Melt inclusion geochemistry and thermobarometry of historic lavas on the Reykjanes Peninsula, SW Iceland

• Main Author: Ingibjörg Þórðardóttir 1997-
• Other Authors: Háskóli Íslands
• Format: Master Thesis
• Language: English
• Published: 2022
• Subjects: Jarðfræði (námsgrein); Brennisteinsfjöll; Krýsuvík; Mid-Atlantic Ridge; Reykjanes; Iceland
• Online Access: http://hdl.handle.net/1946/41381

The Reykjanes Peninsula in SW Iceland is a 65 km long onshore continuation of the Mid-Atlantic Ridge composed of five volcanic systems that have all produced basaltic lavas in historic times. The Reykjanes, Svartsengi, Krýsuvík and Brennisteinsfjöll systems erupted during a 300-year period from ca. 940 – 1240 A.D whereas the Fagradalsfjall system had been dormant for more than 6000 years before the eruption in Geldingadalir in 2021. Determining the geochemical signature of melt inclusions within each volcanic system in context of historic volcanism provides a snap-shot view of parental melts from compositionally distinct mantle sources. In this work, I present a comprehensive dataset of major and minor element compositions of melt inclusions, groundmass glass, plagioclase, olivine and clinopyroxene macrocrysts from 10 historic lavas erupted across the Reykjanes Peninsula. Macrocryst cores are in most cases not in equilibrium with their carrier melt and are suggested to have crystallized from more primitive and heterogeneous parental melts. There is a geographical trend in which compositions get more primitive from west to east, reflecting an influence from the Icelandic mantle plume. Thermobarometers reveal that the Reykjanes, Svartsengi and Brennisteinsfjöll systems possess magma reservoirs within the crust. Primary melts are suggested to originate from 20-25 km depths within the Reykjanes system, 5 km within the Svartsengi system, 20-24 km within the Brennisteinsfjöll system and over a large range of 7-33 km within the Krýsuvík system. K2O/TiO2 ratios in MIs display significant compositional variability, especially within the Krýsuvík system (0.02 – 0.42). This variability likely reflects heterogeneous mantle sources composed of multiple compositional endmembers. Based on these data, parental melts within each volcanic system have a distinct mass balance between enriched and depleted endmembers. Reykjanesskaginn á Suðvesturlandi er 65 km langur og er beint framhald af Mið-Atlantshafshryggnum. Skaginn ...