Estudio petrográfico de los depósitos volcánicos del volcán Quilotoa :Caracterización geoquímica y petrográfica de dos columnas estratigráficas del volcán Quilotoa.

Abstract

The Quilotoa volcano is a potentially active volcano located in central Ecuador, which has experienced at least eight eruptions of moderate to large size (VEI 4-6) every 10-15 thousand years. Despite its high explosivity and recurrence of eruptions, this volcano lacks a detailed description of its volcanic deposits. Through the study of two stratigraphic sections, this work aims to improve knowledge about the past eruptions of this volcano, conducting field observations, descriptions of thin sections, and geochemical analyses. Five stratigraphic units possibly formed in the last 14,700 years were recognized, separated by four paleosols. All units consist of more than one type of deposit (fallout, pyroclastic flow, or surge) of similar composition and mineralogy, generally containing dense juvenile lithics and pumice. A detailed study of mineral components shows that the content of hornblende and biotite decreases, and the content of plagioclase increases (<7% vol.) from the oldest to the most recent units. These mineral changes are accompanied by a slight rise in Al2O3 in the most recent units. The main differences found between the units are the modal percentage of minerals and the texture of the matrix present in the rock samples; these changes are attributed to the variation in the dissolved water content in the melt and not to changes in the chemical composition of the magma. Conducting detailed studies of volcanic deposits from past eruptions contributes as a basis for analyzing the evolution, styles, and eruptive dynamics of potentially active volcanoes in Ecuador.