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| Titel |
Deep structure beneath Uturuncu volcano in the central Andes: Insights from new density anomaly models |
| VerfasserIn |
Rodrigo del Potro, Joachim Gottsmann, Antonio Camacho, Mayel Sunagua |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053276
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| Zusammenfassung |
| Volcanic activity in the central Andes during the Quaternaty has evolved from very large
silicic volcanic centres that generated huge volumes of ignimbrites to, more recently, the
eruption of silicic lavas that built large composite cones. The deep structures of these volcanic
systems can be broadly inferred from a density anomaly inversion model. As part of an
integrated multidisciplinary investigation of the on-going uplift of Uturuncu volcano in
southern Bolivia, we are interested in understanding the constraints of sub-surface
architecture and regional structures on the spatio-temporal variations in geophysical
parameters during the emplacement and evolution of the active mid-crustal intrusion. Herein,
we present a density anomaly 3D inversion model of an area of 5000 km2 around Uturuncu.
This survey saw the combined use of spring gravimeters and dual frequency GPS
receivers, at 143 new static stations with average station spacing of about 5 km.
Gravity data uncertainty is below 100 μGal for individual benchmarks and GPS data
uncertainty is below 6 cm in the vertical. At the scale of the current survey, these
settings allow for a precise determination of the anomalous gravimetric signature.
Alongside the static gravity survey, six free air gradients and a microgravity survey
have been carried out in the area. Static gravity data are employed to construct a
detailed Bouguer anomaly map and, from it, a 3D model of the subsurface density
distribution. The inversion routine builds a subsurface model defined by the 3D
aggregation of parallelepiped cells, based on a controlled ’growth’ process of anomalous
density bodies (with a density contrast of ± 150 kg m-3) by means of an exploratory
approach. The regional gravity trend is calculated as part of the inversion routine
and for this 60 regional data points are added. A new visualising tool allows us to
generate 3D images of the density anomalies and hence better understand their
geometries and relation to surface manifestations of volcanism. Our results show that
Uturuncu and other neighbouring volcanoes are centred over a bowl-shaped low density
body that extends to, at least, 15 km depth, where the 70 km-wide footprint of the
current deformation anomaly constrains the source of the deformation, a region that
other regional geophysical data indicate is the top of a thick region of hot partially
molten rock. Strong negative anomalies root up towards the volcanic centres and
smaller bodies are in some cases clearly related to hydrothermal systems with surface
manifestations. One deep and large negative anomaly corresponds to the location
of the large Vilama caldera system. Smaller and superficial positive and negative
density bodies are aligned in N-S trends, in agreement with regional tectonic features. |
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