RHEOLOGIC CONSTRAINTS OF THE CARBONAL DACITE, GUANACASTE, COSTA RICA

The Carbonal dacite is a thick and expansive lava flow in the Guanacaste province of northwest Costa Rica. The large spatial extent of the Carbonal dacite (it is found in locales roughly 80 km apart) is problematic considering the high viscosity of dacitic lavas. This problem is the focus of an ongoing research project that seeks to develop a rheologic model for the Carbonal dacite that will clarify its extent and means of emplacement. The rheologic model will be based on geothermobarometric and other geochemical analyses and address the following questions: 1) under what temperature and pressure conditions was the Carbonal dacite erupted and crystallized, 2) what was the flow viscosity of the Carbonal flow, and 3) how does the calculated flow viscosity inform the spatial extent of the flow? In addition to the immediate scope of the project, the model could provide further insight into the generation of new continental crust, as the silicic lava flows and ignimbrites of northwest Costa Rica are integral in understanding the creation of silicic magmas from mafic sources in oceanic subduction environments.