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Homogeneous mush and sub-solidus carapace feed post-caldera volcanism within the Toba Caldera

Alejandro Cisneros de León1 , Shanaka L. De Silva1, Axel K. Schmitt2, Martin Danišík2, Adonara Mucek1, Jade Bowers1, Tushar Mittal3, Indio Patromo4

  • Affiliations:  1College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, USA; 2John de Laeter Centre, Curtin University, Australia; 3Department of Geosciences, Pennsylvania State University, University Park, PA, USA; 4 Geological Agency, Jl. Diponegoro No. 57, Bandung, Java Barat, Indonesia. 

  • Presentation type: Poster

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

  • Poster Board Number: 279

  • Programme No: 1.3.22

  • Theme 1 > Session 3

Abstract

Among the uncertainties surrounding the dynamics of post-caldera magma systems, quantitative constraints on the spatiotemporal evolution of resurgent magmatic reservoirs and their connections to surface expressions remain poorly understood. The Toba caldera in Sumatra, the site of the largest supereruption in the last 2 Myr (Youngest Toba Tuff, YTT; ~75 ka), underwent magmatic resurgence shortly after the eruption, progressing from intra-caldera to extra-caldera locations. Previous studies suggest multiple sub-reservoirs contributed to the YTT supereruption and we test whether this is recorded in the nature, genetic relationships, and evolution of magmas feeding post-supereruption domes. This study combines zircon thermochronology ([U-Th]/He dating) and petrochronology (crystallization ages, trace elements, and oxygen isotopes) to investigate intra-caldera domes on Samosir Island, a crystal-rich enclave within one dome, and extra-caldera domes/volcanoes (e.g., Sipisupisu, Pardepur, Pusuk Buhit, and Sinabung). Zircon thermochronology from the central Samosir domes confirms post-YTT extrusion ages of ~64--68 ka. Petrochronological data reveal a magmatic history spanning 500 kyr, mirroring YTT magmas, with no evidence for heterogeneity within the footprint of the caldera. However, extra-caldera centers reveal heterogeneity. Zircon ages from the crystal-rich enclave cluster around 100 ka, contrasting with the host dome's inherited protracted crystallization history. These findings suggest post-supereruption domes were sourced from partially solidified remnants of YTT magmas that potentially originated from mush remobilization at ~100 ka. This study offers critical insights into pre- and post-caldera magmatic evolution and resurgence, advancing our understanding of some of the Earth's largest and most dynamic volcanic systems.