Multiple, Coeval Silicic Magma Storage Domains Beneath the Laguna Del Maule Volcanic Field Inferred From Gravity Investigations

Abstract

The rhyolite‐producing Laguna del Maule volcanic field (LdMVF), Chile, has had numerous post‐glacial eruptions that produced large explosions and voluminous lava flows. During the Holocene ∼60 m of surface uplift is recorded by paleo‐shorelines of the fresh‐water Laguna del Maule, with an inflation source near the Barrancas volcanic complex. Rhyolites from the Barrancas complex erupted over ∼14 ka including some of the youngest (1.4 ± 0.6 ka) lava flows in the field. New gravity data collected on the Barrancas complex reveals a residual gravity low (−6 mGal, “Barrancas anomaly”) that is distinct from the pronounced gravity low (−19 mGal; “Lake anomaly”) associated with present‐day ground uplift to the northwest. Three‐dimensional inversion of the Barrancas anomaly indicates the presence of a magma body with a maximum density contrast with the host rock of −250 kg/m3 centered at a depth of ∼3 km below surface. Nearby Miocene high‐silica granites represent frozen remnants of highly evolved rhyolitic magma. Comparison of the densities measured from samples of these plutons with the geophysical model densities, and integration of thermodynamic modeling of silicic melt evolution, provide constraints on our interpretation. We propose a magma body, containing <30% melt phase and low volatile content, exists beneath Barrancas. The Barrancas and Lake gravity lows represent magma in different physical states, associated with past and present‐day storage beneath LdMVF. The gravity model mirrors geochemical observations which independently indicate that at least two distinct rhyolites were generated and stored as discrete magma bodies within the broader LdMVF.

A free-geometry geodynamic modelling of surface gravity changes using Growth-dg software

“…Since 2007, widespread deformation 38 , 39 at rates greater than 20 cm/year 40 have been observed and modelled by an inflating sill 41 , 42 at about 3 km below sea level (5 km below surface). The field is characterized by a 19 mGal Bouguer gravity low, centred over the deformation source, caused by a shallow, crystal-poor, volatile-rich, silicic magma system overlying the sill 43 , 44 .

Figure 6 Location of LdMvf.

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The integrated history of repeated caldera formation and infill at the Okataina Volcanic Centre: Insights from 3D gravity and magnetic models

“…Their model suggests a depth to basement of around 3 (±0.5) km within the caldera. Seebeck et al (2010) concluded that a magma body at 6 km depth beneath the OVC was likely undetectable, however the assumption of a rhyolitic magma body having a density contrast of only − 0.300 g/cm 3 (2.470 g/cm 3 absolute) likely significantly underestimates the density contrast of magma found at similar silicic centers, that may be up to 0.7 g/cm 3 (absolute 1.9 g/cm 3 ) when the magmatic volatile phase is taken into account (e.g Miller et al, 2017;Trevino et al, 2021).…”

Dissecting a Zombie: Joint Analysis of Density and Resistivity Models Reveals Shallow Structure and Possible Sulfide Deposition at Uturuncu Volcano, Bolivia

“…While gravity modeling is mathematically non-unique (LaFehr and Nabighian, 2012), at Uturuncu we have a wealth of geophysical (Jay et al, 2012;Ward et al, 2014;Comeau et al, 2016;Kukarina et al, 2017;Hudson et al, 2021) and petrological (Sparks et al, 2008;Muir et al, 2014b;Muir et al, 2014a;Muir et al, 2015) information to constrain our modeling. When used in conjunction with other data sets, gravity measurements can be a powerful tool for understanding complex volcanic structures (Trevino et al, 2021), highlighting features other methods may be blind to. A density model of the upper 10 km at Uturuncu of comparable resolution to the existing resistivity model could falsify or support the presence of saline fluids at Uturuncu and their contribution to the deformation signal.…”

“…However, these three scenarios would have quite different densities, with the potential to falsify any one of these hypotheses. Gravity surveys have imaged subsurface density structure at multiple volcanic systems (Zurek and Williams-Jones, 2013;Young et al, 2020;Trevino et al, 2021). A gravity inversion by del Potro et al (2013) revealed a ca 15 km wide low density column rising from the APMB beneath Uturuncu, but this model lacks sufficient resolution to compare with the low resistivity anomalies Comeau et al (2016) imaged in the upper 10 km.…”