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

San Jose State University Foundation, San Jose CA

Investigators

Abstract

"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, NATIONAL SCIENCE FOUNDATION Proposal Abstract Proposal:0911726 PI Name:Miller, Calvin Printed from