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?.

详细了解大陆边缘火山之下的岩浆管道系统，对于了解大陆地壳的演化和生长及其对地壳变形和矿床形成的相关影响至关重要。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喷发和相关灾害的空间分布、类型和频率。尽管我们对大陆边缘深部岩浆作用的了解正在极大地提高，但关于次火山岩浆储集层中大量岩浆体积的规模甚至存在、岩浆体之间通过大陆地壳厚度相互联系以及改变这种岩浆化学的过程的重要性和程度的争论仍在继续。这项研究的目的是通过研究加州约塞米蒂国家公园暴露出来的深成岩浆--在深处形成的古老岩浆岩--来调查这些失踪但关键的拼图碎片。传统的块状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，本研究的目标是通过对深成岩体中单个晶体的微尺度地球化学分析来解决这些问题。这项研究还将为数值模拟工作提供更好的数据，并具有指导未来深成岩研究的巨大潜力。这项研究将使用结构受限的元素和同位素地球化学分析方法，对从吐鲁门侵入杂岩战略选定的地点进行成分不均匀的成岩和副矿物。它曾经是一个复合型的中地壳弧形岩浆储集层--以检验以下假设。(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)中地壳油气藏中存在相互连通的岩浆混杂带。(3)富晶岩浆发生在深部注入岩浆与共生的混杂岩浆带之间。(4)结晶-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。通过验证这些假设，可以评估中地壳弧状深成岩的两个模型。一个岩墙模型预测，岩浆在地壳深部热区获得了化学特征？并迅速上升为次火山岩储集层，不产生大型岩浆体。岩浆泥柱模型预测，岩浆形成垂直扩展的储集层，并在许多地壳水平上经历成分改造。矿物分析将有助于识别不同的矿物群体，解释普遍的岩浆过程，评估同时代岩浆的存在或不存在及其规模，以及此类岩浆的化学沟通能力。