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

关于大陆地壳中母岩浆体形成的时空尺度特征，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侵，由此产生地壳熔融所需的热量由镁铁质岩床的侵入平流输送（据推测，来自地幔源）。这些模型预测了花岗岩岩浆产生的非常不同的时间尺度。下地壳缓慢平衡熔融的地质学模型意味着花岗岩是在数百万年的“造山”时间尺度上形成的。相比之下，岩浆底侵作用的理论模型预测，深熔熔体是在相当短的时间尺度上产生的，大约是典型的镁铁质底侵作用的结晶时间（例如，对于几十到几百米厚的岩床侵入体，100-1000年）。原则上，镁铁质底板的侵入、与原位熔融相关的体积变化以及由此产生的花岗岩类岩浆的随后疏散都可以产生大地测量学上可观察到的变形。因此，在同生的大型活动岩浆体地区进行大地测量，可能会对地壳深熔的时间尺度和动力学提供关键的约束。 该项目使用干涉合成孔径雷达（干涉合成孔径雷达）观测正在进行的地壳岩浆活动的地区，以限制典型的大规模熔体生成和/或迁移率，并测试花岗岩熔体生产的拟议模型。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Socorro（新墨西哥州，美国），Altiplano-Puna（南美洲）和西藏南部（亚洲）岩浆体。 所观察到的空间格局和平均速率的岩浆引起的变形相结合的理论建模，明确包括热动力学的熔融/冻结，现实的变化的力学性质的主机岩石，和非弹性变形，开发一个详细的定量了解地壳深熔的动力学。独立的观测，带来了承担的模型结果，包括限制的横向范围和厚度的中地壳岩浆体的地震成像，推断的持续时间和总振幅的岩浆引起的隆起地貌研究，和结构和地球化学特征的挖掘古岩浆体。这一工作成果对大陆中下地壳“亮点”地震观测资料的解释、地壳岩浆活动的野外和理论研究以及大陆地壳的起源和演化具有重要意义。

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.