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

关于大陆地壳中母硅质岩浆体形成的特征时空尺度的拟议模型，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通过镁铁质岩床的侵入(推测来自地幔源地)平流。这些模型预测了不同的花岗岩岩浆产生的时间尺度。基于温度学的下地壳缓慢平衡熔融模型表明，花岗岩是在几百万年量级的“造山”时间尺度上产生的。相比之下，岩浆底侵作用的理论模型预测，深熔熔体的产生时间相当短，仅相当于典型镁铁质底板结晶时间的量级(例如，对于几十米至几百米厚的基底岩，则为100-1000年)。原则上，镁铁质底板的侵入、与原地熔融有关的体积变化，以及随后产生的花岗岩类岩浆的疏散，都可以产生大地测量上可观察到的变形。因此，对同期大型活动岩浆体区域的大地测量可能对地壳深熔作用的时间尺度和动力学提供关键的限制。该项目使用正在进行的地壳岩浆活动地区的干涉合成孔径雷达(InSAR)观测，以限制大规模熔体产生和/或迁移的典型速率，并测试所提出的花岗岩熔体产生模型。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)、阿尔蒂普诺-普纳(南美洲)和藏南(亚洲)岩浆体。将观测到的岩浆引起的变形的空间模式和平均速率与明确包括熔融/冻结热力学、寄主岩石力学性质的实际变化和非弹性变形的理论模拟相结合，以发展对地壳深熔动力学的详细定量理解。对模型结果产生影响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，地貌研究对岩浆引起的抬升持续时间和总幅度的推断，以及出土的古代岩浆体的结构和地球化学特征。这项工作的结果对解释中下部陆壳“亮点”的地震观测、地壳岩浆作用的野外和理论研究以及陆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.