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Helium, carbon and nitrogen isotope evidence for slab influence on volcanic gas emissions at Rabaul caldera, Papua New Guinea

Brendan MCCORMICK KILBRIDE1, Peter BARRY2, Tobias FISCHER3, Greg HOLLAND1, Michael HUDAK4, Scott NOWICKI3, Chris BALLENTINE5; Olivier BERNARD6; Michael FOX7; Margaret HARTLEY1; Melina HOEHN1; Ima ITIKARAI8; Maggie Johnson7; Kila MULINA8; Emma NICHOLSON9,10

  • Affiliations:  1Department of Earth Sciences, University of Manchester, UK; 2Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, USA; 3Department of Earth and Planetary Sciences, University of New Mexico, USA; 4Department of Geosciences, Williams College, USA; 5Department of Earth Sciences, University of Oxford, UK; 6Institut de Physique du Globe de Paris, France; 7Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Saudi Arabia; 8Rabaul Volcanological Observatory, Papua New Guinea; 9Department of Earth Sciences, University College London, UK; 10Department of Earth Sciences, University of Waikato, New Zealand 

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 267

  • Programme No: 3.17.36

  • Theme 3 > Session 17

Abstract

The chemical and isotopic composition of arc volcano gases offers insights into the origin of magmatic volatiles. In volcanic arcs, magmatic volatiles can be supplied from the mantle, the subducting slab, or the rocks of the arc crust. Determining the relative contributions of these distinct sources is important for understanding the transfer of volatiles between Earth's interior and exterior reservoirs, which has implications for the physical and chemical evolution of the mantle and the atmosphere. Each subduction zone has a different recycling efficiency, controlled by the composition of the slab and the pressure-temperature path it experiences upon subduction. Thus, all volcanic arc emissions can be characterised by their chemical and isotopic compositions. In this study, we analyse the composition of volcanic gases from Rabaul caldera in the New Britain subduction zone, Papua New Guinea, and show that the emissions are substantially influenced by slab recycling of carbon and nitrogen. We find helium emissions are dominated by a mantle contribution, with little crustal influence. Carbon isotopes point towards a mixture of mantle, carbonate and organic sediment-derived contributions, with the dominant input coming from carbonates. This may be of sedimentary origin, seafloor calcareous muds, or altered basalts of the subducting oceanic crust. Nitrogen isotopes also indicate a significant influence of sedimentary nitrogen. Our study is the first comprehensive investigation of volatile sources in the New Britain subduction zone and our results and interpretation are consistent with previous studies of element recycling based on New Britain arc lavas.