Abstract

Mafic pillowed and massive lavas of the Upper Carboniferous West Beach Formation, as exposed in the city of Saint John, southeastern New Brunswick, were metamorphosed under prehnite–pumpellyite facies conditions, possibly between 315 and 370 °C and 1 and 2.5 kbar (105 and 2.5 × 105 kPa). Petrographic and chemical data for 32 samples indicate that this metamorphism was accompanied by significant silicification of some samples and variable chloritization of most. These processes caused relatively minor chemical transfer of most elements other than silica, and calculations from averages assuming constant Al indicate that TiO2, P2O5, Zr, Rb, Nb, Ga, and Y are relatively immobile. However, ratio diagrams show anomalous concentrations of these elements in a few samples and illustrate the inherent flaws of quantitative estimates based on averages. Classifications using these elements in a variety of diagrams clearly and consistently indicate a primitive calc-alkaline nature for the lavas, contrary to what might be expected from their geological setting interbedded with plant-bearing paralic or continental sedimentary rocks.

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