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

内华达山脉南部地壳剖面弧形地壳生长和分异的过程和速率

• 批准号: 1552202
• 负责人: Oliver Jagoutz
• 金额: $ 32万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1552202&HistoricalAwards=false
• 关键词: Processes; Rates; Arc; Crust; Growth

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.

在俯冲区域的岩浆弧的结构在地球上新的大陆壳的创建中起着至关重要的作用。特别是，假设弧的下层地壳（30 km深度）中的许多不同机制对于形成长英质大陆地壳至关重要。但是，在全球范围内，在这些深度处形成的岩石在地面上被限制的位置是提高我们对这些过程中化学和物理控制的理解以及发生的时间尺度的基本限制。该提案旨在通过对最南端的内华达州山地石中相对较少研究的较低地壳岩石的暴露，将田间观测，主要，痕量元素和同位素地球化学以及高精度地球量学的相结合，对这些过程进行评估。该项目中的研究活动将与本科生的领域和分析经验融合在一起，而发现将纳入本科课程。通过与Tejon Ranch Conservancy的合作，计划帮助开发Tejon Ranch物业的外展计划和教育材料。这些计划包括牧场的地质之旅，并将涵盖板块构造和弧形岩浆主义的基础知识，以及加利福尼亚的地质历史。 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内华达山脉有限。然而，内华达山脉还包含一个独特的地壳部分，暴露了一个结构连续的截面，从〜7-37 km的深度延伸，并在约100 mA的同时出现了一套火成岩岩石，与晚期的Crela sierra sierra sierra sierra nevada岩浆岩浆爆发。本节提供了一个理想的位置，以评估不同模型的较低地壳过程，包括分数结晶和部分融化主导的深层地壳热区域，循环含糊不足和对浮力材料的伴随。结构上连续和同时扩展的露头的结合将使我们能够更好地描述这些过程及其相关时间尺度，并评估它们对产生Felsic Continental Crust的重要性。这些发现将对我们对美国西部的中生代历史的理解以及验证大陆下层地壳的地震观察有更多的重要意义。