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迄今为止,上地幔流变学的研究主要集中于橄榄石单晶与多晶集合体的实验和野外观察,但对辉石的流变学特征知之甚少,虽然辉石亦是上地幔岩石的主要组成矿物。因此,查清斜方辉石的流变学行为、塑性变形机制、重结晶作用以及与其共生的橄榄石之间的流变强度差等,现已成为国际地学界研究的新的热点课题。新疆中天山南缘库米什地区的榆树沟高压变质地体中出现地幔超糜棱岩,其中带状拉伸的斜方辉石(En90)碎斑晶发生了强烈地弯滑褶皱,周围橄榄石(Fo90)重结晶成细粒(~10μm)多晶基质。显微构造研究表明,单晶斜方辉石的褶皱主要通过单一的(100)[001]滑移进行的,而细粒重结晶橄榄石基质的变形机制则最可能以超塑性(颗粒边界滑移与扩散)为主。单晶斜方辉石发生弯滑褶皱,而不形成常见的膝折(Kinks),说明所处物理化学条件下斜方辉石晶体位错攀移与原子扩散并不足够活跃。此外,即使其晶格发生高达140°的旋转,斜方辉石依然没有发生光学显微镜下足以识别的重结晶结构,说明启动重结晶作用的临界剪切应变应不少于5.5。根据现有的层状材料的褶皱理论,推测榆树沟高压变质地体中地幔岩发生塑性变形时位错蠕变的斜方辉石的流动强度至少比相同条件下超塑性变形的细粒橄榄石多晶基质高近2个数量级。
So far, the study of rheology in the upper mantle has mainly focused on the experimental and field observations of olivine single crystals and polycrystalline aggregates, but little is known about the rheological characteristics of pyroxenes, although pyroxenes are also upper mantle rocks Mainly composed of minerals. Therefore, it has become a new hot topic in the field of international geosciences to find out the rheological behavior, plastic deformation mechanism, recrystallization and poor rheological strength between orthopyroxene and olivine. In the Yushugou high-pressure metamorphic terrane of the Kumish region on the southern margin of the middle Tianshan Mountains, there is an over-mylonite mantle, in which strip-shaped En90 porphyritic crystals are strongly bent and folds, Stone (Fo90) was recrystallized to a fine (~ 10 μm) polycrystalline matrix. Microstructural studies have shown that the fold of orthorhombic single crystal mainly through a single (100) [001] slip, while the deformation mechanism of fine recrystallized olivine matrix is most likely to superplastic (grain boundary slip Shift and proliferation) based. The orthorhombic clinopyroxenes show kinks and folds without forming common kinks (Kinks), indicating that the dislocation climbing and atomic diffusion of orthopyroxene crystals are not active enough under the physicochemical conditions. In addition, orthopyroxene did not undergo recalciton microscopy to identify recrystallized structures even though their lattice rotated up to 140 °, indicating that the critical shear strain at which recrystallization should be initiated should not be less than 5.5. According to the existing fold theory of layered materials, it is speculated that the flow strength of orthopyroxene during the plastic deformation of the mantle rock in the Yushugou high-pressure metamorphic body is at least as good as the superplastic deformation of the fine-grained olivine under the same conditions Polycrystalline matrix nearly 2 orders of magnitude higher.