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Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions.

ABSTRACT: The island of Bali in Indonesia is home to two active stratovolcanoes, Agung and Batur, but relatively little is known of their underlying magma plumbing systems. Here we define magma storage depths and isotopic evolution of the 1963 and 1974 eruptions using mineral-melt equilibrium thermobarometry and oxygen and helium isotopes in mineral separates. Olivine crystallised from a primitive magma and has average ?¹⁸O values of 4.8‰. Clinopyroxene records magma storage at the crust-mantle boundary, and displays mantle-like isotope values for Helium (8.62 R_A) and ?¹⁸O (5.0-5.8‰). Plagioclase reveals crystallisation in upper crustal storage reservoirs and shows ?¹⁸O values of 5.5-6.4‰. Our new thermobarometry and isotope data thus corroborate earlier seismic and InSAR studies that inferred upper crustal magma storage in the region. This type of multi-level plumbing architecture could drive replenishing magma to rapid volatile saturation, thus increasing the likelihood of explosive eruptions and the consequent hazard potential for the population of Bali.

SUBMITTER: Geiger H

PROVIDER: S-EPMC6043508 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions.

Geiger Harri H Troll Valentin R VR Jolis Ester M EM Deegan Frances M FM Harris Chris C Hilton David R DR Freda Carmela C

Scientific reports 20180712 1

The island of Bali in Indonesia is home to two active stratovolcanoes, Agung and Batur, but relatively little is known of their underlying magma plumbing systems. Here we define magma storage depths and isotopic evolution of the 1963 and 1974 eruptions using mineral-melt equilibrium thermobarometry and oxygen and helium isotopes in mineral separates. Olivine crystallised from a primitive magma and has average δ<sup>18</sup>O values of 4.8‰. Clinopyroxene records magma storage at the crust-mantle ...[more]

PMID: 30002471

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Project description:Crystal mush is rapidly emerging as a new paradigm for the evolution of igneous systems. Mid-ocean ridges provide a unique opportunity to study mush processes: geophysical data indicate that, even at the most magmatically robust fast-spreading ridges, the magma plumbing system typically comprises crystal mush. In this paper, we describe some of the consequences of crystal mush for the evolution of the mid-ocean ridge magmatic system. One of these is that melt migration by porous flow plays an important role, in addition to rapid, channelized flow. Facilitated by both buoyancy and (deformation-enhanced) compaction, porous flow leads to reactions between the mush and migrating melts. Reactions between melt and the surrounding crystal framework are also likely to occur upon emplacement of primitive melts into the mush. Furthermore, replenishment facilitates mixing between the replenishing melt and interstitial melts of the mush. Hence, crystal mushes facilitate reaction and mixing, which leads to significant homogenization, and which may account for the geochemical systematics of mid-ocean ridge basalt (MORB). A second consequence is cryptic fractionation. At mid-ocean ridges, a plagioclase framework may already have formed when clinopyroxene saturates. As a result, clinopyroxene phenocrysts are rare, despite the fact that the vast majority of MORB records clinopyroxene fractionation. Hence, melts extracted from crystal mush may show a cryptic fractionation signature. Another consequence of a mush-dominated plumbing system is that channelized flow of melts through the crystal mush leads to the occurrence of vertical magmatic fabrics in oceanic gabbros, as well as the entrainment of diverse populations of phenocrysts. Overall, we conclude that the occurrence of crystal mush has a number of fundamental implications for the behaviour and evolution of magmatic systems, and that mid-ocean ridges can serve as a useful template for trans-crustal mush columns elsewhere. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.

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Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions.

Publications

Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions.

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