Physical, chemical, and fluid evolution of a Palaeoproterozoic submarine volcanic system, Bravo Lake Formation, Baffin Island, Nunavut, Canada.

摘要

Rocks of the Bravo Lake Formation on Turtle Back Island and Pillow Island off the western coast of central Baffin Island, Nunavut, represent a well-exposed example of the mafic volcanic and intrusive sequences commonly preserved near the base of Palaeoproterozoic intracratonic basins in the Archean Rae and Hearne Provinces of the Canadian Shield. The Bravo Lake Formation is composed of undeformed amygdaloidal pillowed flows, radial columnar and tortoise-shell jointed pillows, hydroclastic breccia, dyke swarms, mafic sediments, massive flows, and layered and megacrystic intrusions. Volcanic structures and textures imply emplacement in a low-energy shallow submarine environment. Submarine hydrothermal alteration mobilized Ba and Rb, and was followed by dry closed system amphibolite facies regional metamorphism. Co-existing mineral assemblages and stable isotope and cation exchange geothermometry from the Bravo Lake Formation indicate preservation of submarine hydrothermal alteration at ∼300°C, amphibolite facies regional metamorphism at ∼590°C, and retrograde metamorphism at ∼300°C. (Abstract shortened by UMI.)