Formation of the Neoarchean Bad Vermilion Lake Anorthosite Complex and Spatially Associated Granitic Rocks at a Convergent Plate Margin, Superior Province, Western Ontario, Canada.

摘要

The Neoarchean Bad Vermilion Lake Anorthosite Complex (BVLA Complex) is one of the most well-exposed, anorthosite-bearing, Archean layered intrusions in the Superior Province. Zircons from the intruding granitic rocks have yielded a 207Pb/206Pb age of 2716 +/- 18 Ma, constraining the minimum intrusion age of the complex.;Mantle-like oxygen isotope signatures of the anorthosites and trace element patterns in the various units of the BVLA Complex suggest that they were derived from melting of a shallow source in a subarc mantle wedge. The existence of primary calcic igneous plagioclase, coherent Nb negative anomalies, and geochemical similarities between gabbros from the BVLA Complex and gabbros from Cenozoic arcs collectively suggest an intra-oceanic subduction zone geodynamic setting for the complex.;Compositionally, the bordering granitic rocks are A2-type. We suggest that they formed in a post-collisional, extensional, tectonic regime following emplacement of the BVLA Complex in an oceanic arc.