Magnetotelluric images of magma distribution beneath Volcán Uturuncu, Bolivia: Implications for magma dynamics

Comeau, Matthew J.; Unsworth, Martyn; Ticona, Faustino; Sunagua, M.

doi:10.1130/g36258.1

Cited by 125 publications

(133 citation statements)

References 27 publications

Supporting

Mentioning

123

Contrasting

Order By: Relevance

“…They show that the high electrical conductivity (~1 S m -1 ) of the APMB, while maintaining the low melt fractions defined seismically (Ward et al, 2014), can be matched by andesitic melts with high water contents (7-10 wt%). Note that an alternative scenario, wherein the APMB contains dacite melt containing the observed dissolved water content of ≤4 wt%, cannot explain the high electrical conductivity of the APMB as imaged by Comeau et al (2015). To do so, a substantially higher (by at least a factor of 1.5) melt fraction compared to the seismically constrained fraction would be needed (Ward et al, 2014).…”

Section: Petrologymentioning

confidence: 99%

“…Andesitic and basaltic andesitic enclaves in Uturuncu lavas and in silicic ignimbrites of the APVC (Michelfelder et al, 2014) are interpreted as aliquots of the least evolved resident magmas in the APMB entrained into the volumetrically dominant, silica-rich dacite magmas (Sparks et al, 2008). The mafic magmas have less radiogenic strontium and more radiogenic neodymium isotopes than associated dacites (Michelfelder et al, 2014) and are thought to be Size and geometry of anomalous structures Schilling et al (2006); Comeau et al (2015Comeau et al ( , 2016 Gravimetry A pproximately 12-24 km wide, vertically elongated (8-12 km high), low-density structures rooted at the top of the APMB at ~15 km below sea level Surface velocity and spatiotemporal evolution of deformation Fialko and Pearse (2012); Henderson and Pritchard (2013);del Potro et al (2013a); Blewitt et al (2016) Geomorphology Absence of sustained residual long-term deformation Null result for residual ground deformation at time, t > 100 yr Perkins et al (2016) Note: See text for details on numerical model. APMB-Altiplano-Puna magma body.…”

Section: Petrologymentioning

confidence: 99%

See 1 more Smart Citation

Thermomechanical modeling of the Altiplano-Puna deformation anomaly: Multiparameter insights into magma mush reorganization

et al. 2017

View full text Add to dashboard Cite

A 150-km-wide ground deformation anomaly in the Altiplano-Puna volcanic complex (APVC) of the Central Andes, with uplift centered on Uturuncu volcano and peripheral subsidence, alludes to complex subsurface stress changes. In particular, the role of a large, geophysically anomalous and partially molten reservoir (the Altiplano-Puna magma body, APMB), located ~20 km beneath the deforming surface, is still poorly understood. To explain the observed spatiotemporal ground deformation pattern, we integrate geophysical and petrological data and develop a numerical model that accounts for a mechanically heterogeneous and viscoelastic crust. Best-fit models imply subsurface stress changes due to the episodic reorganization of an interconnected vertically extended mid-crustal plumbing system composed of the APMB and a domed bulge and column structure. Measured gravity-height gradient data point toward low-density fluid migration as the dominant process behind these stress changes. We calculate a mean annual flux of ~2 × 10 7 m 3 of water-rich andesitic melt and/or magmatic water from the APMB into the bulge and column structure accompanied by modest pressure changes of <0.006 MPa/yr. Two configurations of the column fit the observations equally well: (1) a magmatic (igneous mush) column that extends to a depth of 6 km below sea level and contains trapped volatiles, or (2) a volatile-bearing hybrid column composed of an igneous mush below a solidified and permeable body that extends to sea level. Volatile loss from the bulge and column structure reverses the deformation, and explains the absence of broad (tens of kilometers) and long-term (>100 yr) residual deformation at Uturuncu. Episodic mush reorganization may be a ubiquitous characteristic of the magmatic evolution of the APVC.

show abstract

Section: Petrologymentioning

confidence: 99%

Section: Petrologymentioning

confidence: 99%

Thermomechanical modeling of the Altiplano-Puna deformation anomaly: Multiparameter insights into magma mush reorganization

et al. 2017

View full text Add to dashboard Cite

show abstract

“…It is of enormous dimensions and has recently been detected further south as well (Comeau et al 2013). All geophysical data hint at widespread melting, including a low-velocity zone as inferred from seismic tomography (Heit et al 2008).…”

Section: Altiplanomentioning

confidence: 99%

Three-dimensional inversion of magnetotelluric data from the Central Andean continental margin

2014

View full text Add to dashboard Cite

Magnetotelluric data were collected in the late 1990s in the Central Andes of Chile and Bolivia, with the aim to delineate the electrical conductivity distribution in the subsurface and its relations to subduction processes. In previous studies, these data were interpreted based on 2-D models. The principal result was a vast conductivity zone beneath the Altiplano high plateau at mid and lower crustal depths and a much smaller, though significant conductor associated with the Precordillera Fault System. However, there are some significant 3-D effects in the investigation area, in particular near the coast and on the eastern Altiplano. The aim of this work is to give a reinterpretation based on new 3-D inversion of these data. The 3-D inversion not only provides a better fit to the data compared to 2-D results but furthermore allows to include sites with strong telluric distortion which were ignored in previous studies. We are now able to explain anomalous phases above 90°and induction arrows pointing subparallel to the coast as observed at several sites in the Coastal Cordillera. These strongly distorted data are caused by highly conductive near-surface structures that are partly connected to the Pacific Ocean, forcing currents to flow around the sites. The lower crust beneath the Coastal Cordillera resembles a poorly conductive, nearly homogeneous half-space and is electrically unremarkable. Besides, we can now image the Precordillera conductor as a continuous, elongated feature. The volcanic arc of the Western Cordillera is highly resistive with the exception of a few conductive spots which may be associated with certain individual volcanoes or geothermal resources, respectively. The Altiplano conductor is again the dominant electrical feature in the Central Andes, indicating widespread melting of the middle and lower back-arc crust.

