Integrated geospatial-geochemical catchment analysis of Newfoundland stream waters draining endmember silicate bedrock types (ultramafic-mafic rocks vs. granite)

Ledesma, Gabrielle Maria (2024) Integrated geospatial-geochemical catchment analysis of Newfoundland stream waters draining endmember silicate bedrock types (ultramafic-mafic rocks vs. granite). Masters thesis, Memorial University of Newfoundland.

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Abstract

The dissolved inorganic element chemistry of stream waters is a reflection of local bedrock composition, but also other catchments properties such as hydrology, surficial geology, vegetation/soil type, and elevation. Studies from small hydrological catchments with a singular or restricted range of bedrock type(s) are ideal for isolating geologic controls on water chemistry from other physicochemical and environmental controls. This study assesses dissolved major, trace, and rare earth element data from streams at two study sites within the same (boreal) climate zone of Newfoundland that each drain a silicate-endmember bedrock composition: (1) Bay of Islands in western Newfoundland draining an ophiolite sequence of mafic/ultramafic bedrock, and (2) Burin Peninsula draining a large Devonian carboniferous granite pluton (St. Lawrence granite) that hosts fluorite mineralization. Through integrating geochemical data with geospatially quantified catchment property data, this study has isolated the elements most strongly controlled by: bedrock geology (Mg, Cr, Ni in ultramafic rock streams; Cs, Rb in granite streams; contrasting REE abundances and Eu anomalies); weathering/soil/vegetation effects and associated flux of dissolved organic matter to streams (K, Co, Ce anomalies); and short temporal events or local geological features such as the fluorite mineralization (elevated element flux, high Y/Ho). Several of these more local water chemical features were traceable into larger catchment areas of Newfoundland major rivers. The low-abundance trace element data are the first to be reported for any Newfoundland surface water and have exposed this research approach as useful to trace boreal catchment dynamics through the lens of trace element geochemistry.

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