InSAR Measurements and Theoretical Modeling of Deformation due to Large Mid-crustal Magma Bodies: Investigation of the Dynamics and Timescales of Crustal Anatexis

InSAR 测量和大型中地壳岩浆体变形的理论建模：研究地壳深熔的动力学和时间尺度

• 批准号: 0208165
• 负责人: Yuri Fialko
• 金额: $ 20.18万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-07-01 至 2006-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0208165&HistoricalAwards=false
• 关键词: InSAR; Measurements; Theoretical; Modeling; Deformation

FialkoEAR-0208165The proposed models regarding characteristic spatiotemporal scales of formation of parental silicic magma bodies in the continental crust range from partial melting of the tectonically thickened fluid-rich lower crust to magmatic underplating, whereby the heat required to produce crustal melting is advected by intrusions of mafic sills (presumably, from the mantle source). These models predict very different time scales for the production of granitic magma. The pertologically-based model of slow equilibrium melting of the lower crust implies that granites are generated on "orogenic'' time scales of the order of millions of years. In contrast, theoretical models of magmatic underplating predict that anatectic melts are produced on quite short timescales of the order of the crystallization time of typical mafic underplates (e.g., 100-1000 years for sill intrusions that are a few tens to a few hundred meters thick). In principle, the intrusion of mafic underplates, the volume changes associated with in situ melting, and the subsequent evacuation of the resulting granitoid magmas can each generate geodetically observable deformation. Geodetic measurements in areas of contemporaneous large active magma bodies may therefore provide critical constraints on the timescales and dynamics of crustal anatexis. This project uses Interferometric Synthetic Aperture Radar (InSAR) observations in regions of the ongoing crustal magmatism to constrain typical rates of the large-scale melt generation and/or migration, and to test the proposed models of the granitic melt production. The primary targets include large mid-crustal magma bodies imaged by seismic studies, in particular, the Socorro (New Mexico, USA), the Altiplano-Puna (South America), and the Southern Tibet (Asia) magma bodies. The observed spatial patterns and average rates of magma-induced deformation are combined with theoretical modeling that explicitly includes thermodynamics of melting/freezing, realistic variations in the mechanical properties of the host rocks, and inelastic deformation, to develop a detailed quantitative understanding of the dynamics of crustal anatexis. Independent observables that are brought to bear on the model results include constraints on the lateral extent and thickness of the mid-crustal magma bodies from seismic imaging, inferences about the duration and total amplitude of the magma-induced uplift from geomorphologic studies, and structural and geochemical signatures of the exhumed ancient magma bodies. Results of this work are relevant to interpretations of seismic observations of "bright spots'' in the mid-to-lower continental crust, field and theoretical studies of the crustal magmatism, and origin and evolution of the continental crust.

FialkoEAR-0208165提出的关于大陆地壳中硅质岩浆体形成的特征时空尺度的模型范围从构造上增厚的富含流体的下地壳的部分熔融到岩浆底侵，其中产生地壳熔融所需的热量是通过平流侵入镁铁质基岩（可能来自地幔源）。这些模型预测了花岗质岩浆产生的非常不同的时间尺度。基于岩石学的下地壳缓慢平衡熔融模型表明，花岗岩是在数百万年量级的“造山”时间尺度上生成的。相比之下，岩浆底侵理论模型预测深熔熔体是在相当短的时间内产生的。典型镁铁质底板结晶时间的时间尺度（例如，数十到数百米的岩床侵入物为 100-1000 年）原则上，镁铁质底板的侵入、与原位熔化相关的体积变化以及随后产生的花岗岩岩浆的疏散都可以在同时期大型活动岩浆体区域产生大地测量可观测的变形。地壳深熔的时间尺度和动力学的关键限制该项目在该地区使用干涉合成孔径雷达（InSAR）观测。正在进行的地壳岩浆作用，以限制大规模熔体生成和/或迁移的典型速率，并测试所提出的花岗岩熔体生产模型。主要目标包括通过地震研究成像的大型中地壳岩浆体，特别是索科罗（美国新墨西哥州）、高原-普纳（南美洲）和西藏南部（亚洲）岩浆体。 观察到的岩浆诱发变形的空间模式和平均速率与明确包括熔化/冻结热力学、主岩机械性能的实际变化以及非弹性变形的理论模型相结合，以形成对动力学的详细定量理解地壳深熔作用。对模型结果产生影响的独立观测值包括地震成像对中地壳岩浆体横向范围和厚度的限制、地貌研究中对岩浆引起的隆起的持续时间和总幅度的推断以及构造和挖掘出的古代岩浆体的地球化学特征。该工作成果涉及中下陆壳“亮点”地震观测解释、地壳岩浆作用的现场与理论研究、陆壳起源与演化等。