Flexarray 3D Passive Seismic Imaging of Core-complex Extension in the Ruby Range, Nevada

大陆地壳最高度伸展的区域，被称为核杂岩，以及它们的边界结构，通常被绘制成低角度断层，尽管这些构造与地壳力学行为的预测不符，是大陆伸展最有争议的方面之一。 这些特征难以解释，因为科学家们缺乏对其深层基础的清晰图像。Earthscope的FlexArray允许新一代成像程序。 传统上，研究岩石圈的地震学家受到现有设备的限制，只能部署单线接收器，从而无法对地壳的二维横截面进行成像。Earthscope的FlexArray最终提供了足够的仪器，可以在表面部署二维阵列，从而可以在深度重建三维（3D）图像体积。 内华达州的盆岭省提供了无与伦比的多种伸展方式的暴露，包括变质核杂岩，它将韧性变形的中地壳岩石与未变质的脆性变形的表壳岩并列。这种关系意味着显著的水平伸展，在整个地壳的规模上被大规模的简单剪切或下地壳的显著的横向和垂直流动所补偿。要阐明上地壳和下地壳同时变形之间的关系，需要有足够分辨率的地球物理数据，以令人信服地显示地表地质如何与深部特征相联系或相分离。总拉伸的不确定性是一个主要的未知在构造重建的伸展区，无论这样的核心复杂发生在世界各地。国家科学基金会？的地球镜科学计划正在与美国化学学会石油研究基金合作，赞助对经典的红宝石山变质核杂岩及其邻近盆地（Lamoille-Huntington Valley红宝石谷）进行3D研究，以寻找地壳流入变质核的证据。 之所以选择这一地区，是因为围绕红宝石山脉的现有数据允许在更大的3D体积中详细解释新的地球物理结果。FlexArray利用40个测站的被动宽带地震仪阵列对地壳和上地幔进行详细的地球物理研究，将在可移动阵列数据和地表地质数据之间提供重要的联系，以加深对大陆结构、变形和演变以及伸展造山带所涉及的岩石圈规模过程的了解。已建立的被动记录技术（环境噪声层析成像、接收器功能速度反演、共转换点成像、地壳各向异性分析）正在以3D而不是更常见的二维和更高的分辨率应用（5公里的间距）比这类研究的典型。这一实验的结果将允许评估模型的地壳流动在深度以下延伸的地区，从而有助于了解下地壳应变在空间和时间上跨越延伸区域的进展。更详细地描述这些过程是推进我们对大陆裂谷和全球沉积盆地演化的认识的基本步骤。 这些结果也会引起活跃在内华达州的金矿公司的兴趣：红宝石山脉可能会暴露出邻近的卡林趋势的基础，卡林趋势是美洲最大的黄金生产区，同时有助于了解导致内华达州50多年来最具破坏性的地震（2008年2月威尔斯6级地震）的地质框架。

The most highly-extended regions of continental crust, known as core-complexes, and their bounding structures, typically mapped as low-angle faults even though these defy predictions of the mechanical behavior of the crust, are among the most controversial aspects of continental extension. These features have defied easy explanation because scientists have lacked clear images of their deep underpinnings. Earthscope's FlexArray is allowing a new generation of imaging procedures. Traditionally, seismologists studying the lithosphere have been restricted by limitations on available equipment to deploying single lines of receivers, allowing imaging of two-dimensional cross-sections through the crust. Earthscope's FlexArray finally provides enough instrumentation that a two-dimensional array at the surface can be deployed, allowing reconstruction of a three-dimensional (3D) image volume at depth. The Basin-and-Range Province in Nevada offers unparalleled exposure of diverse styles of extension, including the metamorphic core complexes that juxtapose ductilely deformed mid-crustal rocks with unmetamorphosed, brittly-deformed supracrustal rocks. This relationship implies significant horizontal extension, compensated at the scale of the whole crust either by large-magnitude simple shear or significant lateral and vertical flow of the lower crust. Elucidating the relationship between simultaneous deformation of the upper and lower crust requires geophysical data of sufficient resolution to convincingly show how the surface geology is linked to - or disconnected from - features at depth. Uncertainty in the total stretching involved is a major unknown in tectonic reconstruction of extensional provinces wherever such core complexes occur around the world. The National Science Foundation?s Earthscope Science program is teaming with the Petroleum Research Fund of the American Chemical Society to sponsor a 3D study of the classic Ruby Mountain Metamorphic Core Complex and its adjacent basins (Lamoille-Huntington Valley & Ruby Valley) to look for evidence of crustal flow into the metamorphic core. This region is being targeted because the existing data that surround the Ruby Mountains allow detailed interpretation of the new geophysical results in a larger 3D volume. The detailed FlexArray geophysical studies of the crust and upper mantle, using a 40-station array of passive, broadband seismometers, will provide an important link between Transportable Array data and surface geologic data to develop understanding of continental structure, deformation and evolution, and the lithospheric-scale processes involved in extensional orogens. Established passive-recording techniques (ambient-noise tomography, receiver-function velocity inversions, common-conversion point imaging, crustal anisotropy analyses) are being applied in 3D instead of the more commonplace two dimensions, and at a higher resolution (5-km spacing) than is yet typical for this class of studies.Results of this experiment will allow evaluation of models for crustal flow at depth beneath extending regions, and thereby help understand the progression of lower-crustal strain in space and time across extending regions. Characterizing these processes in more detail is a fundamental step towards advancing our knowledge of continental rifting and the evolution of sedimentary basins world-wide. The results should also be of interest to gold-mining companies active in Nevada: the Ruby Range may expose underpinnings of the adjacent Carlin Trend, the largest gold-producing region in the Americas, as well as helping understand the geologic framework that gave rise to Nevada's most destructive earthquake for over 50 years (the February 2008 Wells magnitude 6 earthquake).