Collaborative Research: Examining the Evolution of the Colorado Plateau and Its Relation to the Surrounding Tectonic Provinces Using USArray Data

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)提供资金的。在新生代，北美西南部经历了从法拉隆俯冲到现在太平洋-北美走滑板块边界的转换，即圣安德烈亚斯断裂系统(SAF)。因此，美国西南部的大部分地区经历了伸展，部分原因是从汇聚到当前转换边界的过渡之前和期间造山塌陷的结果。然而，变形和火山活动仍然发生在离板块边界很远的地方，穿过盆地和山脉，围绕科罗拉多高原的边缘，以及落基山脉。大陆岩石圈的结构与每个构造省下的上地幔更深的结构有关，岩石圈和更深的结构的细节以及对构造体制变化的总体响应尚不清楚。随着美国阵列移动阵列在整个大陆上滚动，它统一覆盖了美国西部，记录了远程地震。这些数据，再加上来自LA Ristra、Deep Probe和CD-ROM实验的数据，以及来自亚利桑那州粗略阵列的数据，将提供关于岩石圈和上地幔结构的丰富信息。这些模型将受到以往活动源岩数据的制约。该项目正在研究从地壳到660公里不连续面的三维结构，以系统地寻找重要的构造/地球动力学指标：均衡支撑源、热不平衡区、部分熔融和流变学不均质性、板片碎片和板片与过渡带的相互作用。所生成的图像将用于解释科罗拉多高原与其周围构造省：南部盆地和山脉、南部落基山脉和里奥格兰德裂谷的演化有关的4D构造和地球动力学演化。研究使用面波层析成像和P波和S波接收器功能相结合的方法来清晰地成像地壳底部、岩石圈-软流圈边界(LAB)、并通过美国西南部四角地区下方过渡带的上地幔结构，结合以往的宽带阵列研究，得到了共转换点(CCP)叠加的PDS和SDP接收器功能和面波层析成像成像体。利用两种类型的散射波构造了接收函数：P转换为S(PDS)，S转换为P(SDP)。PDS和SDP的使用允许同一地区的独立模型，并提供不同的调查频段和不同的射线路径来成像岩石圈和上地幔结构。由于接收函数和面波频散对速度结构具有不同的敏感性，联合反演接收函数和剪切速度值可提供对结构的独立估计。接收函数成像速度-密度不连续，而不是绝对速度结构。它能感觉到高频的速度波动，在某些情况下，密度在垂直方向上也会波动。面波的相速度对绝对剪切速度结构最为敏感。原则上，两者可以联合反演，以克服接收函数反演的非唯一性和面波层析成像较低的垂直分辨率。用多种方法绘制莫霍面、实验室和过渡带不连续面的三维变化，将为解释美国西南部下的4D新生代伸展、挤压和局部对流特征(上升流、减压熔融和地幔滴滴)提供一致的框架。本研究结果将对美国西部和其他地区对大陆演化、伸展动力学、地球动力学、火山学和构造地质学感兴趣的非地震学家有用。该方法将适用于其他区域阵列数据，包括未来的美国阵列数据。两名研究生将接受使用地震阵列数据和综合地球物理解释的培训。除了该项目的研究目标外，该奖项还将支持南加州大学的一名新研究员以及两名研究生的教育和培训。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). During the Cenozoic, southwestern North America underwent a shift from Farallon subduction to the present Pacific - North American strike-slip plate boundary, the San Andreas fault system (SAF). As a result, much of the southwestern U.S. experienced extension, in part the result of orogenic collapse prior to and during the transition from convergence to the current transform boundary. Yet deformation and volcanism still occur at great distances from the plate boundary, through the Basin and Range, around the edges of the Colorado Plateau, and in the Rocky Mountains. The structure of the continental lithosphere is linked to structures deeper in the upper mantle beneath each of tectonic provinces, and the details of the lithosphere and deeper structure and the overall response to the change in tectonic regime are not clearly understood. As the USArray Transportable Array rolls across the continent, it is uniformly covering the Western U.S., recording teleseismic earthquakes. These data, plus data integrated from the LA RISTRA, Deep Probe, and CD-ROM experiments in addition to data from the COARSE array in Arizona, will provide a wealth of information on the lithosphere and upper mantle structure. These models will be constrained by previous active source and petrologic data. This project is examining, in 3D, the Earth's discontinuity structure from the crust thru the 660 km discontinuity to systematically look for important tectonic/geodynamic indicators: sources of isostatic support, regions of thermal disequilibrium, partial melt, and rheological heterogeneity, slab fragments and slab interactions with the transition zone. The resulting images will be used to interpret the 4D tectonic and geodynamic evolution of the Colorado Plateau in relation to the evolution of its surrounding tectonic provinces: southern Basin and Range, southern Rocky Mountains, and the Rio Grande Rift.The research uses a combination of surface wave tomography and P- and S-wave receiver functions to clearly image the base of the crust, the lithosphere-asthenosphere boundary (LAB), and the upper mantle structure through the transition zone beneath the Four Corners area of the southwestern U.S. USArray Transportable Array teleseismic data combined with previous broadband array studies have been used to make common conversion point (CCP) stacked PdS and SdP receiver function and surface wave tomography image volumes. The receiver functions have been made with two types of scattered waves: P converted to S (PdS), and S converted to P (SdP). The use of both PdS and SdP allows for independent models of the same area, and provides different frequency bands of investigation and different raypaths to image lithospheric and upper mantle structure. Since receiver functions and surface wave dispersion have different sensitivities to velocity structure jointly inverting the receiver functions and the shear velocity values provides independent estimates of structure. A receiver function images velocity-density discontinuities, not the absolute velocity structure. It senses the high frequency velocity fluctuations, and in some cases density fluctuations in the vertical direction. Phase velocities of surface waves, on the other hand, are most sensitive to the absolute shear velocity structure. In principle the two can be inverted jointly to overcome the non-uniqueness of the receiver-function inversion and the lower vertical resolution of surface-wave tomography.Mapping 3D variations in the Moho, the LAB, and the transition zone discontinuities with multiple methods will provide a consistent framework for interpreting 4D Cenozoic extension, compression, and local convection features (upwellings, decompression melts, and mantle drips) beneath the southwestern U.S. Results of this study will be useful to non-seismologists interested in continental evolution, extensional dynamics, geodynamics, volcanology, and structural geology, both in the western U.S. and elsewhere. The methodology will be applicable to other regional array data, including future USArray data. Two graduate students will be trained in the use of seismic array data and integrated geophysical interpretation.In addition to the research objectives of this project, the award will support a new investigator at the University of Southern California and the education and training of two graduate students.