Collaborative Research: Crustal Overturn in Continental Margin Arcs During Magmatic Surges

俯冲带，即岩石圈板块在回到地幔之前滑到另一个板块下面的地方，导致深处的岩石融化，这些融化物的上升形成了长长的火山链和次火山岩链，它们一起被称为岩浆弧。由于这些弧和周围的宿主岩石是热的，并且由于板块运动而受到巨大的应力，它们被广泛变形，形成了造山带。大陆边缘造山带及其伴生岩浆弧的演化具有非稳态、非定速、非定速的特征。俯冲、造山、岩浆作用、掘出和侵蚀/再沉积。本研究项目考察了这一速度的细节，特别是在岩浆涌动（大量岩浆形成并加入地壳的时期）期间，以及构造将容易融化的地壳运送到俯冲带中发生融化的深度区域所起的作用。目的是验证这样一个假设，即在白垩纪中期（105-85 Ma）高岩浆涌动时期，内华达山脉南部和萨利尼亚地块的大部分弧被安置在一个地壳尺度的对流系统中。对105 ~ 85 Ma左右岩体垂坠的初步研究表明，在岩浆活动的上升过程中，变质沉积岩和溢流变质火山寄主岩石被对流翻转，并经历了快速的向下位移和高应变流动。该研究将扩展和综合大量数据集（例如，实地研究、地质年代学、气压学、垂直位移、应变场、岩浆通量），并进行广泛的正演数值、热力学建模，能够将岩浆上升、粘弹塑性宿主行为、大应变、非线性流变学和现实相变结合起来，以了解该过程的物理特性。火山爆发对人类社会产生了巨大的影响，在大气的形成和气候变化中都起着巨大的作用。此外，造山带的地壳变形会导致地震等短期事件和造山等长期事件，这些事件也会影响我们的社会。认识到弧壳有时会发生翻转，从而将地壳物质纳入上升的岩浆中，将极大地改变对岩浆系统、这些系统的地球化学和地质年代学分析以及地壳生长速度的理解。这项研究将增进对这些系统的了解，并将向公众提供基于地理信息系统的关于地质年代学、热气压计、垂直位移率、应变和应变率以及岩浆通量的数据库。来自多个机构的大量本科生将通过南加州大学团队研究计划参与研究项目

Subduction zones, where one lithospheric plate slides beneath another before returning to the mantle, results in melting of rock at depth and the rise of these melts to form long chains of volcanoes and subvolcanic plutons that together are called magmatic arcs. Because these arcs and surrounding host rocks are hot and undergoing tremendous stresses due to the plate motions they become extensively deformed forming orogenic belts. The evolution of continental margin orogenic belts and their associated magmatic arcs has a non-steady state ?tempo? of subduction, orogeny, magmatism, exhumation, and erosion/redeposition. This research project examines the details of this tempo particularly during magmatic surges (periods when large volumes of magma are formed and added to the crust) and what role was played by the tectonic transport of easily melted crust to regions at depth where melt occurs in subduction zones. The goal is to test the hypothesis that during the mid-Cretaceous (105-85 Ma) high magma surge episode much of the arc in the southern Sierra Nevada and Salinian blocks was emplaced within a crustal scale convection system. Preliminary studies of pendants around 105-85 Ma plutons indicate that, during rise of magmatism, metasedimentary and effusive metavolcanic host rocks were convectively overturned and underwent rapid downward displacement and high-strain flow. The research will expand and synthesize a number of data sets (e.g., field studies, geochronology, barometry, vertical displacement, strain fields, magma fluxes) plus perform extensive forward numerical, thermomechanical modeling capable of incorporating magma ascent, viscoelasto- plastic host behavior, large strains, nonlinear rheologies, and realistic phase transitions to understand the physics of the process.Volcanic eruptions dramatically impact human society and play a huge role in both the formation of our atmosphere and in climate change. Additionally crustal deformation in orogenic belts leads to short-term events such as earthquakes and long-term events such as mountain building that also impact our society. The recognition that arc crust, at times, undergoes overturn thus incorporating crustal materials into rising magmas will dramatically change the understanding of magmatic systems, the geochemical and geochronologic analyses of these systems, and rates of crustal growth. This research will improve understanding of these systems and the GIS based databases produced on geochronology, thermobarometry, vertical displacement rates, strain and strain rates, and magma fluxes will be made available to the public. A large number of undergraduates from several institutions will be involved in the research project through the University of Southern California Team Research program