Mineral component analysis of the Egersund dike system in Southern Norway

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The Ohio State University

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Recently CFBs or Continental Flood Basalts have become an area of interest for researchers of petrology. CFB eruption is believed to be involved with many of the eath's vital processes such as continental breakup, extinction events and crustal accretion. Athough it is not formally known as a major CFB province, the Egersund Dikes in SW Norway provide a fresh and accessible sample of these types of basalts. There has been speculation as to just how CFBs evolve in the mantle, specifically whether or not subduction is involved. A detailed study of the chemical composition of plagioclase feldspar, olivine and pyroxene was performed for this study. Relative percentages of each mineral in terms of its end members was obtained and plotted onto several phase diagrams. Electron microprobe analyses of pyroxene grains were used in an attempt to determine whether the samples from the Egersund dikes were calcalkaline or tholeiitic in nature. An FE-enrichment trend normally diagnostic of tholeiites was not detected in the graphs, however a plot of SiO2 vs. FeO/MgO revealed all of the samples to be tholeiitic. It was determined from lack of experimental data that the dikes are in fact tholeiitic and that subduction was not a factor in the genesis of these dikes.