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Recovery of geochemical processes in komatiites using linear algebraic methods Hilchie, Luke


The metasomatic reactions responsible for the mineralogical and chemical alteration of komatiites have not been fully identified. The geochemical effects of these reactions inhibit recovery of the nature and extent of magmatic processes recorded by komatiite rocks. Metasomatism is a challenge in lithogeochemical research because protolith variability and metasomatism together define high-dimensional geochemical spaces. Standard methods that require a conserved element are of limited use, as conserved elements may not be present. This work develops and applies linear algebraic techniques to test mass transfer hypotheses against whole rock compositions without assumptions of elemental behaviour. The methods enabled quantification of the stoichiometry and the relative effects of magmatic and metasomatic processes in komatiites. Such processes include magmatic differentiation, serpentinization, and breakdown of clinopyroxene to actinolite. Three main findings are: (1) geochemical and petrological evidence exists for within-flow differentiation and the possibility of lateral continuity between komatiite and komatiitic basalt flows; (2) serpentinization occurred neither by isochemical nor fully metasomatic processes in a lava flow from Pyke Hill in the Abitibi greenstone belt; and (3) small magnitudes of metasomatic reactions are sufficient to modify primary geochemical signals, such that their neglect in geochemical interpretation could lead to incorrect conclusions. Future studies could delve deeper into the possibility of lateral continuity between komatiites and komatiitic basalts, and expand determination of viable serpentinization reactions to a wider range of localities and lithologies.

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