T232 The Life and Times of Arc Volcanoes from Bottom to Top II

Wednesday, 13 October 2021
1:30 PM - 5:30 PM
A106

INTEGRATING PETROLOGIC AND GEOPHYSICAL PERSPECTIVES ON THE RHYOLITIC MAGMA RESERVOIR AT LAGUNA DEL MAULE, CHILE

Paper number: T232-16
Program: Technical Sessions
Time: 5:10 PM – 5:30 PM

Authors

Abstract

The Laguna del Maule volcanic field (LdM), central Chile, is among the premier natural laboratories for interdisciplinary investigations of silicic magmatism. Between the last glacial maximum and <2000 years ago, LdM produced >20 explosive and effusive rhyolite eruptions. Since 2007, uplift centered in the ring of rhyolite-producing vents has been sustained at >200 mm/y.

Rhyolite at LdM is generated within a trans-crustal magma system by fractional crystallization and assimilation of juvenile crust. Compositional contrasts between early post-glacial and Holocene rhyolites indicate they were sourced from distinct reservoirs at similar shallow depths. Zircon ages show these reservoirs coexisted for >100 ky, during which time crystals cycled between high- and low-temperature growth. Models of Mg diffusion in plagioclase from Holocene rhyolite suggests mobile magma was extracted from the reservoir only decades prior to eruption; yet there are no signs of pre-eruptive reheating despite ample evidence for the shallow intrusion of mafic magma. Instead, stalled mafic magma contributed CO2-rich fluid to the overlying rhyolite, potentially catalyzing crystallization, volatile exsolution, and eruption.

Gravity, seismic, and MT imaging at LdM identify a several-hundred km3, largely crystal-rich magma reservoir at 2-10 km depth. The complimentary sensitivities of these methods reveal a more detailed structure including crystal-poor magma and fluid associated with the inflation center and melt-rich lenses distributed throughout the shallow system.

Recent discussions of the duration of mobile magma storage and eruption triggering have contributed to a “warm vs cold” storage framework. That most tomographic studies fail to locate melt-rich bodies is often cited to support “cold” storage. While the LdM magma system is dominantly crystal-rich, the brief storage recorded by plagioclase alongside the long, temperature-variable zircon growth history indicates a temporally and spatially variable thermal regime, that retained mobile rhyolite throughout post-glacial time, obviating a dichotomous “warm vs cold” framework. Moreover, the geophysical results at LdM demonstrate that melt concentrations unresolved by individual methods can be revealed through a multi-disciplinary approach.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-367555

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