Crystal settling and in-situ magma differentiation in Neoproterozoic sills of the Franklin Igneous Event, Victoria Island, NWT, Canada.

摘要

There are a series of thin, laterally continuous, Proterozoic (~720Ma) sills exposed on the northern limb of the Holman Island Syncline, exposed at 72°N latitude on Victoria Island, NWT. This study examines two of these sills for vertical changes in composition, thickness, sorting, and texture to better understand their crystallization histories. The sills in this study are on the order of 21 to 26 meters thick, have thick olivine-rich mafic bases, which in some cases are overlain by a thin augite-rich zone, and a thick diabasic upper section.;Chemical modeling using variation diagrams, Pearce-element-ratio-analysis, MgO mass-balance calculations, least-squares fit modeling, and trace element analysis, suggest that these thin sills were emplaced as phenocryst-rich magmas, followed by the settling of initial phenocrysts and rapid cooling, without significant post-emplacement in-situ differentiation to produce the observed chemical variations.