Collaborative Research: Testing the Existence of Magma Mush Zones and Potential Processes of Magma Differentiation in the Mid-crust with In situ Mineral Geochemistry

合作研究：用原位矿物地球化学测试中地壳中岩浆糊状带的存在和岩浆分异的潜在过程

• 批准号: 1550935
• 负责人: Valbone Memeti
• 金额: $ 18.66万
• 依托单位: CSU Fullerton Auxiliary Services Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-03-01 至 2020-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1550935&HistoricalAwards=false
• 关键词: Collaborative; Research; Testing; Existence; Magma

Detailed knowledge of magma plumbing systems beneath continent-margin volcanoes is crucial for understanding the evolution and growth of continental crust and the associated effects on crustal deformation and ore deposit formation. Understanding the time and length scales of processes in the magma plumbing system sheds light on the spatial distribution, type and frequency of volcanic eruptions and associated hazards. Although our understanding of continent-margin magmatism at depth is vastly improving, debate continues as to the dimensions, and even existence, of large magma volumes in sub-volcanic magma reservoirs, the interconnectivity between magma bodies through the thickness of the continental crust, and the importance and extent of processes that modify the chemistry of such magmas. The aim of this study is to investigate these missing, but critical pieces of the puzzle through study of plutons - ancient magmatic rocks formed at depth - as exposed in Yosemite National Park, California. Traditional bulk-rock element and isotope analyses have left too many fundamental questions about the architecture of crustal magmatic systems, resolution of which is a goal of this study through a new approach of utilizing micro-scale geochemical analysis of individual crystals in plutons. This research will also provide better data for numerical modeling efforts and has great potential to guide future studies of plutonic rocks.This study will use texturally-constrained, element and isotope geochemical analysis of compositionally heterogeneous rock-forming and accessory minerals from strategically selected sites of the Tuolumne Intrusive Complex ? which was once a composite, mid-crustal arc magma reservoir - to test the following hypotheses. (1) Mineral zoning and inclusion relationships in plutonic rocks record distinct, decipherable magmatic histories. (2) Interconnected magma mush zones exist in mid-crustal reservoirs. (3) Mixing of crystal-rich magmas occurs between magmas injected from deeper levels and coexisting mush zones. (4) Crystal-liquid separation is an important process in the middle crust; consequently, many plutonic rocks are cumulate and do not represent liquid compositions. Testing these hypotheses will allow assessment of two models for mid-crustal arc plutons. A dike model predicts that magmas attain their chemical signatures in deep-crustal ?hot zones? and rise rapidly to sub-volcanic reservoirs without producing large magma bodies. A magma mush column model predicts that magmas form vertically-extensive reservoirs and undergo compositional modification at many crustal levels. Mineral analysis will allow identification of distinct mineral populations, interpretation of prevalent magmatic processes, assessment of the presence or absence of coeval magmas and their dimensions, and the ability of such magmas to chemically ?communicate?.

详细了解陆缘火山岩浆管道系统对于了解陆壳的演化和生长及其对地壳变形和矿床存款形成的影响至关重要。了解岩浆管道系统中过程的时间和长度尺度有助于了解火山爆发的空间分布、类型和频率以及相关危害。虽然我们对大陆边缘深部岩浆活动的认识有了很大的提高，但关于次火山岩浆库中大量岩浆的规模，甚至是否存在，通过大陆地壳厚度的岩浆体之间的相互联系，以及改变这种岩浆化学性质的过程的重要性和程度，仍有争议。这项研究的目的是通过研究在加州的约塞米蒂国家公园暴露的深成的古老岩浆岩来调查这些缺失的、但关键的拼图碎片。传统的整体岩石元素和同位素分析留下了太多关于地壳岩浆体系结构的基本问题，解决这些问题是本研究的一个目标，通过一种新的方法，利用微尺度地球化学分析的单个晶体在岩体中。这项研究也将提供更好的数据，数值模拟的努力，并有很大的潜力，以指导未来的研究深成岩。这项研究将使用纹理约束，元素和同位素地球化学分析的成分不均匀的成岩和辅助矿物的战略选择网站的Tuolumne侵入杂岩？它曾经是一个复合的中地壳弧岩浆库，以验证以下假设。(1)深成岩中的矿物分带和包裹体关系记录了不同的、可解释的岩浆历史。(2)中地壳储层中存在相互连通的岩浆泥带。(3)富晶体岩浆的混合发生在从更深层次注入的岩浆和共存的泥质带之间。(4)晶体-液体分离是中地壳的一个重要过程，因此，许多深成岩是堆积的，不代表液体成分。测试这些假设将允许两个模型的中地壳弧岩体的评估。岩脉模型预测岩浆在地壳深处获得其化学特征？热点地区？并迅速上升到次火山储层，而不产生大的岩浆体。一个岩浆泥柱模型预测，岩浆形成垂直广泛的水库，并在许多地壳水平进行成分修改。矿物分析将允许识别不同的矿物种群，解释普遍的岩浆过程，评估是否存在同时代的岩浆及其尺寸，以及这种岩浆的化学？沟通？