New Insights into Archean Crustal Development from Geochronology in the Rainy Lake Area, Superior Province, Canada

Abstract

Precise isotopic analyses of zircon, titanite, and rutile from units in the Rainy Lake area of northwest Ontario are combined with structural investigations to develop new stratigraphic interpretations in which lithotectonic sequences were juxtaposed by thrusting prior to steepening by wrenching. Ages for the oldest volcanic and plutonic rocks in the area range from $2725 \pm 2 Ma to 2728 +4/-3 Ma$. The age of metagray-wackes of the Coutchiching Group is bracketed between $2704 \pm 3 Ma$ and $2692 \pm 2 Ma$ by detrital zircon and a crosscutting intrusion. Alluvial conglomerate of the Seine Group is bracketed between 2696 +5/-3 Ma, the age of a clast, and 2686 +2/-1 Ma, the age of the undeformed Ottertail Lake Pluton. The Coutchiching Group is younger than structurally overlying metavolcanic rocks and is therefore allochthon-ous. These data suggest that sedimentation and deformation were controlled by collisional plate interactions and subsequent transpression at the subprovince boundary. Combined with dat...