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

内华达州红宝石山脉核心复合体延伸区的 Flexarray 3D 被动地震成像

• 批准号: 0844386
• 负责人: Simon Klemperer
• 金额: $ 13.62万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-06-01 至 2014-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0844386&HistoricalAwards=false
• 关键词: Flexarray; 3D; Passive; Seismic; Imaging

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).

大陆地壳伸展程度最高的区域被称为核杂岩，它们的边界结构通常被标为低角度断层，尽管这些与地壳力学行为的预测背道而驰，但它们属于大陆伸展最具争议的方面。这些特征很难解释，因为科学家们缺乏关于它们深厚基础的清晰图像。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，从而能够对地壳中的二维横截面进行成像。EarthScope的FlexArray最终提供了足够的仪器，可以在地表部署二维阵列，从而可以重建深度的三维(3D)图像体积。内华达州的盆山省提供了无与伦比的各种伸展风格的暴露，包括变质核杂岩，它们将韧性变形的中地壳岩石与未变质、脆性变形的表壳岩石并列在一起。这种关系意味着显著的水平伸展，在整个地壳的尺度上被大规模的简单剪切或下部地壳的显著横向和垂直流动所补偿。要弄清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，才能令人信服地表明地表地质是如何与深部地貌相联系或脱节的。在伸展省份的构造重建中，所涉及的总伸展的不确定性是一个主要的未知因素，而世界各地都有这样的核心杂岩。美国国家科学基金会？S地球镜科学计划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(拉莫耶-亨廷顿山谷和红宝石山谷)进行3D研究，以寻找地壳流入变质核的证据。这一地区之所以成为目标，是因为鲁比山周围的现有数据可以在更大的3D体积中对新的地球物理结果进行详细解释。利用40台无源宽带地震仪阵列对地壳和上地幔进行详细的FlexArray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、变形和演化以及伸展造山带所涉及的岩石圈尺度过程的了解。已建立的被动记录技术(环境噪声层析成像、接收函数速度反演、共转换点成像、地壳各向异性分析)正在以3D形式应用，而不是更常见的二维，且分辨率(间隔5公里)高于此类研究的典型分辨率。这一实验结果将使对延伸区下方深部地壳流动模型的评估成为可能，从而有助于理解跨延伸区的低地壳应变在空间和时间上的进展。更详细地描述这些过程是推进我们对大陆裂谷作用和世界范围内沉积盆地演化的认识的根本步骤。活跃在内华达州的金矿公司也应该对这一结果感兴趣：红宝石山脉可能揭示邻近的卡林趋势的基础，这是美洲最大的黄金产区，并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。