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Low-pressure evolution of arc magmas in thickened crust: The San Pedro–Linzor volcanic chain, Central Andes, Northern Chile

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Year:
2014
Type of Publication:
Article
Keywords:
Low pressure magmatism
Authors:
Godoy, Benigno; Wörner, Gerhard; Kojima, Shoji; Aguilera, Felipe; Hartmann, Gerald
Journal:
Journal of South American Earth Sciences
Volume:
52
Pages:
24 - 42
ISSN:
0895-9811
BibTex:
Abstract:
Abstract Magmatism at Andean Central Volcanic Zone (CVZ), or Central Andes, is strongly influenced by differentiation and assimilation at high pressures that occurred at lower levels of the thick continental crust. This is typically shown by high light to heavy rare earth element ratios (LREE/HREE) of the erupted lavas at this volcanic zone. Increase of these ratios with time is interpreted as a change to magma evolution in the presence of garnet during evolution of Central Andes. Such geochemical signals could be introduced into the magmas be high-pressure fractionation with garnet on the liquidus and/or assimilation from crustal rocks with a garnet-bearing residue. However, lavas erupted at San Pedro–Linzor volcanic chain show no evidence of garnet fractionation in their trace element patterns. This volcanic chain is located in the active volcanic arc, between 22°00′S and 22°30′S, over a continental crust ∼70 km thick. Sampled lavas show Sr/Y and Sm/Yb ratios on, and contamination of mantle-derived magmas at the upper felsic crust (s related with the extensional regime that has existed in this zone of arc-front offset since Late-Miocene age, and the relatively thin portion of mafic lower crust observed below the volcanic chain.

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