Abstract We have studied the microstructure, texture and seismic anisotropy of a foliated blueschist-eclogite rock in the Naga Hills Ophiolite (NHO) complex, North-East India. The rock is composed essentially of omphacite, sodic amphibole (glaucophane), sodic-calcic amphibole (barroisite), phengite, and garnet, and represents oceanic crust that experienced Neo-Tethyan subduction and metamorphism before it resurfaced and accreted in the ophiolite. Omphacite and glaucophane show weak shape preferred orientation (SPO), while phengite displays a strong SPO. The Crystallographic Preferred Orientation (CPO) of omphacite is characterized by the [001]-axes gridle within the foliation, and the (010)-poles concentrated sub-perpendicular to the foliation. For glaucophane, the [001] axis aligns parallel to lineation and the [100] axis and (110) pole plunge perpendicular to foliation. These CPOs correspond to SL-type fabrics, related to plane strain deformation geometry. Based on our analysis, we propose that the observed texture had developed from plastic deformation through dislocation creep. Employing the textural data, we have presented the seismic anisotropies of the individual minerals, blueschist-eclogite domains and discussed their contributions in the bulk-rock anisotropy. The calculated bulk-rock seismic anisotropies, AVP and AVS, of the rock are 12.8% and 8.1%, respectively, which correlate with the observed seismic anisotropy of the subducting oceanic crust.

中文翻译：

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印度东北部 Naga Hills 蛇绿岩中深埋洋壳的表面重修：石油结构、微观结构和地震特性

摘要 我们研究了印度东北部 Naga Hills 蛇绿岩 (NHO) 复合体中叶状蓝片岩-榴辉岩的微观结构、质地和地震各向异性。该岩石主要由绿辉石、钠闪石（蓝闪石）、钠钙闪石（重晶石）、菱镁矿和石榴石组成，代表了经历了新特提斯俯冲和变质作用的大洋地壳，然后重新浮出水面并在蛇绿岩中增生。绿辉石和蓝闪石显示出弱的形状择优取向 (SPO)，而菱镁矿显示出强的 SPO。绿辉石的晶体优选取向 (CPO) 的特征在于叶理内的 [001] 轴网格，并且 (010) 极集中在与叶理亚垂直。对于绿光灯，[001] 轴平行于划线排列，而 [100] 轴和 (110) 极点垂直于叶理排列。这些 CPO 对应于与平面应变变形几何相关的 SL 型织物。根据我们的分析，我们提出观察到的纹理是从塑性变形到位错蠕变发展而来的。利用结构数据，我们展示了单个矿物、蓝片岩-榴辉岩域的地震各向异性，并讨论了它们对大块岩石各向异性的贡献。计算出的岩石的大块岩石地震各向异性 AVP 和 AVS 分别为 12.8% 和 8.1%，这与俯冲洋壳的观测地震各向异性相关。我们认为观察到的纹理是从塑性变形到位错蠕变发展而来的。利用结构数据，我们展示了单个矿物、蓝片岩-榴辉岩域的地震各向异性，并讨论了它们对大块岩石各向异性的贡献。计算出的岩石的大块岩石地震各向异性 AVP 和 AVS 分别为 12.8% 和 8.1%，这与俯冲洋壳的观测地震各向异性相关。我们认为观察到的纹理是从塑性变形到位错蠕变发展而来的。利用结构数据，我们展示了单个矿物、蓝片岩-榴辉岩域的地震各向异性，并讨论了它们对大块岩石各向异性的贡献。计算出的岩石的大块岩石地震各向异性 AVP 和 AVS 分别为 12.8% 和 8.1%，这与俯冲洋壳的观测地震各向异性相关。