Modes of Extension, Magmatism and Crustal Scale Fluid Pathways in the Great Basin province, USA, from a Magnetotelluric Transect

来自犹他大学的Phil Wannamaker正在制作并解释大盆地中部和西部以及莫多克高原东南部的高质量电阻率结构剖面图。这是通过在现有的179个地点的样带上增加55个宽带大地电磁测深，再加上安装35个长周期大地电磁测深来实现的，这样就形成了一个长约650公里的样带，横跨内华达州和加利福尼亚州东北部，一直到犹他州最西部。大地电磁测量站的数据将跨越0.005至10,000次第二波周期，相应的成像深度从几百米到大约300公里，甚至更大。该剖面覆盖了莫多克高原、活跃伸展的西北大盆地、内华达中部地震带、相对静止的高海拔东中部大盆地，并覆盖了活跃的犹他州西部东部大盆地，全长100公里。这些数据正在经历现代方法的处理、趋势分析和正则化反演，以产生一个具有最小人为因素的分辨率良好的模型。该项目的总体目标是提高我们对分布式大陆裂谷作用过程的理解。裂谷作用的后果可能是深远的，包括可能发生大地震，形成沉积盆地，并最终导致大陆分裂，形成新的海洋盆地。许多重要的碳氢化合物、地热和矿产资源的赋存可能产生于伸展过程中涉及的构造、岩浆和热液作用。该项目具体解决了垂直应变分布、岩浆地壳生长、地壳尺度流体流动域以及岩石圈和软流圈耦合等一级问题尚未解决。其中包括地壳规模断层带的普遍存在，这些断层带承载着最大的地震；在什么情况下，上地壳和下地壳的薄化是分离的；裂谷期地幔岩石圈弱或强；在大陆裂陷的早期到中期是否存在具有体积意义的岩浆输入；以及地幔源流体是如何进入浅层地下水的。该项目还涉及社会效益，包括更广泛地了解断层强度控制、地壳尺度水文以及建立破坏性应力的能力。深层地热系统与浅成热液型金矿床之间的联系也得到了阐明。支持一名研究生学习最新的地球物理仪器、野外调查设计参数、偏远地区的实际后勤问题、现代反演方法以及地球电阻率与物理化学状态之间的关系。相关的伙伴项目有可能提供第一个接近区域到国家尺度的结果，公众对从加利福尼亚太平洋海岸附近到犹他州科罗拉多高原内部的潜在巨型横贯所提供的不同区域的剖面图感兴趣。美国东部边境。除了研究之外，该项目还支持一名来自地球科学中代表性不足的群体的博士生在大地电磁方法方面的研究生培训。这项研究的资金由美国国家科学基金会地球物理学和构造学项目提供。

Phil Wannamaker from the University of Utah is producing and interpreting a high-quality section view of electrical resistivity structure through the central and western Great Basin, and the southeastern Modoc Plateau. This is being achieved by the addition of 55 wideband magnetotelluric soundings to an existing transect of 179 sites, plus installation of 35 long-period magnetotelluric soundings, to create a transect some 650 km in length span-ning Nevada and northeastern California into westernmost Utah. The magnetotelluric station data will span the range of 0.005 to 10,000 second wave periods, with corresponding imag-ing depths from a few hundred meters to about 300 km, and perhaps greater. The profiling covers fully 100 kilometers of the Modoc Plateau, the actively extending northwestern Great Basin, the Central Nevada Seismic Belt, the relatively quiescent east-central Great Basin of higher elevation, and onlaps the active eastern Great Basin of western Utah. These data are undergoing modern methods of processing, trend analysis, and regularized inversion to pro-duce a well-resolved model with minimal artifacts. The overall goal of the project is to im-prove our understanding of the process of distributed continental rifting. The consequences of rifting can be profound, including the potential for large earthquakes, development of sedimentary basins and, ultimately, breakup of continents to form new ocean basins. Many important hydrocarbon, geothermal and mineral resource occurrences can arise from the structural, magmatic and hydrothermal processes involved in extension. The project specifi-cally is addressing first-order problems regarding vertical strain distribution, magmatic crustal growth, domains of crustal scale fluid flow, and coupling between the lithosphere and asthenosphere remain unsolved. These include the prevalence of crustal scale fault zones which host the largest earthquakes; under what circumstances upper and lower-crustal thin-ning are decoupled; where mantle lithosphere is weak or strong during rifting; whether volumetrically significant magmatic input occurs during the early to middle stages of conti-nental rifting; and how mantle-sourced fluids make their way to the shallow ground water regime. The project also addresses societal benefits including broader understanding of the controls on fault strength, crustal scale hydrology, and the ability to build up damaging stresses. The link between deep geothermal systems and epithermal gold deposits is being illuminated as well. A graduate student is being supported for education into state of the art geophysical instrumentation, parameters of field survey design, practical logistical matters in remote settings, modern methods of inversion, and the relationship between electrical resis-tivity and physico-chemical state in the Earth. Linked companion projects have the potential to provide the first results approaching regional to national scales, and public interest is ex-pected in section views through diverse regions provided by a potential megatransect from near the California Pacific coast to the Colorado Plateau interior at Utah?s eastern border. In addition to the research, the project is supporting the graduate training of a Ph.D. student from an underrepresented group in the earth sciences in magnetotelluric methods. Funding for the research is being provided by the NSF Geophysics and Tectonics programs.