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

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"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 ofmagma -arguably are the most catastrophic of all natural processes on Earth. They playa central role in ongoing debates about the nature of crustal magmatism. Study ofsuper-eruptions may illuminate [1] the processes by which large quantities of magmaaccumulate in the upper crust, are stored and modified, and erupt; [2] the relationsbetween intrusive and extrusive igneous rocks; and [3] the construction of plutons andbatholiths. We propose a multi-faceted approach to investigate the generation anderuption of the 600 km3 Peach Spring Tuff (PST: Miocene,Arizona-California-Nevada). Exposure of the extensive outflow sheet as well as a thickintracaldera tuff section and related granite makes this a particularly appealing target forstudy. The PST phenocryst assemblage comprises a diverse array of accessoryminerals, notably including abundant sphene (titanite), which plays a vital role in bothrecording evolving conditions and driving trace element variation. Critical questions tobe addressed include: [1] What environmental factors control occurrence of keyaccessory minerals - especially sphene? [2] How does growth of accessories influencegeochemical signatures of magmas - and how can these signatures be used tocharacterize evolution of magmatic environments? [3] What are the conditions in giantchambers 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 alarge chamber? [6] Are chambers containing super-volumes of eruptible magmainherently unstable, or is triggering suppressed for unusual lengths of time to permitaccumulation of enormous quantities of magma? [7] How, and how efficiently, are largevolumes of melt-rich magma extracted from crystal-rich residue? [8] How and where arehighly-evolved, high-silica rhyolites generated? [9] What is the significance of similaritiesand differences between felsic intrusive and extrusive rocks? [10] Why are highlyevolved plutonic rocks less voluminous than volcanic equivalents? [11] Do gianteruptions have a different relation to their residual plutonic equivalents than'normal'-sized eruptions? Are their chambers far larger, or do they more efficientlyextract the eruptible material?This project will entail an integrated, multi-disciplinary approach involving PIs andcollaborators with diverse expertise and perspectives. The project will combineextensive field work, elemental and isotopic analyses of rock, glass, mineral, and meltinclusion samples, dating using several complementary geochronological methods,quantitative textural investigations, and experimental studies aimed at elucidating thestability and saturation behavior of sphene. We will employ, among other methods,NATIONAL SCIENCE FOUNDATIONProposal AbstractProposal:0911726 PI Name:Miller, CalvinPrinted from