21 Frontiers in Geochronology: Advances and Applications in the Geosciences

This session highlights cutting-edge geochronologic advances and applications that illuminate Earth’s dynamic history. We welcome contributions spanning new analytical techniques, integrative studies, and innovative case examples demonstrating the essential role of time in geosciences.

Tuesday, 10 March 2026
10:00 AM - 12:00 PM
RCC, 104

Magmatic Evolution of Água de Pau Volcano: Insights from Zircon Geochemistry and U–Th Geochronology

Paper number: 21-1
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Abstract

The magma mush dynamic model remains a subject of interest as volcanologists strive to understand the magmatic processes that affect silicic magma reservoirs. Silicic magmatic systems are well known for their catastrophic impact on the environment during eruptions. These systems provide insight into magmatic and volcanic processes beneath their calderas. The Fogo volcano (Água de Pau) on São Miguel Island ejects plutonic (syenite) clasts and volcanic rocks, which offer valuable insights into the mechanisms that drive magma eruptions. However, the genetic relationship between these plutonic clasts and the associated volcanic products remains poorly constrained, and geochronological data on the syenite are limited.

In this study, we investigate the relationship between the plutonic rocks observed as syenite clasts and their associated volcanic rocks by integrating U-Th geochronology and zircon trace element geochemistry on syenite clasts and pumices from the Fogo “A” together with pumice samples from Fogo B, Ribeira Chã, and Pisão eruption units. Zircon crystallization ages and geochemistry were obtained using the Sensitive High-Resolution Ion Microprobe with Reverse Geometry (SHRIMP-RG) and the Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), respectively, on syenite clasts and pumice from each unit. The weighted mean zircon crystallization ages from syenites are 13.78±0.52 ka, 16.97±0.57 ka, 21.3±1.1 ka, and 24.6±1.4 ka.

These ages postdate their associated pumice deposit from the “Fogo A” unit, which yields a mean weighted crystallization age of 50±3.5 ka, indicating that the syenites are not related to the volcanic rocks through fractional crystallization but rather crystallized within an evolving magma reservoir and were entrained during the Fogo “A” eruption. Zircons from syenite xenoliths and Fogo “A” pumices exhibit similar rare earth element (REE) patterns and overlapping Hf concentrations and Zr/Hf ratios. These signatures suggest that zircons from both samples crystallized from a chemically similar source. Zircons from the syenites overlap the Eu/Eu values of the Pisão unit, indicating that the syenites represent remnants of earlier magmatic formations undergoing continued evolution. Zircon ages and trace elements reveal a complex magmatic system beneath Água de Pau. These findings provide insights into the conditions of magma storage beneath the Fogo volcano.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411595

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