Geochemistry and geodynamic implications of the Mesoproterozoic English Bay granite–rhyolite complex, northwestern Ontario

Authors:
  • PHPete Hollings
    Pete Hollings
  • PFPhilip Fralick
    Philip Fralick
  • SKStephen Kissin
    Stephen Kissin
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Abstract
The Mesoproterozoic English Bay Complex consists of a granite-rhyolite assemblage outcropping on the shores of Lake Nipigon in western Superior Province, Canada. It intrudes Neoarchean rocks and is disconformably overlain by a rift–infracratonic basin sedimentary succession recording subsidence following a heating event. The granites and rhyolites are characterized by light rare-earth element (LREE) enrichment (La/Smn = 2.8–5.1) and only weakly fractionated heavy REE (HREE; Gd/Ybn = 1.1–1.6). The felsic igneous rocks are high-K, enriched in Zr, Nb, Y, and REE satisfying all the criteria for an A-type suite. Trace element geochemistry, particularly the absence of any negative Nb anomalies, indicates this melt did not originate in a suprasubduction zone setting, unlike the St. Francois Mountain Complex to the south. The English Bay Complex may record the northern portion of a Mesoproterozoic plume track— a plume that possibly led to earlier igneous activity and infracratonic basin formation to the north and would later interact with a suprasubduction zone margin to the south.

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