Processes and Rates of Arc Crust Growth and Differentiation in the Southern Sierra Nevada Crustal Section

俯冲带岩浆弧的形成对地球上新陆壳的形成起着至关重要的作用。特别是，弧形下部地壳(30公里深)中的一些不同机制被假设为对长英质陆壳的形成至关重要。然而，世界各地在这些深度形成的岩石暴露在地表的地点有限，这从根本上限制了我们对这些过程的化学和物理控制以及发生这些过程的时间尺度的理解。这项提议旨在通过对内华达山脉最南端岩基下部地壳岩石的相对较少研究的详细研究，结合实地观察、常量、微量元素和同位素地球化学以及高精度地质年代学，来评估这些过程。该项目的研究活动将与本科生的实地和分析经验相结合，同时研究成果将被纳入本科课程。通过与Tejon牧场保护协会的合作，计划帮助为Tejon牧场财产开发外展计划和教育材料。这些项目包括牧场的地质之旅，将涵盖板块构造和弧形岩浆作用的基础知识，以及加利福尼亚州的地质历史。这些计划将面向普通公众，并专门针对公立学校，服务于特哈查皮/贝克尔斯菲尔德地区主要未被充分代表的少数族裔人口。内华达山脉基岩是大陆弧深成作用研究最深入的例子之一，但几乎整个裸露山脉的样本都是在浅至中地壳压力下形成的，因此我们对内华达山脉下地壳过程的了解有限。然而，内华达山脉也包含一个独特的地壳剖面，暴露出一段从7-37公里深度延伸的构造连续剖面，并包含一套在~100 Ma同时侵位的火成岩，与晚白垩世内华达山脉岩浆爆发事件相吻合。这一节为评价下地壳过程的不同模型提供了一个理想的地点，这些过程包括以分离结晶和部分熔融为主的地壳深部热区、旋回俯冲和浮力物质的重新分层。构造连续和同期侵位露头的组合将使我们能够更好地描述这些过程及其相关的时间尺度，并评估它们对长英质陆壳形成的重要性。这些发现将对我们理解美国西部中生代历史和验证大陆下地壳的地震观测具有额外的重要意义。

The construction of magmatic arcs at subduction zones plays a critical role in the creation of new continental crust on Earth. In particular, a number of different mechanisms in the lower crust (30 km depth) of arcs are hypothesized to be critical for the formation of felsic continental crust. However the restricted number of locations worldwide where rocks formed at these depths are exposed on the surface is a fundamental limitation to improving our understanding of the chemical and physical controls on these processes and the time scales over which they occur. This proposal aims to evaluate these processes through a detailed study of a relatively little studied exposure of lower crustal rocks in the southernmost Sierra Nevada batholith, combining field observations, major, trace element and isotope geochemistry, and high precision geochronology. The research activities in this project will be integrated with field and analytical experiences for undergraduates while findings will be incorporated into undergraduate courses. Through collaboration with the Tejon Ranch Conservancy, it is planned to help develop outreach programs and education materials for the Tejon Ranch property. These programs include geologic tours of the ranch, and will cover both the basics of plate tectonics and arc magmatism, as well as the geologic history of California. The programs will be available to the general public, and be specifically targeted to public schools serving the primarily underrepresented minority populations in the Tehachapi/Bakersfield region.The Sierra Nevada Batholith is one of the best-studied examples of continental arc plutonism, but nearly the entire exposed range samples rocks formed at shallow to middle crustal pressures, and as a result our understanding of lower crustal processes in the Sierra Nevada are limited. However, the Sierra Nevada also contains a unique crustal section, exposing a structurally continuous section extending from ~7-37 km depth, and containing a suite of igneous rocks emplaced contemporaneously at ~100 Ma, coinciding with the Late Cretaceous Sierra Nevada magmatic flare-up event. This section provides an ideal location to evaluate different models for lower crustal processes including fractional crystallization and partial melting dominated deep crustal hot zones, cyclic underthrusting and relamination of buoyant material. The combination of structurally continuous and contemporaneously emplaced outcrop will allow us to better characterize these processes and their relevant timescales, and to assess their importance for the generation of felsic continental crust. These findings will have additional important implications for our understanding of the Mesozoic history of the western US, and for validating seismic observations of continental lower crust.