Collaborative Research: Examining the Temporal, Spatial and Geochemical Focusing of Magmatism During a Continental Arc Flare-up

大陆边缘火山弧是巨大的地壳生长工厂所在地，是大规模成矿存款形成的场所，也是广泛造山的地区。它们也是危险的火山爆发地点，随时可能在大片地区扰乱数百万人的生活。虽然对火山爆发有基本的了解，但对火山爆发的不同行为，如位置、数量和频率，还没有很好的了解。问题的一部分是，火山只是地球表面以下垂直延伸的岩浆管道系统中发生的复杂物理和化学过程的表面表现，这些岩浆管道系统为火山提供了燃料。一个重要的，但了解甚少的火山活动类型是这些系统的空间和时间的重点最好的火山领域记录，通过从最初的低容量，成分不均匀和空间分散的火山活动到高容量，均匀和空间集中的火山活动，往往导致大的火山爆发的变化表示。如果岩浆聚集开始于更深的地壳水平，那么是什么过程控制着这种现象，它如何在火山喷发的方式、位置、体积和频率上表现出来？ 为了回答这个问题，我们必须了解岩浆活动在地壳柱垂直迁移过程中集中的机制，以及火山和更深的岩浆系统如何相互联系。了解造成岩浆聚集的过程也将有助于我们了解矿石存款的形成和造山运动的各个方面以及大陆的生长。在加州的中部Sierra内华达州的初步研究中，有三个重要的发现：（1）在白垩纪的岩体中，有一个清晰的时空和地球化学岩浆聚集模式，其中约塞米蒂国家公园内的大型95 ~ 85 Ma Tuolumne侵入杂岩（TIC）位于岩浆聚集中心;（2）该地区的一些主岩悬体保存了与深成岩具有相同时间和地球化学聚焦的火山岩;（3）本区发育多个次火山斑岩“火山补给系统”，将同时代的火山岩场和深成岩场联系起来。 这些发现提供了机会，以调查潜在的原因和过程，促进岩浆集中在中上地壳，导致产生集中的火山系统，如那些建立在科罗拉多的圣胡安火山场或Aucanquilcha火山群在智利。拟议的研究将审查两个尺度：1）研究一个大型花岗岩体外围边界的火山和深成岩单元的广泛时空地球化学模式; 2）针对关键的深成岩-斑岩补给源-火山“三元组”，审查聚焦期间火山-深成岩的联系。拟议的研究将利用实地测绘、地球化学分析和地质年代学，探索古弧中6-11公里深处岩浆活动的空间/时间/成分聚焦，并与现代火山系统中的类似现象进行比较。该项目支持两名早期职业女性，南加州大学的博士生Ardill和CSU Fullerton的助理教授Memeti，以及南加州大学的Paterson教授。几个本科生和一个来自西班牙裔服务CSU富勒顿研究生将参与。一个免费的移动的应用程序将与CSU Fullerton助理教授Natalie Bursztyn博士合作开发，该应用程序将增强学生在地球科学方面的学习，并通过带他们进行虚拟实地考察，通过Sierra内华达州岩浆弧，吸引公众。该项目强调在国内和合作设施进行分析方法培训。Paterson和Memeti将继续与约塞米蒂国家公园进行为期12年的合作。

Continental margin volcanic arcs are locations of vast crustal growth factories, sites of extensive ore deposit formation and areas of widespread mountain building. They are also locations of dangerous volcanic eruptions that can disrupt the lives of millions of people at any time and over large regions. Although a basic understanding of volcanic eruptions exists, the different behaviors of eruption such as location, volumes and frequency are not well understood. Part of the problem is that volcanoes are only the surface expression of the complex physical and chemical processes that occur below the Earth's surface in vertically extensive magma plumbing systems that feed the volcanoes. One important but poorly understood type of volcanic behavior is the spatial and temporal focusing of these systems best documented in volcanic fields, as expressed through the change from initially low volume, compositionally heterogeneous and spatially spread-out volcanism to high volume, homogeneous and spatially focused volcanism often leading to large volcanic eruptions. If magma focusing begins at deeper crustal levels, what processes control this phenomenon, and how does it manifest itself in style, location, volume, and the frequency of volcanic eruptions? To answer this, it is essential that we understand the mechanisms by which magmatism is focused during vertical transport through the crustal column and how volcanic and deeper magmatic systems are linked to one another. Understanding the processes causing magma focusing will also help us understand ore deposit formation and aspects of mountain building and the growth of continents. Preliminary research in the central Sierra Nevada, California, has led to three important discoveries: (1) a clear pattern of spatiotemporal and geochemical magmatic focusing in a field of Cretaceous plutons with the large 95 to 85 Ma Tuolumne Intrusive Complex (TIC), in Yosemite National Park occurring at the center of the focus; (2) a number of host rock pendants in this area preserve volcanic rocks that mimic the same temporal and geochemical focusing as the plutons; (3) a number of subvolcanic porphyry "volcanic feeder systems" occur in this area, linking volcanic and plutonic fields of the same age. These discoveries provide the opportunity to investigate the potential causes and processes facilitating magma focusing in the mid-upper crust that leads to the generation of focused volcanic systems, like those established in the San Juan volcanic field in Colorado or the Aucanquilcha volcanic cluster in Chile. The proposed study will examine two scales: 1) Studying the broad spatiotemporal geochemical pattern of volcanic and plutonic units at the peripheral boundaries of a large silicic pluton; 2) Targeting key plutonic-porphyry feeder-volcanic "triads" to examine volcanic-plutonic links during the focusing. The proposed research will use field mapping, geochemical analyses and geochronology to explore spatial/temporal/compositional focusing of magmatism at 6-11 km depths in an ancient arc, and compare to similar phenomena established in modern volcanic systems. This project supports two early career women, PhD student Ardill at USC and assistant professor Memeti at CSU Fullerton, and professor Paterson from USC. Several undergraduates and one graduate student from Hispanic-Serving CSU Fullerton will be involved. A free mobile application will be developed in collaboration with CSU Fullerton assistant professor Dr. Natalie Bursztyn that will enhance student learning in the geosciences and engage the general public by taking them on a virtual field trip back in time through the Sierra Nevada magmatic arc. The project emphasizes training in analytical methods at home and at collaborating facilities. Paterson and Memeti will continue a 12 yr collaboration with Yosemite National Park.