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Understanding resurgence and restlessness at calderas: insights from climatic vs post-climatic eruptive compositions with particular reference to Toba, Sumatra Public Deposited

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  • Although calderas and the caldera cycle are well studied, the relationship between caldera-forming eruptions and post-caldera volcanism is poorly understood. The chemical characteristics of the erupted products suggest that two end member compositions are involved during resurgence: (1) remnant magma of similar composition to the magma of the climactic eruption; and (2) a more mafic magma. Remnant magma may motivate uplift due to recovery of isostatic, lithostatic, and magmastatic equilibrium after the climactic eruption, or be rejuvenated by recharge magma. Often a mixing trend suggests mixing between the end members. Resurgence at Toba Caldera, Indonesia, involves significant structural uplift with associated volcanism (in and around the caldera) since the caldera-forming eruption 74 ka. The Samosir lava domes, on the eastern flank of the resurgent dome, compositionally overlap with the Youngest Toba Tuff (YTT; 70-75% SiO2) suggesting remobilization and eruption of the remnant YTT magma. In the north, the Sipisupisu lava dome represent the most mafic post-collapse volcanism around the caldera (52-60% SiO2) while the Pardepur lava domes in the south show compositions between Sipisupisu and the YTT (65-67% SiO2), suggesting they might represent more hybrid compositions of remnant YTT and recharge magma. Age and spatial relations suggests in the Toba system, the signal of recharge is muted in the central part within the caldera where mainly remobilized remnant magma erupted. On the periphery, the signal of mafic recharge is much stronger maybe suggesting less remnant magma. 35 km north of Toba is an actively erupting volcano, Sinabung, that has strong isotopic and age links to Toba Caldera. Sinabung lavas overlap with Toba’s compositions but are proportionally more towards the mafic end member (55-60% SiO2). Sinabung may therefore be part of Toba’s post-caldera history but located outside the magmatic shadow zone and tapping the recharge magma in the resurgent Toba system. The silicic, remnant YTT magma is centered under the Samosir domes, while the mafic recharge signal gets stronger further away from the center of the caldera.
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  • Bowers, J., de Silva, S., Mucek, A., Pratomo, I., and Putra, A., 2017, Understanding the resurgence and restlessness at calderas: insights from climatic and post-climatic eruptive compositions with particular reference to Toba Caldera, IAVCEI Scientific Assembly, Abstract MT23B-024.
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  • Portland, Oregon
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