Pre-eruptive magmatic processes associated with the historical (218 +/- 14 aBP) explosive eruption of Tutupaca volcano (southern Peru)

Co-auteur étranger; International audience; Magma recharge into a differentiated reservoir is one of the main triggering mechanisms for explosive eruptions. Here wedescribe the petrology of the eruptive products of the last explosive eruption of Tutupaca volcano (southern Peru) in order toconstrain the pre-eruptive physical conditions (P-T-XH2O) of the Tutupaca dacitic reservoir. We demonstrate that prior to theparoxysm, magma in the Tutupaca dacitic reservoir was at low temperature and high viscosity (735 ± 23 °C), with a mineralassemblage of plagioclase, low-Al amphibole, biotite, titanite, and Fe-Ti oxides, located at 8.8 ± 1.6 km depth (233 ± 43 MPa).The phenocrysts of the Tutupaca dacites show frequent disequilibrium textures such as reverse zonation, resorption zones, andovergrowth rims. These disequilibrium textures suggest a heating process induced by the recharge of a hotter magma into thedacitic reservoir. As a result, high-Al amphibole and relatively high-Ca plagioclase phenocryst rims and microlites were formedand record high temperatures from just before the eruption (840 ± 45 °C). Based on these data, we propose that the recent eruptionof Tutupaca was triggered by the recharge of a hotter magma into a highly crystallized dacitic magma reservoir. As a result, theresident dacitic magma was reheated and remobilized by a self-mixing process. These magmatic processes induced an enhancedphase of dome growth that provoked destabilization of the NE flank, producing a debris avalanche and its accompanyingpyroclastic density currents.