Subduction and exhumation are key processes in the formation of orogenic systems across the world, for example, in the European Alps. For geophysical investigations of these orogens, it is essential to understand the petrophysical properties of the rocks involved. These are the result of a complex interaction of mineral composition and rock fabric including mineral textures (i.e., crystallographic preferred orientations). In this study we present texture-derived elastic anisotropy data for a representative set of different lithologies involved in the Alpine orogeny. Rock samples were collected in the Lago di Cignana area in Valtournenche, in the Italian northwestern Alps. At this locality a wide range of units of continental and oceanic origin with varying paleogeographic affiliations and tectono-metamorphic histories are accessible. Their mineral textures were determined by time-of-flight neutron diffraction. From these data the elastic properties of the samples were calculated. The data set includes representative lithologies from a subduction-exhumation setting. In subducted lithologies originating from the oceanic crust, the P-wave anisotropies (AVPs [%]) range from 1.4 % to 3.7 % with average P-wave velocities of 7.20–8.24 km/s and VP $/$ VS ratios of 1.70–1.75. In the metasediments of the former accretionary prism the AVPs range from 3.7 % to 7.1 %, average P-wave velocities are 6.66–7.23 km/s and VP $/$ VS ratios are 1.61–1.76. Continental crust which is incorporated in the collisional orogen shows AVP ranging from 1.4 % to 2.1 % with average P-wave velocities of 6.52–6.62 km/s and VP $/$ VS ratios of 1.56–1.60. Our results suggest that mafic and felsic rocks in subduction zones at depth may be discriminated by a combination of seismic signatures: lower anisotropy and higher VP $/$ VS ratio for mafic rocks, and higher anisotropy and lower VP $/$ VS ratio for felsic rocks and metasediments.

中文翻译：

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俯冲和折返环境中岩石的弹性各向异性

俯冲和剥脱是全球造山系统形成的关键过程，例如在欧洲阿尔卑斯山。对于这些造山带的地球物理研究，了解所涉及岩石的岩石物理特性是必不可少的。这些是矿物成分和包括矿物纹理（即晶体优先取向）在内的岩石结构复杂相互作用的结果。在这项研究中，我们提供了高山造山运动中涉及的一组具有代表性的不同岩性的纹理衍生的弹性各向异性数据。岩石样本是在意大利西北部阿尔卑斯山 Valtournenche 的 Lago di Cignana 地区收集的。在这个地方，可以访问范围广泛的大陆和海洋单元，具有不同的古地理隶属关系和构造变质历史。它们的矿物结构是通过飞行时间中子衍射确定的。从这些数据计算样品的弹性性能。该数据集包括来自俯冲-剥脱环境的代表性岩性。在源自洋壳的俯冲岩性中，P 波各向异性 (AVPs [%]) 范围从 1.4% 到 3.7%，平均 P 波速度为 7.20–8.24 km/s 和 VP $/$ VS 比率为 1.70–1.75。在前增生棱柱的变质沉积物中，AVP 范围从 3.7% 到 7.1%，平均 P 波速度为 6.66–7.23 km/s 和 VP $/$ VS 比率为 1.61–1.76。包含在碰撞造山带中的大陆地壳显示 AVP 范围为 1.4% 至 2.1%，平均 P 波速度为 6.52–6.62 km/s 和 VP $/$ VS 比率为 1.56–1.60。我们的研究结果表明，深部俯冲带中的基性岩和长英质岩可以通过地震特征的组合来区分：较低的各向异性和较高的 VP $/$ 基性岩的 VS 比，以及更高的各向异性和更低的 VP $/$ 长英质岩石和变质沉积物的 VS 比率。