Cerro Volcán Quemado: An Enigmatic Holocene Monogenetic Phreatomagmatic Volcano in the Altiplano of Bolivia

Cerro Volcán Quemado (CVQ) is a rhyolitic tuff cone-dome complex consisting of five craters in the Altiplano of Bolivia. Cerro Quemado is unique in composition when compared to the surrounding andesitic volcanoes in the region. The age of CVQ is unknown, but observed fumarolic activity and regional climate history suggest a late Pleistocene to Holocene age. This enigmatic volcano contains critical knowledge of recent volcanic history and potential hazards of the Altiplano region. We initiated the first comprehensive study of the enigmatic volcano to determine the age and origin of this volcano. The rhyolitic composition of CVQ raises questions about the origin of the magma and the development of a significant phreatomagmatic center. In this contribution, we report the first petrological data on Cerro Quemado.

The CVQ lithologies are predominantly variably vesicular, banded rhyolite with volumetrically insignificant but ubiquitous andesitic enclaves. Rhyolites are crystal-poor rocks (4-5%) with phenocrysts of plagioclase, K-feldspar, biotite, rare hornblende, and accessory zircon, apatite, and oxide. Plagioclase compositions in rhyolitic pumices range from oligoclase to andesine. Plagioclase compositions in basaltic andesite scoria predominantly fall between bytownite to labradorite, with a few analyses in the andesine field. Preliminary P-T estimates based on amphibole compositions, using the Ridolfi and Renzuli (2012) algorithm, indicate temperatures between 967 - 1037 °C and pressures of equilibration between 13 - 30 km depth.

Data suggest an upper crustal rhyolitic magma was recharged by andesitic magma initiating ascent that culminated in the interaction with surface water to trigger an extensive episodic phreatomagmatic eruption.