2008-03
影响因子：
5.3
通讯作者：
H. Raimbourg;T. Toyoshima;Y. Harima;G. Kimura
中科院分区：
文献类型：
--
作者：
H. Raimbourg;T. Toyoshima;Y. Harima;G. Kimura
对日高变质带麻粒岩相剪切带的显微构造和晶体组构的研究表明，糜棱岩内部的强烈剪切作用导致了继承性斜方辉石碎斑岩的不对称拉长，并产生了细晶斜长石层和斜方辉石层，作为斜方辉石碎斑岩的不对称尾部。斜方辉石碎斑岩及其周围的粗斜长岩基质具有通过位错蠕变变形而获得的强结晶学择优取向。与此相反，小斜方辉石和斜长石颗粒位于尾巴有equant形状和随机织物被解释为变形的结果，晶界滑动。小斜方辉石颗粒产生的剪切边缘的斜方辉石碎斑通过亚晶粒旋转，继承的定向变形前的碎斑晶界滑动（GBS），失去了这个面料。粒度减小的另一机制是单斜辉石出溶体上的人工剪切带对斜方辉石碎斑的破坏。从位错蠕变GBS的变形机制的开关，与晶粒尺寸的减小，产生偏应力的估计一个订单小于岩石静压力。此外，这种流变学演化也证明了变形过程中的机械软化作用，从而导致了应变在糜棱岩内部的局部化。
The study of microstructures and crystallographic fabrics in a granulite-facies shear zone of the Hidaka Metamorphic Belt showed that the strong shearing localized within the mylonite resulted in the asymmetrical elongation of the inherited orthopyroxene porphyroclasts and the generation of fine-grained plagioclase and orthopyroxene layers as asymmetric tails of orthopyroxene porphyroclasts. The orthopyroxene porphyroclasts and the coarse plagioclase matrix surrounding them have a strong crystallographic preferred orientation acquired through deformation by dislocation creep. In contrast, the small orthopyroxene and plagioclase grains located in the tails have equant shapes and random fabric that are interpreted as the result of deformation by grain-boundary sliding. The small orthopyroxene grains are generated on the sheared rims of the orthopyroxene porphyroclasts by subgrain rotation, inheriting the orientation of the porphyroclasts before deforming by grain-boundary sliding (GBS) and losing this fabric. Additional mechanism of grain-size reduction is the disruption of orthopyroxene porphyroclasts by synthetic shear zones localized on clinopyroxene exsolutions. The switch in deformation mechanism from dislocation creep to GBS, associated with the grain-size reduction, yielded estimates of deviatoric stress one order smaller than lithostatic pressure. Besides, such rheological evolution attests of the mechanical softening during deformation, which contributed to the localization of the strain within the mylonite.