Pre-eruptive conditions of basaltic andesite at Arenal Volcano, Costa Rica

• Applicant: Dr. Fleurice Parat
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2008 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 108815160

Arenal volcano is currently one of the only arc volcanoes undergoing multi-decade activity. The bulk composition of magma erupted has remained nearly constant during almost 40 years of continuous activity. However, minerals and melt inclusions record a complex open-system evolution in which steady state production of the erupted basaltic andesitic magma is linked to episodic injections of basalt into Arenal magma reservoir system. The monotony of erupting Arenal magmas implies that fractionation, recharge, ascent, and eruption are well balanced in order for magmas to be essentially uniform while containing phenocrysts with different growth histories at the time of eruption. In this project, high-temperature and high-pressure experiments will be conducted to determine the pre-eruptive conditions of basaltic andesitic magmas erupted at Arenal volcano. We planed to investigate the influence of temperature (900-1100°C), pressure (200- 400 MPa), water activity (XH2O=0.3-1), and oxygen fugacity on phase equilibria, mineral and melt proportion and composition. The results will constrain the storage of mafic magma at depth, the presence and exsolution of the fluid phase, the processes evolved during differentiation to more felsic magma and the crystallization of mafic mineral in both basaltic and dacitic magmas (e.g. An-rich plagioclase). The production of a near steady-state whole rock composition over decadal time scales will be discussed as well as the production of earlier dacitic tephras and the changes from explosive or effusive eruption with compositionally similar mafic magmas during the last 40 years. The results are also of general interest for the production of high-alumina basalts and basaltic andesites in arcrelated volcano and for the questions about magmatic reservoir dynamics, petrogenetic history, and eruptive style of volcanic eruption.

• DFG Programme: Research Grants