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Genesis of adakite-like lavas of Licancabur volcano (Chile-Bolivia, Central Andes)

par Figueroa, Oscar;Déruelle, Bernard;Demaiffe, Daniel
Référence Comptes rendus. Géoscience, 341, 4, page (310-318)
Publication Publié, 2009-04

Article révisé par les pairs

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Résumé :

The Licancabur volcano is located on the Bolivia-Chile Altiplano (Central Andes). The lavas are andesites and dacites. Numerous mineralogic features attest that magma mixing occurred. Andesites have concave (spoon-shaped) REE patterns whereas dacites have steep slopes. A spectacular crossover of patterns occurs with increasing SiO2. Most geochemical discrimination criteria of adakites are satisfied by Licancabur dacites, except their high Sr-isotope compositions (> 0.7075). For the genesis of the Licancabur adakite-like lavas, a four-step model is proposed: (1) partial melting (5 to 10 wt %) of a subducted altered oceanic crust; (2) hybridation (< 10 wt %) of the magmas with melts derived from the overlying lithospheric mantle; (3) contamination (≈ 1 wt %) of these hybrid magmas by TTG-type granodiorites of the Archean lower continental crust (with present-day Sr-isotope ratios ≈ 0.820); (4) evolution and differentiation by crystal fractionation (< 6 wt %) and magma mixing at upper crustal levels. © 2008 Académie des sciences.