Reconstruction of the continental lower-crust rheology based on the rheology data of plagioclase

本文对北海道日高变质带的辉长岩（a）和角闪岩（B）、意大利西北部伊夫雷亚带的角闪岩（c）和花岗闪长岩（d）、阿曼蛇绿岩中的角闪岩（e）和巴基斯坦北部科希斯坦弧中的角闪岩（f）中的糜棱岩样品进行了显微结构观察和晶体学取向测量。矿物组合和测温结果表明，（a）变形于麻粒岩-角闪岩相转变（660-700℃），（B）-（f）变形于角闪岩相（520-650℃），斜长石在此变形条件下发生了晶界迁移的动态重结晶。在角闪岩相变形的斜长石碎斑岩中没有发现亚晶界等恢复的证据，而在麻粒岩-角闪岩相转变变形的斜长石碎斑岩中发现了亚晶界等恢复的证据 ...更多信息 显示出晶体学择优取向（CPO）与{121}和<111>次平行面理和线理，分别，但它的关系，占主导地位的滑移系统仍然未知。相反，麻粒岩-角闪岩相转变处的颗粒表现出的CPO<110>分别与面理和线理（001）和近平行。由于斜长石中的（001）1/2<110>滑移系是已知的，该滑移系可能在斜长石中占主导地位，从而揭示了斜长石在角闪岩相到麻粒岩-角闪岩相转变条件下变形的动态重结晶机制、回复程度、CPO的发展及其随变形温度的变化，是对现有斜长石流变学资料的重要补充。然而，由于没有获得斜岩在超高压相的变形数据，以及没有建立气体介质三轴实验装置，无法进行高温高压下的斜岩变形实验，我们无法重建大陆下地壳的流变学。少

We have made microstructural observations and crystallographic-orientation measurements of crystal-plastically deformed plagioclase grains in mylonite samples derived from gabbro (a) and amphibolite (b) in the Hidaka metamorphic belt of Hokkaido, amphibolite (c) and granodiorite (d) in the Ivrea Zone of NW Italy, amphibolite (e) in the Oman ophiolite, and amphibolite (f) in the Kohistan Arc of N Pakistan. Mineral assemblages and geothermometric applications indicate deformation of (a) at the granulite-amphibolite facies transition (660-700℃), while deformations of (b)-(f) at amphibolite facies (520-650℃).Dynamic recrystallization of plagioclase occurred by grain boundary migration at these deformation conditions. Evidence for recovery such as subgrain boundaries was not found in plagioclase porphyroclasts deformed at amphibolite facies, but found in those deformed at the granulite-amphibolite facies transition.Plagioclase grains dynamically recrystallized at amphibolite facies commonly … More exhibit a crystallographic preferred orientation (CPO) with {121} and <111> subparallel to foliation and lineation, respectively, but its relation to the dominant slip system remains unknown. In contrast, those grains at the granulite-amphibolite facies transition exhibit a CPO with (001) and <110> subparallel to foliation and lineation, respectively. Because (001) 1/2 <110> is known as a slip system in plagioclase, this slip system was likely dominant in these grains.Thus the dynamic recrystallization mechanism, extent of recovery, CPO developed, and their changes with deformation temperature were revealed for plagioclase deformed at the conditions from amphibolite facies to the granulite-amphibolite facies transition, which are an important addition to the existing data on the rheology of plagioclase. However, we could not reconstruct the rheology of the continental lower crust, because we could not obtain data on plagioclase deformed at granulate facies, and also because we could not conduct deformation experiments on plagioclase at high pressures and temperatures due to a gas-medium triaxial apparatus being not set up yet. Less