Work

Does pre-ascent magma storage influence eruption style? An evaluation from textures and geochemistry of phenocrysts at Taranaki volcano

Year: 2025

Type: article

Abstract: Understanding the explosivity of future volcanic eruptions is a cornerstone of hazard evaluation, and magma storage days to years leading up to eruption could provide timely information for mitigation strategies. To explore the influence of pre-ascent conditions on eruption style we compared the growth histories of plagioclase and amphiboles phenocrysts from four prominent, Holocene-aged, explosive erupted deposits with six effusive eruptions at Taranaki volcano, New Zealand. The explosively erupted andesite-dacite magmas display a range of bulk compositions and crystallinities that overlap with those erupted effusively. Regardless of their eruption style, each phenocryst population displays a high degree inter-crystal textural, geochemical and Sr-isotope discordance, including in their final rim growth. This can be explained by the periodic intrusive disruption of a redeveloping crystal mush that lacked a unidirectional assimilation-fractional-crystallisation path in the centuries to millennia between eruptions. However, amphiboles from most of the effusive eruptions are distinguished from those erupted explosively by recording late-stage halogen (and likely other volatiles) accumulation in the magma and subsequent decomposition during slow ascent. Also more prevalent in the effusive eruptions are plagioclase textures that record late-stage mingling with a mafic melt. These features support conceptual models that suggest magma compressibility due to volatile accumulation allows more efficient magma mingling during recharge and thus heating. The resulting melt viscosity reduction and enhanced outgassing of the magma then promotes effusive eruption. Testing this hypothesis via mineralogical determination of intensive parameters would need to overcome the high degree of disequilibrium that occurred at all stages of the magma evolution.

Source: Journal of Volcanology and Geothermal Research

DOI: 10.1016/j.jvolgeores.2025.108502

Authors: Phil Shane, Shanice Mascarenhas, Teresa Ubide, Shane J. Cronin

Institutions: University of Auckland, The University of Queensland

Language: English

Topic: Geological and Geochemical Analysis

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $3,420

Funders: University of Auckland, Ministry of Business, Innovation and Employment