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Evidences of crustal contamination and magma mixing at Taapaca Volcanic Complex, Central Andes

AuthorsPolanco, E.; Clavero, J.; Gimeno, D.; Fernandez-Turiel, J. L. CSIC ORCID
Issue DateJun-2009
CitationGeochimica et Cosmochimica Acta 73(13) Supl 1: A1037 (2009)
AbstractTaapaca Volcanic Complex (TVC: 18°06 S, 69°30 W and 5,850 m a.s.l., Late Pliocene to Holocene) is an active eruptive center of ca. 35 km3 that is located in the Central Andes in the Altiplano of northern Chile. TVC is mainly composed by lavas, domes, block-and-ash flow, blasts and debris avalanche deposits. Clavero et al. [1] indicate that the volcanic activity (stages I to IV) is characterized by 4-5 km SW vent migration and short cycles of intrusion and extrusion dacitic domes associated with block-and-ash flows and blasts and several sector collapses; followed by long periods of quiescence. Its products are mainly dacitic in composition, as most of the volcanoes of the Central Andes [2], with ubiquitous mafic inclusions and characteristic sanidine megacrysts. The samples collected and analysed (whole-rock, minerals and isotope geochemistry) correspond to high-K (2.6-3.5%, m/m) calc-alkaline dacites and subordinated andesites, tipical of subduction settings [2]. The data have high incompatible mobil elements (Sr and Ba: 715-1059 and 791-1707 µg/g) and show Nb anomaly. Also, REE patterns have LREE very enriched and relative low Pb isotopic composition, indicating that the crustal contamination and assimilation processes are important in the evolution of the TVC magmas, consistent with the >70 km crustal thickness of this segment of the Andes. In addition, the Nd and Sr ratios are identical to values of other volcanoes of this volcanic zone [2]. However, the mafic inclusions, the reabsortion textures (mainly in plagioclase and quartz) and oscillatory zoned plagioclases are evidences of the ocurrence of magma mixing processes where pulses of new less evolved (and hot) magma input into the shallower magmatic chamber of TVC. Probably, the later process triggered the successive eruptive cycles.
Description1 página.-- Resumen del trabajo presentado en la 19th Annual V.M. Goldschmidt Conference, V.M. Goldschmidt Conference.
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