show abstract

“…However, 2 Ma ago the volcanic activity decreased in magnitude and the eruptive style shifted to smaller and more effusive eruptions (e.g., De Silva and Gosnold, 2007;Salisbury et al, 2011). At a much larger, whole crustal scale, the APVC structure has been studied from a geophysical point of view by seismic tomography and receiver functions (e.g., Chmielowski et al, 1999;Zandt et al, 2003;Ward et al, 2014), electromagnetic methods (Schilling et al, 2006;Comeau et al, 2015), and gravity (e.g., Götze and Krause, 2002;Tassara et al, 2006;Riller et al, 2006;Del Potro et al, 2013). These studies show either the possible presence of magma body about 17 km below the surface (APMB, Altiplano Puna Magma Body) and an upper crust of felsic composition.…”

Section: Geological Frameworkmentioning

confidence: 99%

Nuevos antecedentes sobre la estructura interna de la caldera La Pacana mediante un estudio gravimétrico (Andes centrales, Chile).

Delgado

Pavez

2015

Andgeo

View full text Add to dashboard Cite

ABSTRACT. La Pacana (central Andes, Northern Chile) is one of the largest resurgent calderas in the world, formed 4 Ma ago during an eruption with a VEI of 8.7. We undertake a gravimetric study to contribute new insights into the inner structure and evolution of this caldera. The La Pacana Bouguer residual anomaly is asymmetric and has an average amplitude of -12 to -14 mGal, which we interpret as being produced by the low-density intracaldera ignimbrite infill. A reinterpretation of the caldera stratigraphy plus the available geochronology suggests that the current shape of La Pacana was produced by the collapse of two nested calderas, roughly limited by the axis where the resurgent dome changes its orientation, with the oldest eruption in the southern part of La Pacana. The gravity data suggests that these southern and northern nested structures would have collapsed with downsag and trap-door geometries respectively, evidence of asymmetric subsidence. Intra caldera ignimbrite thicknesses were calculated with 2.5D forward models and show that the ignimbrite infill in its southern and northern parts reach ∼0.6-1.1 km and ∼2.5-3 km respectively. Using Gauss's theorem, we calculate the volume of the intra caldera ignimbrite infill is ∼3,400-3,500 km 3 , in agreement with previous estimates and with models that show that the larger the caldera diameter, the larger the erupted volume.Keywords: La Pacana caldera, Volcanology, Gravimetry, Caldera collapse.RESUMEN. Nuevos antecedentes sobre la estructura interna de la caldera La Pacana mediante un estudio gravimétrico (Andes centrales, Chile). La Pacana (Andes centrales, norte de Chile) es una de las calderas resurgentes más grandes del mundo, formada 4 Ma atrás en una erupción con un VEI de 8,7. Hemos realizado un estudio gravimétrico de la caldera para contribuir con nuevos antecedentes sobre su estructura interna y evolución. La anomalía residual de Bouguer de La Pacana es asimétrica y tiene una amplitud promedio de entre -12 a -14 mGal, la que se interpreta que es producida por el relleno de baja densidad de ignimbritas intracaldera. Una reinterpretación de la estratigrafía de la caldera junto con la geocronología disponible sugiere que la forma actual de La Pacana fue producida por el colapso de dos calderas anidadas, cuyo límite aproximado sería el eje donde el domo resurgente cambia su orientación, y con la erupción más antigua en la parte sur de La Pacana. Los datos gravimétricos sugieren que estas estructuras anidadas sur y norte habrían colapsado con geometrías de tipo downsag y trap-door respectivamente, evidencias de subsidencia asimétrica. Los espesores de las ignimbritas intracaldera fueron calculados con modelos directos en 2.5D los cuales muestran que el relleno en sus partes sur y norte alcanza a los ∼0,6-1,1 km y ∼2,5-3 km respectivamente. Mediante el teorema de Gauss, calculamos que el volumen de las ignimbritas intracaldera llega a los ∼3.400-3.500 km 3 , de acuerdo con estimaciones previas y con modelos que muestran que mientras más grande es el di...

show abstract

Magnetotelluric images of magma distribution beneath Volcán Uturuncu, Bolivia: Implications for magma dynamics

Cited by 125 publications

References 27 publications

Thermomechanical modeling of the Altiplano-Puna deformation anomaly: Multiparameter insights into magma mush reorganization

Thermomechanical modeling of the Altiplano-Puna deformation anomaly: Multiparameter insights into magma mush reorganization

Three-dimensional inversion of magnetotelluric data from the Central Andean continental margin

Nuevos antecedentes sobre la estructura interna de la caldera La Pacana mediante un estudio gravimétrico (Andes centrales, Chile).

Contact Info

Product

Resources

About