Midway evaluation in Geology - Bryndís Ýr Gísladóttir

Title of thesis: Chemical and physical characterization of the lower crust beneath the Reykjanes Peninsula based on crustal xenoliths

Student: Bryndís Ýr Gísladóttir

Doctoral committee:
Enikö Bali, Professor at the Faculty of Earth Sciences, University of Iceland
Halldór Geirsson, Professor at the Faculty of Earth Sciences, University of Iceland
Sæmundur Ari Halldórsson, Research Professor at the Institute of Earth Sciences, University of Iceland
John Maclennan, Professor at the Department of Earth Sciences, University of Cambridge, UK

Abstract

The recent volcanic activity of the Reykjanes peninsula has opened new opportunities to study the processes occurring within the crust beneath the region. The 2021 eruption in Fagradalsfjall was the first eruption in nearly 1000 years, and during the eruption, magma transported various crustal derived xenoliths to the surface. These xenoliths provide us with important information on the chemical composition, the structure and the processes on going within the crust. By analyzing their petrographic features and chemical composition, including textures, major- and trace elements, and isotopic signatures, it is possible to reconstruct key physical and chemical processes within the crust. These include crystallization and cooling history of the magma reservoir(s), partial melting of the crust, magma recharge and magma mixing within the system. All which shapes the given portion of the crust before volcanic eruptions. They can also provide key petrological and geochemical constraints on the parameters that control rheology at depth. Since these xenoliths are a good way to characterize the lower portion of the crust, which is inaccessible by drilling, we expanded the research to a wider area, as xenoliths can be found in various localities in the Reykjanes peninsula. We acquired xenoliths from 10 other locations with the goal of comparing these xenoliths to the ones brought to the surface by the Fagradalsfjall eruption. These other locations range from the tip of the peninsula (Stampar/Háleyjabunga) in the west to Miðfell by Þingvellir in the east, and from Selhraun by Hafnafjörður down to Stóra Eldborg and Hrólfsvík in the south. With this distribution of xenoliths, the petrological and chemical characterization of the crust below Reykjanes peninsula can be covered from east to west and also from north to south. The study aims first to characterize the petrography, mineral chemistry and geochemical composition of the xenoliths from across the peninsula and to use this data to reconstruct magmatic and crustal processes at depth. And secondly to link the petrological and geochemical characteristics of the xenoliths to physical parameters such as seismic velocity and viscosity, thereby constraining the mechanical behavior and rheology of the lower crust beneath the peninsula. In this talk I will present the theoretical background of my research with my preliminary results and future tasks which ensure the completion of this PhD project.