Collaborative Research: "SUPERERUPTIONS," MAGMA CHAMBERS, & PLUTONIC RESIDUE: Insights from Peach Spring Tuff, Significance of Sphene

“该奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。”学术价值：“超级喷发”--产生450千米岩浆的爆炸性喷发--可以说是地球上所有自然过程中最具灾难性的。它们在目前关于地壳岩浆活动性质的辩论中发挥着核心作用。对超喷发的研究可以阐明[1]大量岩浆在上地壳堆积、储存、改造和喷发的过程；(2)侵入和喷出火成岩之间的关系；以及(3)深成岩和熔岩的构造。我们提出了一个多方面的方法来研究600千米3的桃泉凝灰岩(PST：中新世，亚利桑那州-加利福尼亚州-内华达州)的生成和喷发。广泛的流出表以及火山岩内凝灰岩和相关花岗岩的厚片的暴露使其成为一个特别吸引人的研究目标。PST斑晶组合包括一系列不同的副矿物，特别是丰富的辉石(钛铁矿)，它在记录演化条件和驱动微量元素变化方面发挥着至关重要的作用。需要解决的关键问题包括：[1]是什么环境因素控制了关键副矿物的赋存状态--尤其是辉石？[2]附件的生长如何影响岩浆的地球化学特征--这些特征如何被用来描述岩浆环境的演化？[3]在超级喷发之前，巨型洞穴中的条件是什么？[4]条件的波动有多大，它们是对补给、喷发还是大规模污染的直接反应？[5]大系统能持续多久，在它们生命的多少时间里，有一个巨大的岩浆室？[6]含有大量可喷发岩浆的岩浆室是天生不稳定的，还是触发抑制了异常长的时间，以允许大量岩浆积累？[7]如何以及如何有效地从富含晶体的残留物中提取大量富含熔融的岩浆？[8]高度演化的方式和地点，高硅流纹岩的产生？[9]长英质侵入岩和喷出岩之间的异同有什么意义？[10]为什么高度演化的深成岩的体积小于火山的等价物？[11]巨型喷发与其残余深成岩的等价物之间的关系是否与“正常”大小的喷发不同？他们的房间是大得多，还是他们更有效地提取可喷发的物质？这个项目将需要一种综合的、多学科的方法，涉及PI和具有不同专业知识和观点的合作者。该项目将结合广泛的野外工作、对岩石、玻璃、矿物和熔体包裹体样品的元素和同位素分析，使用几种互补的地质年代学方法进行测年，定量结构调查，以及旨在阐明辉石的稳定性和饱和行为的实验研究。在其他方法中，我们将使用高分辨率SIMS，CA-TIMS，LA-ICPMS，X射线断层成像以及CL和BSE，以及活塞筒和冷密封实验程序。广泛影响：该项目将为5名研究生(1名博士，4名MS)和7-8名本科生提供研究培训，从而在岩石学、地球化学和构造学方面发表可发表的贡献。这些学生中有很大一部分将是女性(也可能是少数族裔学生，特别是在圣何塞州立大学)。拟议的合作涉及私立和公立大学(Vanderbilt，SJSU)的初级和高级教员PI，以及与政府-大学合作伙伴关系(亚利桑那州地质调查局-UAZ；USGS-斯坦福；NM地质局-NM Tech)的合作者。其他不太正式的参与者包括来自广泛机构的本科生和研究生以及教职员工，他们将就需要解决的各种问题提供有价值的观点。科学成果将被纳入各自大学的教学模块。虽然这主要是一个基础科学项目，但其结果将涉及两个具有社会重要性的问题：可能导致灾难性喷发的巨型系统的行为，以及这些系统与主要金矿之间的可能关系

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual merit: "Super-eruptions" - explosive eruptions that produce 450 km3 of magma -arguably are the most catastrophic of all natural processes on Earth. They play a central role in ongoing debates about the nature of crustal magmatism. Study of super-eruptions may illuminate [1] the processes by which large quantities of magma accumulate in the upper crust, are stored and modified, and erupt; [2] the relations between intrusive and extrusive igneous rocks; and [3] the construction of plutons and batholiths. We propose a multi-faceted approach to investigate the generation and eruption of the 600 km3 Peach Spring Tuff (PST: Miocene, Arizona-California-Nevada). Exposure of the extensive outflow sheet as well as a thick intracaldera tuff section and related granite makes this a particularly appealing target for study. The PST phenocryst assemblage comprises a diverse array of accessory minerals, notably including abundant sphene (titanite), which plays a vital role in both recording evolving conditions and driving trace element variation. Critical questions to be addressed include: [1] What environmental factors control occurrence of key accessory minerals - especially sphene? [2] How does growth of accessories influence geochemical signatures of magmas - and how can these signatures be used to characterize evolution of magmatic environments? [3] What are the conditions in giant chambers immediately prior to super-eruptions? [4] How much do conditions fluctuate, and are they a direct response to replenishment, eruption, or wholesale contamination? [5] How long do large systems last, and during how much of their lifetime is there a large chamber? [6] Are chambers containing super-volumes of eruptible magma inherently unstable, or is triggering suppressed for unusual lengths of time to permit accumulation of enormous quantities of magma? [7] How, and how efficiently, are large volumes of melt-rich magma extracted from crystal-rich residue? [8] How and where are highly-evolved, high-silica rhyolites generated? [9] What is the significance of similarities and differences between felsic intrusive and extrusive rocks? [10] Why are highly evolved plutonic rocks less voluminous than volcanic equivalents? [11] Do giant eruptions have a different relation to their residual plutonic equivalents than 'normal'-sized eruptions? Are their chambers far larger, or do they more efficiently extract the eruptible material?This project will entail an integrated, multi-disciplinary approach involving PIs and collaborators with diverse expertise and perspectives. The project will combine extensive field work, elemental and isotopic analyses of rock, glass, mineral, and melt inclusion samples, dating using several complementary geochronological methods, quantitative textural investigations, and experimental studies aimed at elucidating the stability and saturation behavior of sphene. We will employ, among other methods, high-resolution SIMS, CA-TIMS, LA-ICPMS, imaging by X-ray tomography as well as CL and BSE, and piston cylinder and cold seal experimental procedures.Broader impacts: This project will provide research training for 5 graduate students (one PhD, 4 MS) and 7-8 undergraduate students leading to publishable contributions in petrology, geochemistry, and tectonics. A large proportion of these students will be female (and possibly minority students, especially at San Jose State). The proposed collaboration involves junior and senior faculty PIs at private and public universities (Vanderbilt, SJSU) and collaborators affiliated with government-university partnerships (AZ Geological Survey- UAZ; USGS-Stanford; NM Bureau of Geology-NM Tech). Other less formal participants include undergraduate and graduate students and faculty from a wide range of institutions who will provide valuable perspectives on the diverse problems that are to be addressed. Scientific results will be incorporated into teaching modules at the respective universities. Although this is principally a basic science project, the results will bear upon two issues of societal importance: behavior of giant systems that may produce catastrophic eruptions, and possible relationship between such systems and major gold deposits