4:00 PM - 4:15 PM
[SGC35-09] Investigating shallow submarine eruption processes recorded in dissolved H2O contents of marine tephra: example of Oomurodashi volcano tephra in drill core C9010E
Keywords:FTIR spectroscopy, H2O speciation, Submarine eruptions, Tephra
H2O is dissolved in melts and glasses as two species, molecular H2O and OH, which can be measured using Fourier Transform Infra Red spectroscopy (FTIR). Low temperature secondary hydration increases H2Om but does not alter OH. Using imaging FTIR analyses and a species-dependent H2Ot molar absorptivity coefficient (McIntosh et al 2017 Am. Mineral.) to overcome analytical issues relating to thin glasses, it is now possible to accurately measure OH concentrations and thus to investigate volcanic processes even in glasses affected by secondary hydration.
We present here an example of silicic tephra contained in the marine sedimentary core C9010E drilled by the D/V Chikyu in 2009 at a site ~40 km south of the Boso Peninsula. Geochemical analysis has identified the shallow submarine Oomurodashi volcano as the source of this tephra. Here we present FTIR H2O species concentrations for different size fractions from this tephra and use them to investigate eruption processes of this explosive shallow marine eruption. We highlight that similar FTIR volatile analysis has the potential to yield new insights into tephra deposits contained in marine sedimentary archives.