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Holocene monogenetic silicic phreatomagmatic volcanism on the Altiplano of Bolivia: Cerro Volcán Quemado

Verenice Becerril-Gonzalez1, Shanaka de Silva1, Alejandro Cisneros de León1, Nestor Jimenez2, Frank Tepley1

  • Affiliations:  1College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis Oregon; 2Facultad de Ciencias Geológicas, Carrera de Geología, Universidad Mayor de San Andrés, La Paz, Bolivia

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 22

  • Programme No: 3.7.29

  • Theme 3 > Session 7

Abstract

The global record of significant volcanic eruptions is incomplete, limiting our understanding of volcanic history. One surprising unrecorded example is Cerro Volcán Quemado (CVQ), a rhyolitic monogenetic tuff cone-dome volcano located on the Altiplano behind the Central Volcanic Zone (CVZ) arc, a region dominated by effusive andesitic composite cones. Although CVQ is undated, its morphology suggests a Holocene age. Archeological evidence indicates that pre-Hispanic communities lived near CVQ but suddenly disappeared, raising the possibility that an eruption contributed to their disappearance. CVQ may hold critical insights into recent volcanic history and potential hazards in the Altiplano. CVQ's magmas are bimodal, with one extreme being rhyolite and the other being basaltic andesite, distinguishing it from the region's typical andesitic to dacitic compositions. Trachyandesites exhibit high Sr/Y ratios (84 to 90 ppm) indicating a deep crustal source, and amphibole thermobarometry indicates polybaric evolution in the mid-crust. In contrast, rhyolites have low Sr/Y values (13 to 20 ppm) indicating a shallow crustal source. CVQ's 206Pb/204Pb (~18.0) and 207Pb/204Pb (~15.6) isotopic signatures align with basement compositions indicating significant crustal contamination. 87Sr/86Sr isotopes (~ 0.706) show no correlation with differentiation. Our interpretation is the magma of CVQ originated in the deep crust through assimilation of the Arequipa-Barroso basement by mantle-derived basaltic magma and polybaric crystal fractionation produced trachyandesites and then rhyolites as the magmatic system traversed the crust. The phreatomagmatic character of the eruption connotes a recent wet period on the Altiplano.