Bravo Lake Formation

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The Bravo Lake Formation is a mafic volcanic belt and large igneous province^[1] located at the northern margin of the Trans-Hudson orogeny on central Baffin Island, Nunavut, Canada. It is exposed along a nearly continuous east-west passage for 120 km (75 mi) and changes in stratigraphic thickness from 1 to 2.5 kilometers.^[2] The formation is a rare alkaline-suite that formed as a result of submarine rifting during the Paleoproterozoic period.^[3] The Bravo Lake Formation is surprisingly undeformed by the Himalayan-scale forming event during the Trans-Hudsonian orogeny.

The stratigraphy of the Bravo Lake Formation starts with a basic section of iron-oxide rich sandstones, psammites, and semi-pelites cover a series of deformed pillow lavas expanding in viscosity towards the west, and volcanic/clastic deposits and ultramafic sills. The lower volcanic section is covered by garnet and diopside bearing calc-silicate layers and finely layered metasediments comprising of course-grained actinolite/hornblende/biotite followed by pelites and semi-pelites that are intruded by separated sills. In the Ridge Lake area, the volcanic belt includes an interlayered series of amphibolite, gabbro, iron formation, sulphidic schist and metasediments.^[2]

Geochemical results of pillow lavas and chill boundaries along five transects across the volcanic belt suggest the existence of three chemically different magma types within the Bravo Lake Formation.^[2]

Lavas of the volcanic belt display geochemical characteristics similar to modern ocean-island-basalt groups. They range from moderately to intensely fractionated REE-profiles is similar to that from tholeiitic basalts to extremely alkaline lavas in Hawaii.^[2]