Háskóli Íslands

The defence will be streamed live

Ph.D. student: Eemu Ranta

Dissertation title: Stable isotopes of volatile elements as a window into the crust and mantle beneath Icelandic volcanoes

Opponents: 
Dr. Jacqueline E. Dixon, Professor at the College of Marine Science, University of South Florida, USA
Dr. James Farquhar, Professor at the Department of Geology, University of Maryland, USA

Advisors: Dr. Sæmundur Ari Halldórsson, Research Scientist at the Institute of Earth Sciences, University of Iceland
Dr. Andri Stefánsson, Professor at the Institute of Earth Sciences, University of Iceland

Doctoral committee: 
Dr. Peter H. Barry, Assistant Scientist at the Woods Hole Oceanographic Institution, USA

Chair of Ceremony: Dr. Freysteinn Sigmundsson, Research Scientist at the Institute of Earth Sciences, University of Iceland, and the Head of the Faculty of Earth Sciences, University of Iceland

Venue: Askja - room 132 - Febrary 25th at 14:00.

Abstract:
Volatile species (e.g., H2O, He, B, CO2, S, Cl) and their isotopes in volcanic materials provide a unique, but underexplored archive of information about magmatic processes and planetary evolution. This study aims to improve our understanding regarding the origins of volatiles in ocean island basalts and the roles played by volatiles in evolving magmas in the crust. To this end, data are presented on the abundances and isotopic compositions of volatiles in lavas and hydrothermal fluids from active volcanoes in Iceland. Special focus is given to the Kverkfjöll volcanic system, for which a comprehensive geochemical dataset is provided.

The main results are: (1) Chlorine isotope ratios of silicic volcanic rocks are introduced as a novel tracer of fluid-melt interaction in silicic magma domains, showing that magmatic brine assimilation may be a fundamental, but previously unrecognized process during rhyolite genesis. (2) Sulfur isotopic compositions of Icelandic basalts are shown to reflect both crustal magma evolution and mantle heterogeneity. Distinct Δ33S-δ34S signatures are assigned for recycled and primordial mantle components. (3) Deep intrusive degassing is identified as the source of CO2 and S in Icelandic volcanic-hydrothermal systems, which are proposed to be the main conduits of mantle-to-atmosphere degassing for these volatiles. (4) The geochemistry of the Kverkfjöll magma suite highlights the lithospheric lid control on mantle melting, and an asymmetric distribution of enriched components in the Iceland mantle (5) A subduction fluid-enriched mantle component beneath Iceland is suggested to explain the chlorine-enrichment and back-arc basin-like isotopic signatures of hydrogen, helium, boron, sulfur and chlorine of the Kverkfjöll basalts.

About the doctoral candidate:

Eemu Ranta was born in 1989 and grew up in Tampere, Finland, Grenoble, France, and Gothenburg, Sweden. Eemu received a BSc degree in Earth Sciences from Stockholm University in 2015 and a MSc degree in Geology from the University of Helsinki in 2017. Aided by a NordVulk fellowship, Eemu relocated to Reykjavik in August 2017 together with his partner, visual artist Pauliina Jokela, and their now 7-year-old child Neeme, to pursue doctoral studies at the University of Iceland.

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