Linking Modern, Rapid, Surface Uplift at the Laguna del Maule Volcanic Field, Chilean Andes, to Rhyolitic Magma-Driven Uplift Spanning the Holocene

Abstract:

The Laguna del Maule Volcanic Field includes an unusually large and recent concentration of silicic eruptions across a 23x17 km lake basin atop the southern Andes. We present findings that allow us to link currently observed deformation with a geological record of surface change spanning the Holocene. Since 2007 the crust here has been inflating at more than 20 cm/y. Geological, petrological, and geophysical findings have led to the hypothesis that the silicic vents have tapped an extensive, but ephemeral, layer of crystal-poor rhyolitic melt that began to form atop a mush zone that was established by ~20 ka, with a renewed phase of rhyolite eruptions concentrated around the southern flank of the basin during the Holocene (Singer et al., 2014). One of the earliest rhyolites, the 1 km³ Espejos coulée, ⁴⁰Ar/³⁹Ar-dated at 19 ka, dammed the northern outlet of Laguna del Maule raising the lake level ~200 m to form a prominent basin-wide shoreline. This shoreline was abandoned during an outbreak flood in the earliest Holocene. Surface exposure and ¹⁴C dating underway aims to refine the timing of the drop in lake level. Using an initial series of 40 short static GPS measurements around the basin, referenced to a set of 5 continuous GPS receivers, the elevation of this paleo-shoreline was determined to be 67 m higher at the southern end of the lake compared to the north. Interpretations of current surface deformation (Le Mével et al., in press), magnetotelluric data, earthquake distribution, and gravity changes suggest that magma is currently intruding at about 0.03 km³/yr at ~5 km depth. The amount of magma required to raise the surface 2 m during 8 yr is ~0.25 km³. If similar episodes of intrusion raised the roof of the magma reservoir by >60 m during the Holocene, it implies: (1) rapid accumulation of ~6 km³ of magma within the shallow crust, and (2) the locus of magma intrusion has shifted northward several km during the last 10 ky. It remains unclear whether any of the Holocene uplift was accommodated by faulting that may influence the distribution of silicic vents.

Le Mével, et al., Evolution of unrest at Laguna del Maule volcanic field (Chile) from InSAR and GPS measurements, 2003 to 2014. GRL, in press.

Singer, B.S., and 16 others (2014) Dynamics of a large, restless, rhyolitic magma system at Laguna del Maule, southern Andes, Chile. GSA Today 24, 4-10.