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

美国大盆地省的伸展模式、岩浆作用和地壳流体通道（来自大地电磁断面）

• 批准号: 0838043
• 负责人: Philip Wannamaker
• 金额: $ 38.26万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838043&HistoricalAwards=false
• 关键词: Modes; Extension; Magmatism; Crustal; Scale

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.

犹他大学的 Phil Wannamaker 正在制作和解释大盆地中部和西部以及莫多克高原东南部的电阻率结构的高质量剖面图。这是通过在现有的 179 个地点的横断面中增加 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，创建一条长约 650 公里的横断面，横跨内华达州和加利福尼亚州东北部，直至犹他州最西部。大地电磁站数据将跨越0.005至10,000秒波周期的范围，相应的成像深度从几百米到约300公里，甚至可能更大。该剖面覆盖了莫多克高原整整 100 公里、活跃延伸的西北大盆地、内华达中部地震带、相对静止的海拔较高的中东部大盆地，并覆盖了犹他州西部活跃的东部大盆地。这些数据正在接受现代方法的处理、趋势分析和正则化反演，以产生具有最少伪影的良好解析模型。该项目的总体目标是提高我们对分布式大陆裂谷过程的理解。裂谷的后果可能是深远的，包括可能发生大地震、沉积盆地的发育，以及最终大陆破裂形成新的海洋盆地。许多重要的碳氢化合物、地热和矿产资源的出现可能是由扩张过程中涉及的构造、岩浆和热液过程产生的。该项目具体正在解决有关垂直应变分布、岩浆地壳生长、地壳尺度流体流动领域以及岩石圈与软流圈之间的耦合等尚未解决的一阶问题。其中包括发生最大地震的地壳规模断层带的普遍存在；在什么情况下上地壳减薄和下地壳减薄是脱钩的？裂谷期间地幔岩石圈弱或强；体积显着的岩浆输入是否发生在大陆裂谷的早期到中期；以及源自地幔的流体如何进入浅层地下水区域。该项目还涉及社会效益，包括更广泛地了解断层强度的控制、地壳尺度水文以及建立破坏性应力的能力。深层地热系统和浅成热液金矿床之间的联系也得到了阐明。正在支持一名研究生接受最先进的地球物理仪器、现场勘测设计参数、偏远地区的实际后勤事务、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的教育。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，并且预计公众会对从加利福尼亚太平洋海岸附近到犹他州东部边界的科罗拉多高原内陆的潜在大横断面所提供的不同区域的剖面视图感兴趣。除了研究之外，该项目还支持博士生的研究生培训。来自大地电磁方法地球科学领域代表性不足的群体的学生。该研究的资金由美国国家科学基金会地球物理和构造项目提供。