Collaborative Research: Deciphering Sierran Magma Sources and Modes of Diversification Using Trace Element, O, and Hf Isotopic Analyses of Zircon

智力价值：美国中生代到新生代的大型科迪勒浴缸是地球上规模最大、最令人印象深刻的火成岩活动记录之一，代表了导致地壳主要增长期的复杂构造和火成岩过程的产物。对岩盆的现代跨学科研究改变了我们对大型大陆弧岩浆系统如何以及在什么时间尺度上发展的理解。在弧形背景下对地壳生长速度和收支的重要新限制，以及在弧形岩浆作用期间地幔和地壳之间的耦合和脱钩，从根本上改变了我们对弧形地球动力学的看法。然而，关于大型弧形岩浆系统的建造和多样化的模式、弧形中的大型岩浆室是常见的还是罕见的(或短暂的或长期的)、弧壳-地幔柱状岩浆在哪里获得其基本的地球化学/同位素特征以及这种特征在多大程度上反映了岩浆来源和/或在多大程度上被随后的开放系统岩浆作用所掩盖，仍然存在一些关键的悬而未决的问题。作为回答这些问题的一步，这个项目试图通过原位测量组成内华达山脉中部的几个大体积侵入体中的微量元素和锆石中的O和Hf同位素来评估弧状岩浆作用。这个项目解决的具体问题包括：(1)地壳和地幔成分对大陆弧岩浆的相对贡献是什么？(2)在什么深度(弧下地幔、下地壳、中地壳？)花岗岩类熔体获得其基本的地球化学和同位素特征吗？岩浆的不同成分是什么？(3)浅层地壳输入的地球化学和同位素特征有多少叠加在原生岩浆上？(4)大型、看似均质的深成岩浆是很好地混合的，还是由许多不同的注入作用组成的混合物？(5)最近对火山岩和深成岩的研究表明，它们由具有不同历史和来源的晶体组成。这种不均一性的程度和意义是什么？锆石是这项研究的重点，因为它是火成岩卓越的地壳地质年代学，而且它保留了丰富的其他信息，可以用来评估岩浆的起源。锆石的晶内地球化学和同位素变化以及锆石群体内的元素和同位素变化为岩浆演化提供了非常详细的记录。此外，由于Hf同位素是火成岩地幔提取年龄的敏感指标，而O同位素清楚地示踪地幔与表壳岩石对岩浆的贡献，锆石中Hf和O的联用分析已被证明是确定新地壳生长与地壳再循环体积的有力工具。拟议的工作将利用来自岩石学特征良好的深成岩体和内华达山脉中部侵入岩套的锆石同位素和微量元素记录来研究上述问题。与研究Tuolumne和John Muir侵入性套间的工作人员(Scott Patterson、Allen Glazner和同事)的特别合作旨在帮助解决关于深渊和浴缸如何组装的争论。广泛影响：该项目将为圣何塞州立大学(SJSU)的研究生和本科生以及波莫纳学院和其他四所克莱蒙特学院的本科生提供研究培训。学生将参与项目的所有阶段，最终在国家和可能的国际会议上展示他们的结果，并在参考期刊上发表他们的结果。波莫纳大学和上海州立大学都是主要的本科院校(上海州立大学也是少数族裔院校)。该项目还与一名在内华达山脉中部岩基工作了十多年的职业生涯中期科学家和一名初级教员合作，后者已经为理解岩基做出了重要贡献。该项目还将促进国际和机构间的合作，涉及加州大学洛杉矶分校、加州大学圣克鲁斯分校、斯坦福大学和阿姆斯特丹弗里耶大学的领先实验室。

Intellectual Merit: The large Mesozoic to Cenozoic US Cordilleran batholiths are among the most voluminous and impressive records of igneous activity on Earth and represent the product of complex tectonic and igneous processes that led to a major period of crustal growth. Modern interdisciplinary studies of the batholiths have transformed our understanding of how and on what time scale large continental arc magma systems develop. Important new constraints on the rates and budgets of crustal growth in arc settings and the coupling and decoupling between mantle and crust during arc magmatism have fundamentally changed our perception of arc geodynamics. Nevertheless, there remain critical unresolved issues concerning the mode of construction and diversification of large arc magma systems, whether large magma chambers in arcs are common or rare (or ephemeral or long-lived), where in the arc crust-mantle column magmas acquire their fundamental geochemical/isotopic signatures, and to what extent this signature reflects magmatic sources and/or is obscured by subsequent open system magmatic processes. As a step towards answering these questions, this project seeks to evaluate arc magmatic processes using in situ measurements of trace elements and O and Hf isotopes in zircon from several large-volume intrusions comprising the central Sierra Nevada batholith.Specific questions that this project addresses include: (1) what are relative contributions of crustal and mantle components to continental arc magmas? (2) At what depths (sub-arc mantle, lower crust, middle crust?) do granitoid melts acquire their fundamental geochemical and isotopic signatures, and what are the distinct components that contribute to the magmas? (3) How much of the geochemical and isotopic signature of shallow crustal input is superimposed on primary magmas? (4) Are large and seemingly homogeneous plutons well mixed, or are they amalgams of many discrete injections that do not interact? (5) Recent studies of volcanic and plutonic rocks suggest they consist of crystals having disparate histories and sources. What is the extent and significance of such heterogeneities?Zircon is the focus of this study because it is the preeminent crustal geochronometer for igneous rocks, and it retains a rich archive of other information that can be exploited to assess magma parentage. Intracrystalline geochemical and isotope variations in zircons and elemental and isotopic variation within populations of zircon have provided remarkably detailed records of magmatic evolution. In addition, because Hf isotopes are sensitive indicators of the mantle extraction age of igneous rocks, and O isotopes cleanly trace mantle versus supracrustal rock contributions to magmas, coupled analysis of Hf and O in zircons has proven to be a powerful tool for determining the volumes of new crustal growth versus recycling of crust. The proposed work will use zircon isotopic and trace element records from petrologically well-characterized plutons and intrusive suites in the central Sierra Nevada batholith to examine the questions posed above. Special collaborations with workers studying the Tuolumne and John Muir intrusive suites (Scott Patterson, Allen Glazner, and colleagues) are designed to help resolve debates on how plutons and batholiths are assembled.Broader Impacts: This project will provide research training for graduate andundergraduate students at San Jose State University (SJSU) and undergraduates at Pomona College and the other four Claremont Colleges. Students will be engaged in all stages of the project, ultimately presenting their results at national and possibly international conferences, and publishing their results in refereed journals. Pomona and SJSU are both primarily undergraduate institutions (SJSU is also a minority institution). The project also partners a mid-career scientist who has worked for over a decade in the central Sierra Nevada batholith with a junior faculty member who has already made important contributions to understanding of the batholith. This project will also foster international and inter-institutional collaborations involving leading labs at UCLA, UC-Santa Cruz USGS, Stanford, and Vrije University (Amsterdam).