RECONSTRUCCIÓN GEOLÓGICA DEL VOLCÁN CHULLCANI (MIOCENO SUPERIOR A PLIOCENO SUPERIOR): CONSIDERACIONES GENERALES SOBRE GEOQUÍMICA Y EDAD DE LAS FASES VOLCÁNICAS, ANDES CENTRALES DE BOLIVIA

Abstract

The Chullcani volcano is located at Northern of Bolivian Cordillera, between Oruro and La Paz, at about 4, 600 m about ocean level. According to the SiO2 vs, alkalis diagrams, the studied rocks may be defined as acid to intermediate, and the K2O vs. SiO2 discrimination diagram indicates that Chullcani rocks belong to the K-rich calcoalkaline magmatic series. The samples that fall in the field of the trachydacite, correspond to the domes Jitiri and León Iquiña, the lavas fall in the field of the trachyandesites and the estratovolcano Chullcani, unit Wuichukollu and unit Carbon Kollu, the rest of the samples fall in the field of the rhyolites that correspond to the tuffs and the dome Yapukkollu. The diagrams of discrimination of the magmatic series allow us to determine that the rocks involved in the study area have character subalcaline and they belong to the series calcoalkaline rich in potassium. The geology evolution of this volcano developed in two period of time. In the Late Miocene: the magmatic activity started with the extrusion of the Yapukkollu dome and Khalani tuff. At about 6.13±0.120 Ma was deposited the lavas and tuffs, and followed by the formation the Jitiri and León Iquiña Domes at 6.2±0.4 Ma. Early Pliocene: In this period of time the magmatic activity in the Bolivian Cordillera was characterized by the deposition of the ignimbrite beds (Pérez Formation) at about 2.3±0.2 Ma followed by igneous activity comprised of the Wuichukkollu lavas and Ventilla tuffs, volcanic breccias (diatremas), and finished with the Carbon Kollu Meseta and Pucara domes formation trapping actual magmatic activities.