EVALUATING THE ROLE OF MASH PROCESSES AND THE GROWTH OF CONTINENTAL CRUST

地球的独特之处之一是它包含了由大陆地壳组成的大片陆地或大陆。大陆地壳对社会很重要，因为它富含用于建筑，制造业，农业和能源的矿物和岩石。因此，了解大陆是如何形成的对我们世界经济的成功至关重要。大陆地壳通常被认为是在两个构造板块会聚的俯冲带形成的，其中一个板块被俯冲到另一个板块之下。在这些环境中，地幔（地壳下面的一层）的熔化被认为是大陆地壳生成的结果。这个模型的一个主要的未解决的问题是，地幔的直接熔融产生的熔体是地球化学上不同的相对于大块大陆地壳的估计。这一难题引出了这一提议的核心问题：地壳最深处的什么过程导致了来自底层地幔的熔体的转化/富集？该项目通过研究地球上少数几个可以直接观察古代俯冲带大陆地壳深层根源的地方之一来解决这个问题。我们专注于位于新西兰南岛西南部的峡湾国家公园中暴露的岩石，在那里古老俯冲带的深部地壳暴露于40至65公里的古深度。我们的团队与新西兰研究人员合作，将使用地球化学和同位素数据以及数值模拟来确定这些熔体的地球化学演化过程。我们的项目的结果将提供新的见解，在现代俯冲带，这是地质学家无法访问的地壳深部的岩浆过程中运作。该项目还将通过一个创新的外展计划来推动社会成果，该计划通过研究为加州州立大学北岭分校的代表性不足的学生提供指导，北岭分校是洛杉矶县的一个西班牙裔服务机构和一个亚裔美国土著-太平洋岛民服务机构。该项目还将为研究生和本科生提供国际实地经验，并接触尖端的分析研究设施，这将有助于发展多元化，具有全球竞争力的STEM劳动力。自1988年Hildreth和Moorbath首次提出以来，“MASH”概念对有关大陆弧系统演化的火山学、岩石学和构造学思想产生了深远的影响。MASH带最初被认为是位于壳幔边界的“熔融、同化、储存和均质化”区域，在这里弧岩浆获得了它们的能量。地壳？通过壳内重熔和现有地壳的清除而产生的特征。虽然MASH带通常在大陆弧模型中被引用，但很少有研究直接研究MASH带所在的大陆弧深根的岩浆过程。该项目的总体目标是了解进入地壳深部“MASH”区的熔体的起源以及导致这些熔体的地球化学多样化的过程。我们的项目包括有针对性的实地测绘和采样，全岩和矿物地球化学，以及Malaspina岩体（Fiordland，新西兰）的高精度U-Pb锆石定年，该岩体位于约40-50 km的古深度。我们使用新的和现有的样品来解决三个关键问题，具体到下地壳的中位玄武岩：1）弧岩浆如何以及在哪里获得他们的“大陆”地壳签名？2)MASH区在低地壳熔体中的作用有多大？熔体在下地壳MASH带中储存了多长时间，它们以什么速率分化？这些问题的答案将有助于深入了解导致会聚边缘环境中大陆地壳生长的过程。该项目还为“ROCs”外展计划（CSUN学生的研究机会）提供持续支持。该计划的目标是1）鼓励有抱负的CSUN地质本科生，特别是少数民族和女性，与教师导师一起从事研究项目，2）拓宽学生？了解地球科学的职业和研究生院的机会，以及3）创造一种社区意识，以提高地球科学的保留率。ROCs计划的第二阶段将创建一个由前ROCs参与者组成的地球科学导师网络，他们将返回CSUN分享他们在研究生院和行业的经验。这一努力将建立目前代表性不足的CSUN学生和洛杉矶地区及其他地区的应届毕业生之间的联系。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

One of the unique features of Earth is that it contains large land masses, or continents, consisting of continental crust. Continental crust is important to society because it is enriched in minerals and rocks that are used in construction, manufacturing, agriculture and energy. Thus, understanding how continents form is vital to the success of our world economy. Continental crust is generally thought to form in subduction zones where two tectonic plates converge, and one plate is underthrusted beneath another. In these settings, melting of the mantle (the layer below the crust) is thought to result in the generation of continental crust. One of the major unresolved problems with this model is that direct melting of the mantle produces melts that are geochemically distinct relative to estimates for bulk continental crust. This conundrum leads to the central question of this proposal: what processes in the deepest parts of the crust lead to the transformation/enrichment of melts derived from the underlying mantle? This project addresses this problem by examining one of the few places on Earth where it is possible to directly observe the deep roots of continental crust in an ancient subduction zone. We focus on rocks exposed in Fiordland National Park located in the southwestern part of the South Island, New Zealand, where the deep crust of an ancient subduction zone is exposed to depths of 40 to 65 km paleodepth. Our group, in collaboration with New Zealand researchers, will use geochemical and isotopic data together with numerical modeling to determine the processes responsible for the geochemical evolution of these melts. The results of our project will provide new insights into the magmatic processes operating in the deep crust of modern subduction zones, which are inaccessible to geologists. The project will also advance societal outcomes through an innovative outreach program that provides mentorship through research to underrepresented students at California State University Northridge, a Hispanic Serving and an Asian American Native American-Pacific Islander Serving Institution in Los Angeles County. This project will also provide graduate and undergraduate students with international field experiences and exposure to cutting-edge analytical research facilities that will aid in the development of a diverse, globally competitive STEM workforce. Since first proposed by Hildreth and Moorbath in 1988, the "MASH" concept has had a profound impact on volcanological, petrological and tectonic thinking regarding the evolution of continental-arc systems. MASH zones as originally conceived were defined as "Melting, Assimilation, Storage and Homogenization" regions located at the crust-mantle boundary where arc magmas acquired their ?crustal? signature through intracrustal remelting and scavenging of existing crust. Although MASH zones are commonly invoked in continental-arc models, there have been few studies that have directly examined magmatic processes in the deep roots of continental arcs where MASH zones are located. The overarching goal of this project is to understand the origin of melts that enter deep-crustal "MASH" zones and the processes that lead to geochemical diversification of these melts. Our project involves targeted field mapping and sampling, whole-rock and mineral geochemistry, and high-precision U-Pb zircon dating of the Malaspina Pluton (Fiordland, New Zealand), which was emplaced at ~40-50 km paleodepth. We use new and existing samples to address three key questions specific to the lower crust of the Median Batholith:1) How and where do arc magmas acquire their "continental" crustal signature? 2) How efficient are MASH zones in homogenizing lower-crustal melts? and, 3) How long are melts stored and at what rate do they differentiate in lower-crustal MASH zones? The answers to these questions will provide insights into the processes that lead to the growth of continental crust in convergent margin settings. This project also provides continued support for the "ROCs" outreach program (Research Opportunities for CSUN students). Goals of this program are to 1) encourage aspiring CSUN geology undergraduate students, especially minorities and females, to pursue research projects with faculty mentors, 2) broaden students? understanding of career and graduate school opportunities in the geosciences, and 3) create a sense of community with the goal of increasing retention in geoscience. Phase 2 of the ROCs program will create a network of geoscience mentors from former ROCs participants who will return to CSUN to share their experiences in graduate school and industry. This effort will build ties between current underrepresented CSUN students and recent graduates in the Los Angeles area and beyond.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.