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Pre-eruptive magmatic processes leading to the Puig Jordà monogenetic eruption (Garrotxa Volcanic Field, Spain)

Helena Albert 1, 2, Louise Muir1, Dario Pedrazzi3, Guillem Gisbert1, 2, Xavier Bolós3, Adelina Geyer3, Meritxell Aulinas1,2

  • Affiliations:  1Department of Mineralogy, Petrology and Applied Geology, University of Barcelona, Marti Franques s/n, 08028, Barcelona, Spain; 2Geomodels Research Institute, Universitat de Barcelona, 08028, Barcelona, Spain; 3Geosciences Barcelona (GEO3BCN), CSIC, Lluís Solé Sabarís s/n, 08028 Barcelona, Spain

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 251

  • Programme No: 1.1.37

  • Theme 1 > Session 1

Abstract

Petrological studies of monogenetic eruptions have proven that magmas do not always ascend directly from the mantle but instead involve processes like magma mixing or assimilation of crustal material. This challenges traditional views, especially in regions like the Garrotxa Volcanic Field (GVF), where past eruptions were believed to result from direct magma ascent, supported by the presence of mantle xenoliths in some volcanoes. To explore this hypothesis in the GVF, we conducted a petrological study of the Puig Jordà monogenetic volcano. Our investigation focuses on olivine, clinopyroxene and spinel crystals, revealing evidence of magma arrest and mixing processes prior to eruption. Thermobarometric modelling suggests rapid magma ascent from a deep zone at ca. 1000-1100 MPa and 1200-1240°C, followed by the incorporation of previously emplaced magma batches located at 500-900 MPa and 1140-1190°C, and a final stage occurring at shallow crustal levels with lower temperatures (ca. 1110°C). Our new findings indicate that shallow and transient magma reservoirs exist in the GVF, and have significant implications for the duration of pre-eruptive unrest in the GVF and, hence, for the interpretation of monitoring data in the future. Furthermore, our study has revealed that either the traditionally associated Bosc de Tosca lava flow is not sourced from this volcano, or that the eruption involved the emission of two distinct magmas, leading to the formation of pyroclastic deposits and the lavas. This work was financed by the grant PID2023-151693NA-I00 (funded by MCIN/AEI/10.13039/501100011033) and by the Parc Natural de la Zona Volcànica de La Garrotxa.