Major and Trace Element Analysis of Cayman Island Trough Basalts

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Student Presentation

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Dorsey Wanless


Here I present major and trace element concentrations of eight basaltic lavas erupted at the Cayman Trough, the slowest (20-40 mm/yr) and deepest (~5 km water depth) spreading center on the global mid-ocean ridge system. The tectonic setting of this mid-ocean ridge is complicated by nearby subduction and left lateral shear coupled with hydrothermal and contact metamorphism. Previous research in the 1970’s on basalts measured high concentrations of incompatible elements (Zr, Y, Sr, and Ba) in the volcanic glasses. Pyroxene-olivine-plagioclase three-phase crystallization of the melt is hypothesized to be the reasoning for the major and trace element variation, but only phenocrysts of plagioclase and olivine occur in the lavas. Here I reexamine the role of fractional crystallization in the formation of Cayman Trough lavas using Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS). Handpicked pieces of basaltic glass, while avoiding phenocrysts and alterations, are cleaned, polished, mounted in epoxy, and measured 3-5 times. These results are used to create Rare Earth Element, AFM, and ternary diagrams and Magnesium numbers in order to determine the extent of fractional crystallization and the nature of the magma from which these basalts formed.

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