203 Old and the New, Long and the Short: Perspectives on Integration of Timescales of Magmatic Processes: Special Session Related to MGPV Awards to Madison Myers and Anita Grunder

We encourage papers that challenge and give insights into the interplay between timescales, methodologies, and processes to build a cohesive understanding of the lifespan, evolution, storage, and eruption of magma, from plutonic to volcanic systems.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 216AB

Zircon petrochronology informs pre-eruptive magma evolution at Uturuncu volcano, Bolivian Andes

Paper number: 203-10
Program: Technical Sessions
Time: 4:00 PM – 4:15 PM

Authors

Abstract

The eruptive history of Cerro Uturuncu in the rear arc of the Central Volcanic Zone of the Andes spans over 1 m.y. defining six eruptive episodes. The main cone-building phase occurred between 595 and 220 ka, erupting at least 50 km3 of dacite lavas and domes. Activity has continued at Uturuncu through persistent degassing and uplift centered beneath the volcano, related to fluid exchange between the low-seismic velocity Altiplano-Puna Magma Body (APMB) and a shallow hydrothermal system. Despite several recent studies on the eruptive history, petrology, and magma plumbing system, many aspects of the shallow magmatic system's longevity and prevailing physicochemical conditions remain unanswered. Here, we present new zircon U-Pb crystallization ages and trace element contents from the youngest eruptive stage. Dominant zircon crystallization peaks occur between 500 and 600 ka, with lesser peaks of crystallization at 250–330 ka and 900–1100 ka. Individual lava weighted mean crystallization ages inferred from 40Ar/39Ar geochronology are c. 400 k.y. older than the eruption age. Hf contents and (Yb/Gd)N and Th/U ratios combined with individual zircon ages suggest significant overlap of magma storage with previous eruptions. Crystallization occurred within a restricted temperature range of 738°C to 768 °C, with a variation of ~20 °C. Zircon crystals erupted in Uturuncu lavas were largely derived from the developing steady-state magma system, representing a broadly cognate crystal cargo at the million-year scale. Most zircon rims record the recycling of material only a few hundred thousand years older than the eruption, whereas cores record longer timescales. Xenocrystic zircon inherited from pre-ignimbrites is rare, whereas Altiplano Puna Volcanic Complex ignimbrite age xenocrysts are more abundant, suggesting that the source of zircon crystallization is in the upper crust. In contrast, parental magmas ascended from a hotter, zircon-undersaturated source (the APMB). The protracted age span recorded by zircon crystallization ages in relation to the eruption ages indicates that thermomechanical conditions for zircon crystallization and saturation were maintained for several hundred thousand-year intervals. Together, these data suggest that individual eruptions within an eruptive stage exhibit continuous and overlapping crystallization histories. Zircon records storage at near-solidus to sub-solidus conditions after crystallization, with significant rim-to-core age variation, suggesting prolonged storage.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412337

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