Integrating Geomorphology, Geochronology, and Numerical Modeling of 60 Meter Surface Inflation to Reveal Holocene Growth of the Silicic Magma Reservoir Beneath Laguna del Maule, Chile
Monday, 8 January 2018: 12:10
Salon Quinamavida (Hotel Quinamavida)
Bradley S Singer1, Hélène Le Mével2, Joseph M Licciardi3, Loreto Cordova4, Nicolas Garibaldi1, Angela K. Diefenbach5, Nathan L Andersen6 and Kurt L Feigl7, (1)University of Wisconsin Madison, Madison, WI, United States, (2)Carnegie Institution for Science, Washington, DC, United States, (3)University of New Hampshire Main Campus, Durham, NH, United States, (4)Observatorio Volcanológico de los Andes del Sur (OVDAS), Servicio Nacional de Geología y Minería (SERNAGEOMIN), Temuco, Chile, (5)USGS, Cascades Volcano Observatory, Vancouver, WA, United States, (6)Georgia Institute of Technology Main Campus, Atlanta, GA, United States, (7)University of Wisconsin, Madison, WI, United States
Abstract:
Laguna del Maule (LdM) Volcanic Field comprises a large concentration of silicic eruptions surrounding a 23x17 km lake basin atop the Andes. Since 2007 the crust has been inflating at >20 cm/y. Geology, petrology, and geophysics suggest that eruptions have tapped an extensive, but ephemeral, layer of rhyolitic melt that began to form atop a mush zone by ~20 ka, with a renewed phase of eruptions concentrated around the southern flank of the basin during the last 14.5 ka. The Espejos coulée,
40Ar/
39Ar-dated at 19.0±0.7 ka, dammed the northern outlet of LdM and raised its level ~200 m to form a prominent basin-wide shoreline. Subsidiary shorelines up to 15 m lower than the highstand are less well preserved.
36Cl measurements of wave-cut Pleistocene rhyodacite and andesite, where multiple shoreline horizons are visible between 2376 and 2386 masl, yield ages of 9.4±0.2, 8.8±0.3, 7.5±0.2, 6.6±0.3, and 4.2±0.1 ka. We infer an initial drop in lake level at 9.4 ka, and that the younger dates record later positions of lower shorelines, or erosion. This interpretation is bolstered by a
36Cl age of 8.4±0.6 ka from a lava flow that erupted onto the highstand shoreline.
GPS positions of 65 sites on the highstand surface measured with cm-scale precision (rapid-static mode), augmented by a photgrammetrically-generated 1 m resolution DEM, reveal a 62 m elevation difference between the SE and NW highstand surface. The elevation gradient and spatial distribution are consistent with an inflating magma source located SE of the lake, but may include minor displacement on faults. To investigate the origin of the deformed shoreline, we use analytical and numerical models of repeated magma injections into a long-lived reservoir and calculate the resulting surface displacement over 9.4 ka. Assuming the vertical displacement reflects intrusions of magma corresponding to episodes of non-eruptive inflation, similar to unrest of the past decade, we can quantify the total volume of magma feeding the system during the Holocene. Modeling the geomorphic signal offers a rare opportunity to provide the ratio of intrusion to eruption in a silicic system by comparing simulated magma recharge volumes to the erupted volume of rhyolite. Moreover, the growth rate of the reservoir can be constrained over a time period well beyond the short historical record of unrest.
