LATE-STAGE MAGMATIC EVOLUTION ON ISLA GUADALUPE, MEXICO: PRESSURE- AND WATER CONDITIONS OF POST-SHIELD DIFFERENTIATION
Isla Guadalupe is an oceanic volcanic island in the Pacific Ocean 300 km west of Baja California (Mexico), located along the fossil Guadalupe spreading centre. Recent volcanic activity has generated a variety of eruptive products including lava domes, scoria cones, and lava flows reflecting a range of compositions from basalt to trachyte. Batiza (1977a) identified fractional crystallization as the main process controlling magma evolution, occurring at 0.2–1 GPa under relatively hydrated conditions. This study constrains pressure, temperature, and magmatic water contents using XRF major element data, petrography, and modeling with the Magma Chamber Simulator (MCS). Results show that the magma source for dikes formed at ~1 GPa (35 km depth), 1218–922 °C, and <2 wt% H₂O; the magma source for domes crystallized at ~0.8 GPa (28 km), 1196–746 °C, with similar water-contents. Despite limitations in predicting hydrous mineral stability, rhyolite-MELTS version 1.2.0 constrains on temperature, pressure, and water contents. For the first time, the Magma Chamber Simulator (MCS) modern modelling program in combination with the MELTS engine was implemented to provide new insights into the magma differentiation, thereby enhancing detail for crystallisation-depth estimated of the late-stage volcanic sequences on Isla Guadalupe. Therefore, this research enables a more detailed and previously unresolved reconstruction of the late-stage magmatic evolution of Isla Guadalupe.