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

来自犹他州大学的Phil Wannamaker正在制作和解释大盆地中部和西部以及东南部莫多克高原的高质量电阻率结构剖面图。这是通过在现有的179个样带上增加55个宽带大地电磁测深，加上安装35个长周期大地电磁测深，以建立一个横跨内华达州和加州东北部到最西端犹他州的长约650公里的样带来实现的。大地电磁台站的数据将跨越0.005到10，000秒波周期的范围，相应的成像深度从几百米到大约300公里，甚至更大。剖面覆盖了莫多克高原的全部100公里，该高原是活跃延伸的西北大盆地、中部内华达州地震带、相对静止的中东部高海拔大盆地，并与犹他州西部活跃的东部大盆地重叠。这些数据正在经历现代处理方法，趋势分析和正则化反演，以产生具有最小伪影的高分辨率模型。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认识。裂谷作用的后果可能是深远的，包括可能发生大地震、沉积盆地的发展以及最终大陆分裂形成新的海洋盆地。许多重要的碳氢化合物、地热和矿物资源的出现可能来自伸展所涉及的构造、岩浆和热液过程。该项目特别是解决一级问题的垂直应变分布，岩浆地壳生长，地壳尺度流体流动的域，岩石圈和软流圈之间的耦合仍然没有解决。这些问题包括：地壳尺度断裂带的普遍性，这些断裂带承载着最大的地震;在什么情况下，上地壳和下地壳减薄是分离的;在裂谷过程中，地幔岩石圈是弱还是强;在大陆裂谷的早期到中期阶段，是否发生体积上显著的岩浆输入;以及幔源流体如何进入浅层地下水系统。该项目还涉及社会效益，包括更广泛地了解断层强度，地壳尺度水文学和建立破坏性应力的能力。深部地热系统和浅成热液金矿之间的联系也得到了阐明。正在支持一名研究生接受教育，学习最先进的地球物理仪器、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中电阻率与物理化学状态之间的关系。相关的配套项目有可能提供接近区域到国家尺度的第一批结果，公众的兴趣是通过从加州太平洋海岸附近到犹他州的科罗拉多高原内部的潜在大断面提供的不同区域的截面视图来预期的。东部边境。除了研究之外，该项目还支持一名博士的研究生培训。来自地球科学中一个代表性不足的群体的学生，研究大地电磁法。该研究的资金由NSF地球物理和构造计划提供。

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.