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Pressure-temperature-volatile contents variability of magmas feeding caldera-forming eruptions at Toba volcano

Wei-Ran Li 1, Marcus Phua1,2, Xiao-Yu Liu1, Francesca Forni3, Caroline Bouvet de Maisonneuve2, Hamdi Rifai4

  • Affiliations: 1VRock Laboratory, Department of Earth Sciences, The University of Hong Kong, Hong Kong; 2Earth Observatory of Singapore, Nanyang Technological University, Singapore; 3Dipartimento di Scienzedella Terra "A. Desio", Università degli Studi di Milano, Italy; 4Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Negeri Padang, Indonesia

  • Presentation type: Talk

  • Presentation time: Thursday 10:30 - 10:45, Room S150

  • Programme No: 1.1.7

  • Theme 1 > Session 1

Abstract

Toba volcano in Sumatra, Indonesia is known for four large caldera-forming eruptions in Quaternary, including the famous Youngest Toba Tuff (YTT) at ~74 ka and three older eruptions, namely HDT (~1.42 Ma), OTT (~784 ka), and MTT (~504 ka) that were less studied. Here we apply conventional and machine-learning based geothermobarometers and hygrometers to the four Toba tuffs, to determine the P-T conditions and volatile budgets of the sub-caldera magma. We found that the dacitic magma of the HDT had distinctly higher storage and pre-eruptive P-Ts, as well as lower H2O contents than the rhyolitic magmas of the later eruptions. Specifically, estimates for magma storage P-Ts from biotite-amphibole are similar for the OTT, MTT and YTT (T=770--825 °C; P=200--320 MPa and 100--200 MPa from biotite and amphibole respectively). Estimates of P-Ts from matrix glasses show two distinct populations for the HDT (median: 783 °C and 200 MPa, and 867 °C and 330 MPa) but single populations of lower values for the OTT, MTT and YTT (median: 750 ±20 °C and 120 ±30 MPa). Estimates for melt H2O contents from apatite show generally lower values for the HDT (mostly 3--5 wt%, indicating saturation P<140 MPa) than the OTT-MTT (mostly >5 wt%) and YTT (mostly >9 wt%, indicating saturation P>320 MPa). These indicate that the magma reached volatile saturation at different conditions before different eruptions, and the role that volatile saturation plays in eruption triggering may vary between caldera cycles.