EAGER: Investigating the possibility of low temperature (<700 C) melt in silicic igneous systems

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The questions of how Earth's crust was made by silicic magmas, and how large volcanoes like Yellowstone erupt, have perplexed geologists for centuries. This project will include collecting new geochemical data from observed volcanic rocks and performing laboratory experiments aimed at assessing the controversial hypothesis that magmas at temperatures of 500 to 550 degrees C play a role in making and erupting silicic melts. The project has potential to make transformative change on views of how silicic magma systems operate with potential impacts including how the continental crust forms, why silicic magmas erupt, and how ore deposits form. This project will train a graduate student, and develop a new device for thermal gradients in a cold seal system that will benefit other experimental petrologists. This exploratory project builds upon the recent finding that hydrous peralkaline melts can coexist with quartz + feldspar at temperatures below the nominal igneous solidus (700 degrees C). Three tasks aimed at assessing the possibility that this low temperature melt exists and plays a role in eruption of silicic magmas are proposed: 1) Assess the role of decompression of low temperature melt in equilibrium with quartz and feldspar by releasing pressure from 1 kb to 0.3 kb and comparing to know phase equilibria; 2) Develop a thermal gradient apparatus using cold seal vessels at 1 kb pressure; 3) Compare the intra mineral isotope ratios of U, Fe and Si from mineral separates of the Fish Canyon Tuff to assess if connections between the making of granites and silicic volcanic rocks can be discerned.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.