Physical volcanology, geochemistry, and tectonic evolution of three selected areas in the Point Lake and Beaulieu River volcanic belts, Slave Province, Northwest Territories, Canada

The ca. 2.67–2.70 Ga Point Lake, Northern Beaulieu River and Central Beaulieu River volcanic belts in the Slave Province, Northwest Territories, Canada, represent portions of a continental arc to back-arc sequence that evolved over approximately 30 m.y. Inferred west-dipping subduction of an oceanic slab beneath sialic crust resulted in the development of a continental arc at least 250 km long. Physical volcanology and geochemistry of the volcanic rocks indicate that the Peltier Formation of the Point Lake belt formed in a back-arc basin overlying continental crust, the Northern Beaulieu River belt represents the transition zone between the arc and back-arc, and the Central Beaulieu River belt developed in the arc.; The Peltier Formation overlies the 3.22 Ga Augustus Granite, is interstratified with the >2.65 Ga turbiditic Contwoyto Formation, and is associated with 2.68 Ga felsic-intermediate volcaniclastic rocks of the Samandré and Beauparlant Formations. The mafic-dominated volcanic sequence is consistent with the proximal to distal portions of seamounts in deep to moderate water depths. The proximal facies include a non-vesicular pillowed sequence cut by numerous mafic intrusions, typical of the central, deep water portion of seamounts. The medial to distal, moderate depth facies are represented by pillow breccia, hyaloclastite (peperite), and pillowed and massive flows with 5–27% vesicularity. Interstratified shale units and peperite indicate contemporaneous sedimentation and volcanism. Mafic rocks in the Peltier Formation range from NMORB through tholeiitic LREE-enriched EMORB with Nb and Ti depletions, to strongly LREE-enriched calc-alkaline compositions with Nb and Ti depletions. ϵ_Nd values are from −2.94 to +3.06 and increase with decreasing (La/Yb)_n ratios. Insulation of the conduit walls during ascent of early magmas is considered to have limited the effects of crustal contamination over time.; The Northern Beaulieu River belt overlies the 2.95 Ga plutonic Beniah Complex, ultramafic units, and the 2.9 Ga Beniah Formation quartz arenites. Mafic volcanic facies are massive flows with subordinate pillowed flows and a paucity of fragmental debris, consistent with subaqueous fissure-fed volcanism and local seamount development. A significant mafic dyke complex indicates extension during evolution of the volcanic belt. Felsic volcaniclastic rocks are represented by a succession of planar- and cross-bedded lapilli tuff overlain by wary- and planar-bedded coarse tuff, grading into planar-bedded fine tuff with black tuff units, overlain by a pillowed flow. (Abstract shortened by UMI.)...