Magmatic evolution of volcanic rocks near Stocking Lake, Ladysmith
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The Stocking Lake area, located south of Ladysmith, B.C., has been previously mapped as middle Devonian Nitinat formation belonging to the Sicker arc volcanics, and hosting an intrusion of Upper-Triassic Mount Hall Gabbro. The evolution of each sample and a comparison to previously published regional data from the Sicker and Karmutsen formations are examined through thin section and major oxide geochemical data in order to answer the following hypotheses: • If the samples originate from the same magma chamber then linear trends are expected to plot on both Harker bivariate and scandium-pyroxene fractionation diagrams and thin section analysis will show similar mineral assemblages between samples, despite the variation in texture. • If sample LS-19-07 is pyroclastic then the thin section will show fragmented crystal assemblages and devitrification of the glassy matrix into radiating crystal lathes. • If the volcanic rocks originated in an island arc setting, they should show a calc-alkaline geochemical signature when plotted on an AFM diagram. If a tholeiitic signature is observed the AFM diagram is inconclusive and a tectonic discrimination must be plotted. • If the existing regional data sets and maps are correct, our major oxide geochemical data will indicate that all samples belong to the Nitinat formation except for sample LS-19-29, which should belong to the Mt Hall Gabbro. We hypothesize that the local Nitinat deposit is not a series of separate flows, as it may appear, but one eruptional event varying in magmatic composition and texture due to crystal-melt segregation and liquid extraction.