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Understanding the crustal pathway of magmas in the Auckland Volcanic Field

Joshua Coker 1, Elaine Smid2, Lucy McGee1, Eduardo Morgado3

  • Affiliations: 1Department of Earth Sciences, University of Adelaide, Adelaide, Australia; 2School of Environment, University of Auckland, Auckland, New Zealand; 3Escuela de Geología, Universidad Mayor, Santiago, Chile

  • Presentation type: Poster

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

  • Poster Board Number: 66

  • Programme No: 1.2.11

  • Theme 1 > Session 2

Abstract

With its last eruption c. 550 years BP, the Auckland Volcanic Field (AVF), New Zealand, is still regarded as an active monogenetic field beneath a population of approximately 1.7 million people.  Using the textures and mineral compositions of primarily olivine and clinopyroxene phenocrysts across 7 of the 53 volcanic centres, the aim is to provide insights into subsurface dynamics. Current theories propose magmas are not significantly affected by assimilation or extensive crystallisation, as suggested by their chemical compositions including Mg# as high as 70 - indicative of a primitive and relatively uninhibited source to surface journey for the melt. Textures such as diffuse normal and oscillatory zoning within olivine, oscillatory zoning in clinopyroxene and exsolution in oxide phases, however, indicate complexity in the crustal plumbing system which can be interpreted using mineral specific tools.  Targeting Fe-Mg diffusion within tephra-derived olivine phenocrysts, the modelling software DIFFSIM is used to determine diffusion timescales as a proxy for ascent rates within AVF, with preliminary results on the scale of days to months. Input parameter constraints such as temperature and oxygen fugacity are determined in conjunction with reverse thermodynamic models produced with easyMelts software. Understanding the dynamics of the magma's ascent from source to surface, to a degree whereby a model of plumbing can be suggested, is an important component to understanding the dynamics and potential hazards of future eruptions.