Major and trace element geochemical analysis of norites in the Hakefjorden Complex to constrain magma source and magma plumbing systems

University essay from Lunds universitet/Geologiska institutionen

Abstract: Major and trace element data taken from plagioclase crystals from anorthosites and related rock units in the Hakefjorden Complex located off the west coast of Sweden were investigated for the purposes of constraining magma chamber processes and the source of the magma. Although the anorthosite units were completely homogenous in regards to its chemistry, the plagioclase in the associated norite and ilmenite-leuconorite units showed substantial variation. The zoning profiles of the aforementioned plagioclase units showed sudden increases in Sr in the rims of the plagioclase. These patterns are likely to be caused by replenishment of the magma via recharge events. Peaks in An content coincide with patchy disequilibrium textures at the rims of the crystals - these are linked to either decompression via polybaric evolution of the magma chamber, magma recharge events or a combination of both. The peaks in trace element concentrations also coincide with the disequilibrium textures, which provide evidence that the recharge events are linked to the ascent of the magma chamber. The evidence of recharge events and the homogenous nature of the 87Sr/86Sr zoning profiles as indicated by Glommé (2015) suggest that a mantle derived source with crustal contamination is unlikely, and instead favours a lower crustal magma source.

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