CERRO VOLCÁN QUEMADO: AN ENIGMATIC HOLOCENE MONOGENETIC PHREATOMAGMATIC VOLCANO IN THE ALTIPLANO OF BOLIVIA

Understanding the history of Holocene volcanism is critical for determining likely hazards and risks to nearby societies. Even in remote populations, explosive eruptions can have far-flung effects due to ash transport and dispersal. Cerro Volcán Quemado, located in the Altiplano region of Bolivia, is a poorly documented volcano that contributes to the under-recorded number of global volcanic eruptions. Cerro Volcán Quemado is enigmatic because it is an explosive phreatomagmatic eruption that lies within an area dominated by effusive andesite volcanoes. The age of CVQ is unknown but observed fumarolic activity and modern morphology 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 Volcán 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. CVQ magmas indicate a bimodal magma composition ranging from rhyolite to basaltic andesite. 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 algorithm of Ridolfi and Renzuli (2012) 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. Our results will help improve the global volcanic database and the understanding of rhyolitic phreatomagmatic eruptions and their hazards.