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.

关于大陆地壳中母硅酸岩浆体形成的特征时空尺度，所提出的模型范围从构造增厚的富含流体的下地壳的部分熔融到岩浆底板，其中产生地壳熔融所需的热量是由基性岩质侵入（可能来自地幔源）产生的。这些模型预测了花岗岩岩浆产生的不同时间尺度。以地貌学为基础的下地壳缓慢平衡熔融模型表明，花岗岩是在数百万年的“造山”时间尺度上产生的。相比之下，岩浆底板的理论模型预测，与典型基性底板的结晶时间相当短的时间尺度（例如，对于几十到几百米厚的岩石侵入体来说，这是100-1000年的时间）产生的无水熔体。原则上，基性底板的侵入、与原位熔融相关的体积变化以及随后产生的花岗岩类岩浆的疏散都可以产生可观测到的大地测量变形。因此，在同时期大型活动岩浆体区域的大地测量可能对地壳深熔的时间尺度和动力学提供关键的约束。本项目利用干涉合成孔径雷达（InSAR）观测正在进行的地壳岩浆活动区域，以限制大规模熔体产生和/或迁移的典型速率，并测试提出的花岗岩熔体产生模型。观测到的岩浆诱发变形的空间模式和平均速率与理论建模相结合，理论建模明确包括熔化/冻结的热力学、宿主岩石力学性质的实际变化和非弹性变形，从而对地壳熔合动力学进行详细的定量理解。与模型结果相关的独立观测资料包括：地震成像对中地壳岩浆体横向范围和厚度的限制，地形学研究对岩浆隆升持续时间和总幅度的推断，以及挖掘出的古岩浆体的结构和地球化学特征。本文的研究成果与大陆地壳中下段“亮点”的地震观测解释、地壳岩浆活动的野外和理论研究、大陆地壳的起源和演化等有关。