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Magmatic timescales prior to the 2014-15 eruption at Fogo, Cape Verde: Insights from diffusion chronometry of olivines and clinopyroxenes

Ross Hassard1, Hilary Downes1 Eleanor Jennings1 Simon Day2

  • Affiliations: 1School of Natural Sciences, Birkbeck University of London, Malet Street, London WC1E 7HX, UK  2Institute for Risk and Disaster Reduction, University College London, Gower Street, London, WC1E 7HX, UK.

  • Presentation type: Poster

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

  • Poster Board Number: 275

  • Programme No: 1.3.19

  • Theme 1 > Session 3

Abstract

Historical records from Fogo island (Cape Verde) reveal significant impacts of eruptions on the local population, including loss of livestock, destruction of buildings and farming areas and, occasionally, death of inhabitants. The limited volcano monitoring network and the lack of diffusion chronometry studies means there are significant gaps in our understanding of the timescales of magmatic processes at this active volcano. This research aims to enable better eruption forecasting and hazard mitigation at Fogo by using diffusion chronometry data from clinopyroxene and olivine phenocrysts in lava flows from the most recent eruption in 2014/15, to improve understanding of pre-eruption, magmatic timescales. Key research objectives are (i) to determine diffusion timescales from normally-zoned clinopyroxene and olivine crystals to understand magma and/or lava flow residence times and ascent rates; (ii) to determine whether there a link between seismicity and eruptions at Fogo through the comparison of diffusion timescales with recorded seismic activity. Initial findings include an assessment of diffusion chronometry methods which shows that published Fe-Mg diffusion coefficients underestimate timescales in Al-rich clinopyroxenes, such as those at Fogo. Initial results using published Mg self-diffusion coefficients, indicate clinopyroxene bands from the 2014-15 eruption formed ~305 days prior to eruption (based on 4 samples) and rims formed ~157 days prior to eruption (based on 14 samples). Diffusion chronometry from 16 olivine phenocrysts reveals timescales of hours in the lava flow for proximal samples, and up to 5 weeks for distal samples.