Collaborative Research: Examining the Temporal, Spatial and Geochemical Focusing of Magmatism During a Continental Arc Flare-up

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Continental margin volcanic arcs are locations of vast crustal growth factories, sites of extensive ore deposit formation and areas of widespread mountain building. They are also locations of dangerous volcanic eruptions that can disrupt the lives of millions of people at any time and over large regions. Although a basic understanding of volcanic eruptions exists, the different behaviors of eruption such as location, volumes and frequency are not well understood. Part of the problem is that volcanoes are only the surface expression of the complex physical and chemical processes that occur below the Earth's surface in vertically extensive magma plumbing systems that feed the volcanoes. One important but poorly understood type of volcanic behavior is the spatial and temporal focusing of these systems best documented in volcanic fields, as expressed through the change from initially low volume, compositionally heterogeneous and spatially spread-out volcanism to high volume, homogeneous and spatially focused volcanism often leading to large volcanic eruptions. If magma focusing begins at deeper crustal levels, what processes control this phenomenon, and how does it manifest itself in style, location, volume, and the frequency of volcanic eruptions? To answer this, it is essential that we understand the mechanisms by which magmatism is focused during vertical transport through the crustal column and how volcanic and deeper magmatic systems are linked to one another. Understanding the processes causing magma focusing will also help us understand ore deposit formation and aspects of mountain building and the growth of continents. Preliminary research in the central Sierra Nevada, California, has led to three important discoveries: (1) a clear pattern of spatiotemporal and geochemical magmatic focusing in a field of Cretaceous plutons with the large 95 to 85 Ma Tuolumne Intrusive Complex (TIC), in Yosemite National Park occurring at the center of the focus; (2) a number of host rock pendants in this area preserve volcanic rocks that mimic the same temporal and geochemical focusing as the plutons; (3) a number of subvolcanic porphyry "volcanic feeder systems" occur in this area, linking volcanic and plutonic fields of the same age. These discoveries provide the opportunity to investigate the potential causes and processes facilitating magma focusing in the mid-upper crust that leads to the generation of focused volcanic systems, like those established in the San Juan volcanic field in Colorado or the Aucanquilcha volcanic cluster in Chile. The proposed study will examine two scales: 1) Studying the broad spatiotemporal geochemical pattern of volcanic and plutonic units at the peripheral boundaries of a large silicic pluton; 2) Targeting key plutonic-porphyry feeder-volcanic "triads" to examine volcanic-plutonic links during the focusing. The proposed research will use field mapping, geochemical analyses and geochronology to explore spatial/temporal/compositional focusing of magmatism at 6-11 km depths in an ancient arc, and compare to similar phenomena established in modern volcanic systems. This project supports two early career women, PhD student Ardill at USC and assistant professor Memeti at CSU Fullerton, and professor Paterson from USC. Several undergraduates and one graduate student from Hispanic-Serving CSU Fullerton will be involved. A free mobile application will be developed in collaboration with CSU Fullerton assistant professor Dr. Natalie Bursztyn that will enhance student learning in the geosciences and engage the general public by taking them on a virtual field trip back in time through the Sierra Nevada magmatic arc. The project emphasizes training in analytical methods at home and at collaborating facilities. Paterson and Memeti will continue a 12 yr collaboration with Yosemite National Park.