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Partial Melting in the Central Andean Crust: a Review of Geophysical, Petrophysical, and Petrologic Evidence

Authors

Schilling,  F. R.
External Organizations;

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Trumbull,  Robert
4.2 Inorganic and Isotope Geochemistry, 4.0 Chemistry and Material Cycles, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Brasse,  H.
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Haberland,  Christian
2.2 Geophysical Deep Sounding, 2.0 Physics of the Earth, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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Asch,  Günter
2.4 Seismology, 2.0 Physics of the Earth, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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Bruhn,  David
4.1 Reservoir Technologies, 4.0 Chemistry and Material Cycles, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Mai,  K.
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Haak,  V.
External Organizations;

Giese,  P.
External Organizations;

Muñoz,  M.
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Kummerow [Ramelow],  Juliane
Deutsches GeoForschungsZentrum;

Rietbrock,  A.
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Ricaldi,  E.
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Vietor,  T.
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Citation

Schilling, F. R., Trumbull, R., Brasse, H., Haberland, C., Asch, G., Bruhn, D., Mai, K., Haak, V., Giese, P., Muñoz, M., Kummerow [Ramelow], J., Rietbrock, A., Ricaldi, E., Vietor, T. (2006): Partial Melting in the Central Andean Crust: a Review of Geophysical, Petrophysical, and Petrologic Evidence. - In: Oncken, O., Chong, G., Franz, G., Giese, P., Götze, H.-J., Ramos, V. A., Strecker, M. R., Wigger, P. (Eds.), The Andes - Active Subduction Orogeny, (Frontiers in Earth Sciences), Springer, 459-474.


https://gfzpublic.gfz-potsdam.de/pubman/item/item_234676
Abstract
The thickened crust of the Central Andes is characterized by several first-order geophysical anomalies that seem to reflect the presence of partial melts. Magnetotelluric and geomagnetic deep-sounding studies in Northern Chile have revealed a high conductivity zone (HCZ) beneath the Altiplano Plateau and the Western Cordillera, which is extreme both in terms of its size and integrated conductivity of > 20 000 Siemens. Furthermore, this region is characterized by an extremely high seismic attenuation and reduced seismic velocity. The interrelation between the different petrophysical observations, in combination with petrological and heat-flow density studies, strongly indicates a huge area of partially molten rocks that is possibly topped with a thin, saline fluid film. The average melt fraction is deduced to be ~20 vol.%, which agrees with typical values deduced from eroded migmatites. Based on the distribution and geochemical composition of Pliocene to Quaternary silicic ignimbrites in this area, this zone is thought to be dominated by crustally-derived rhyodacite melts with minor andesitic contribution. An interconnected melt distribution – typical for migmatites – would satisfy both the magnetotelluric and seismic observations. The high melt fraction in this mid-crustal zone should lead to strong weakening, which may be a main cause for the development of the flat topography of the Altiplano Plateau.