Modes of Lithospheric Extensional Consumption and Magmatism: Testing for End-member Cases at the Great Basin-Colorado Plateau Transition with a Magnetotelluric Resistivity Transect

岩石圈伸展消耗和岩浆作用模式：用大地电磁电阻率断面测试大盆地-科罗拉多高原过渡区的端元情况

• 批准号: 0230027
• 负责人: Philip Wannamaker
• 金额: $ 15.48万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-03-01 至 2007-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0230027&HistoricalAwards=false
• 关键词: Modes; Lithospheric; Extensional; Consumption; Magmatism

EAR-0230027WannamakerEAR02-30027: Modes of lithospheric extensional consumption and magmatism: testingfor end-member cases at the Great Basin-Colorado Plateau transition, Utah, with amagnetotelluric resistivity transectP.I.: Philip E. Wannamaker (University of Utah, Energy & Geoscience Institute, 423Wakara Way, Suite 300, Salt Lake City, UT 84108, [e-mail])AbstractEnd-member possibilities for stable lithospheric extension will be tested according totheir influence on physical properties of the deep crust and upper mantle across the GreatBasin-Colorado Plateau transition zone, south-central Utah. The main geophysicalproperty to be investigated is electrical conductivity, together with its implications forthermal and rheological state, which will be imaged using the magnetotelluric (MT)technique. New MT surveying primarily across the transition zone (TZ) per se will joinexisting data into an E-W transect nearly 400 km in length, with a depth range ofsensitivity from 100's of m to 250-400 km approximately. Data will be acquired usingwideband and long-period recorders of the University of Utah and University ofWashington, which reside in the NSF-supported EMSOC instrument facility. Existinggeophysical indicators show a strong N-S strike orientation at upper crustal tolithospheric scales and should allow accurate cross sections of model conductivity usingmainly current 2-D regularized inversion platforms. Substantially reduced electricalresistivity values at lower crustal and upper mantle depths inferred from MT fielddata most likely reflect melts and exsolved ionic fluids. Previous surveying indicatesthat the onset of low resistivity in the deep crust occurs for T ~500-550 o C in high-grademetaigneous host rocks. Depth variation in low resistivity thus will approximatean isotherm which should evolve gradually from the GB to the CP in the case ofuniform TZ warming, or show an upwelling under the little-extended TZ in the caseof non-uniform, enhanced extension at depth. Exsolved fluids weaken the lithospheregreatly through diffusion creep, so resistivity will provide a clear view of at leastrelative rheological contrasts. Conductivity, heat flow and constraints on compositionand timing of extension, will be used in time-dependent, 2-D thermal modeling for animproved projection of the thermal field into the upper mantle.

EAR-0230027WannamakerEAR02-30027：岩石圈伸展消耗和岩浆作用的模式：使用大地磁电阻率横断面测试犹他州大盆地-科罗拉多高原过渡区的终端成员案例主要负责人：Philip E. Wannamaker（犹他大学能源与地球科学研究所，423Wakara Way，Suite 300，盐湖城） City, UT 84108, [e-mail]）摘要将根据其对犹他州中南部大盆地-科罗拉多高原过渡区深部地壳和上地幔物理性质的影响来测试稳定岩石圈伸展的最终成员可能性。要研究的主要地球物理特性是电导率及其对热和流变状态的影响，将使用大地电磁 (MT) 技术对其进行成像。主要跨越过渡区 (TZ) 本身的新 MT 测量将把现有数据加入到近 400 公里长的东西向横断面中，灵敏度深度范围从 100 米到大约 250-400 公里。数据将使用犹他大学和华盛顿大学的宽带和长周期记录仪采集，这些记录仪位于 NSF 支持的 EMSOC 仪器设施中。现有的地球物理指标显示在上地壳岩石圈尺度上有很强的南北走向方向，并且应该允许使用主要使用当前二维正则反演平台的模型电导率的精确横截面。从 MT 现场数据推断出的下地壳和上地幔深度处的电阻率值大幅降低，很可能反映了熔体和溶出的离子流体。前期勘测表明，地壳深部低电阻率在高品位变火成岩围岩温度~500-550 o C时开始出现。因此，低电阻率的深度变化将近似等温线，在均匀的 TZ 变暖的情况下，该等温线应该从 GB 逐渐演化到 CP，或者在深度不均匀、增强的扩展的情况下，在小扩展的 TZ 下显示出上升流。溶解的流体通过扩散蠕变极大地削弱了岩石圈，因此电阻率将至少提供相对流变对比的清晰视图。电导率、热流以及对成分和延伸时间的限制将用于与时间相关的二维热建模，以改进将热场投射到上地幔中。