Expanding Geophysical and Geochemical Investigation of Causes of Extraordinary Unrest at the Laguna del Maule (Rhyolitic) Volcanic Field, Southern Andes, Chile

Abstract:

The Laguna del Maule Volcanic Field, Chile, includes an unusually large and recent concentration of silicic eruptions. Since 2007 the crust here has been inflating at an astonishing rate of 25 cm/yr. Findings thus far lead to the hypothesis that the silicic vents have tapped an extensive layer of crystal-poor, rhyolitic melt that began to form atop a magmatic mush zone that was established by ~20 ka with a renewed phase of rhyolite eruptions during the Holocene. Modeling of surface deformation, magnetotelluric data, and gravity changes suggest that magma is currently intruding at a depth of ~5 km. Swarms of volcano-tectonic and long period earthquakes, mostly of M < 2, have occurred beneath the most recent rhyolite coulees on the southwestern and southern margins of the 20 km diameter ring of silicic vents.

With support from the US NSF and the Chilean government (SERNAGEOMIN and OVDAS) we are seizing the unique opportunity to investigate, over the next 5 years, the dynamics of this large rhyolitic system while magma migration, reservoir growth, and crustal deformation are actively underway. This collaboration involves scientists and students at: University of Wisconsin-Madison, Georgia Tech, Cornell, University of Alberta, Simon Fraser University, University of Chile-Santiago, CONICET/University of San Juan-Argentina, Nanyang Technological University-Singapore, SERNAGEOMIN, OVDAS, USGS, and SEGEMAR-Argentina. Team members will be introduced in this presentation.

Our approach includes augmenting the OVDAS array of 6 permanent seisic stations with 40 additional instruments to conduct tomographic, receiver function and ambient noise studies. We continue to collect 4-D gravity data from 37 stations. Surface deformation is monitored via cGPS at 5 permanent receivers and InSAR data. A magnetotelluric survey across the Andes at 36o S is planned. Geochemical studies include mineral zoning and U-Th disequilibrium of zircons to constrain the timing of magma intrusion and mixing events prior to the current unrest. The overall aim is to integrate these observations and to construct numerical models of system dynamics. We are developing communications protocols and a web site to facilitate sharing of findings among the team members and with the public.