DECIPHERING THE HISTORY OF TENORIO VOLCANO, COSTA RICA: A COMPREHENSIVE GEOCHEMICAL AND GEOCHRONOLOGICAL STUDY OF A DORMANT VOLCANO

The volcanic activity of Tenorio volcano in Costa Rica's Cordillera de Guanacaste has remained largely enigmatic due to dense vegetation, impeding detailed studies on its explosivity and associated hazards. This study looks into Tenorio’s potential for renewed activity and documents Tenorio's volcanic history through geochemical, petrographic, and geochronological data. Approximately sixty lava flow and tephra samples were collected, and a preliminary geologic map was created. These samples were used to establish temporal relationships among rock units, finalize the geologic map, and decipher Tenorio's magmatic evolution. The mystery of Tenorio's volcanism, including its eruptive cycles and potential activity, was previously unexplored. Local oral histories and geological evidence suggest precolonial volcanic activity, and seismic clusters recorded in 1998, 2002, and 2018 indicating possible unrest. This study integrates existing knowledge with well-sampled stratigraphy to illuminate Tenorio's eruptive history and assess volcanic hazards. Collaboration with the Costa Rican Emergency Commission (CNE) and the Costa Rica National Park Service (SINAC) has enriched this project. The study's outcomes will be shared with these institutions, enhancing local science education and understanding of active volcanism. We analyzed lava flow samples for lithologic and mineral variations and conducted XRF and ICP-MS analyses. Key units in the stratigraphic column were dated using ⁴⁰Ar/³⁹Ar dating. Coupling whole-rock chemistry with geochronological data provided temporal constraints for the geologic units indicated in the geologic map. The resulting data allowed the construction of a detailed stratigraphic sequence and geological map, offering insights into Tenorio's magmatic history and aiding in accurate volcanic hazard assessment. Preliminary findings suggest that Tenorio Volcano effusive volcanism is voluminous during the Middle Pleistocene (0.5 to 0.2 Ma), and its geochemistry points out the importance of decompression crystallization significantly influencing Tenorio's magma variation, impacting the crystallization sequence and assemblage. This study advances our understanding of Tenorio’s volcanic dynamics and exemplifies collaborative international geoscience research.