Magmatic evolution of volcanic rocks near Stocking Lake, Ladysmith

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Issue Date
2019-04-09
Authors
Dean, Nicole
Young, Max
Strom, Maegan
Ahl, Dylan
Lee, Jessica
Guo, Zitian
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Abstract
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.
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