Geological, petrological and geochemical framework of Miravalles-Guayabo caldera and related lavas, NW Costa Rica

Thermobarometric estimates suggest that basaltic and magmas equilibrated with their phenocrystic phases at 1080-1120 °C, and pressures ranges of 380-430 MPa, whereas andesitic melts are confined at 200-230 MPa and temperatures of 1050-1070 °C. In turn, amphibole-biotite dacites equilibrated at 240-290 MPa and temperatures of 920-950 °C approaching water saturated conditions (with H2O contents up to 5.7-7.2 wt%). Thermobarometry indicate that contiguous andesitic-dacitic magma lenses are stored within the subvolcanic region at depths below 10 km, whereas basaltic magmas are stored and degas at slightly higher depths (up to ~15 km). Single eruptions associated with the emplacement of lava flows seem to be related to the tapping of portions of single magma lenses during minor unrest episodes. Conversely, caldera forming eruptions involved the ejection of differentiated rhyolitic pumices (of La Ese member) and likely occurred during recharge and pressurization of this heterogeneous reservoir under critical stress conditions.