The Picton and Varty Lake ultramafic dikes: Jurassic magmatism in the St. Lawrence Platform near Belleville, Ontario

Publisher Website
Google Scholar
Abstract
The Picton and Varty Lake ultramafic dikes that intrude Ordovician limestone near Belleville, Ontario, consist of olivine or serpentinized pseudomorphs and Ti-phlogopite phenocrysts set in a groundmass of spinel, perovskite, serpentine, calcite, apatite, and chlorite. Phlogopite exhibits a complex chemical variation and late-stage Ba enrichment (up to 6.8 wt.% BaO). Spinels are chemically zoned and commonly exhibit an atoll texture in which a magnesian–aluminous chromite core is separated by a silicate zone from late-stage magnesian–aluminous titanomagnetite chemically similar to kimberlitic spinel. Atoll spinels from the Picton dike also have a zone of titanian pleonaste surrounding a central grain of magnesian–aluminous chromite at the centre of the atoll structures. Both dikes are extremely silica undersaturated, with high K/Na and Mg/(Mg + Fe2+) ratios. Petrographic and chemical features of the Picton and Varty Lake dikes preclude simple classification, as both dikes have aspects indicative of kimberlitic and lamprophyric affinities. K–Ar age determinations, indicating a Jurassic age of emplacement for both dikes, are supported by paleomagnetic data from the Picton dike. The Varty Lake dike yielded no stable paleomagnetic remanence directions; limestone adjacent to the dike retains a Paleozoic remanence possibly indicating a very low emplacement temperature. The emplacement of both dikes may be related to Grenville-age basement faults reactivated in Jurassic time.

This publication has 0 references indexed in Scilit: