Consideraciones petrológicas de los estratovolcanes de Costa Rica

Abstract

The geotectonic conditions, the processes of fractional crystallízation, the variations in the parcial mailing conditions and source compositions, and to a cer tain extent, the assimilation of continental crust and magma mixture, control the-magma formation and the chemical caracterization of volcanic rocks of Costa Rica. It is supposed that there exist two different parental magmas. The Guanacaste Volcanic Chain and Central Volcanic Chain are typically subalkaline rocks. The petrografic analysis indicate a great similarity between the calcalkaline lavas of the Rincon de la Vieja and Miravalles volcanoes, and between the Barva, Irazú and Turrialba volcanoes, respectively. The rocks of Poas and Platanar volcanoes show a olear tendency towards the tholeitic series, while same samples of Congo, Hule, Arenal and Chato are transitional to both series, andesites to high alumina basalticandesites. The presence of casual hornblende in high calcalumina and low potassium basalticandesites can be usad in the evaluation of volcanic hazard.