IN-SIMS zircon U-Pb geochronology from the Snowbird tectonic zone Large igneous Province (STZ LIP), western Churchill Province, Canada

•IN-SIMS zircon analysis yields a ca. 2.1 Ga age for Chipman and Kazan dike swarms.•Geochemical data suggests an asthenospheric-source for the STZ LIP swarms.•The STZ LIP underwent contamination by Neoarchean metasomatized lithosphere.•New data indicate that STZ dike swarms may be 2.1 Ga, and extend for > 800 km.•The STZ LIP formed during incipient rifting of a coherent Rae-Hearne boundary.•The STZ was reactivated during Hudsonian orogenesis from 1.98 to 1.80 Ga. IN-SIMS (in-situ secondary ionization mass spectrometry) micro-zircon geochronology resolves the age of the Chipman and Kazan mafic dike swarms exposed along the central segment of the Snowbird Tectonic Zone (STZ), the geophysically defined feature separating the Rae and Hearne subprovinces of the western Churchill Province. Long-considered syn-kinematic with respect to Paleoproterozoic transpressional deformation, the primitive composition of the STZ Large Igneous Province (LIP) and granulite grade metamorphic overprint has made establishing crystallization ages difficult. In-situ U-Pb isotopic analysis of micro-zircon yielded scattered and discordant results, except for four zircon crystals, which yielded a weighted mean of 2113 Ma +/- 22 (n = 8 analyses; MSWD: 0.46). This age is similar to other mafic complexes in the western Churchill Province including the Griffin Gabbro sills interpreted to have formed during opening of the Manikewan Ocean. Nd isotopic analyses of Kazan dikes paired with geochemical data suggest that the Chipman and Kazan dikes were asthenospherically-derived but contaminated by a metasomatized lithospheric root. At ca. 2.1 Ga, the STZ was the site of intracratonic extension within a coherent Rae-Hearne crustal block (Snowbird LIP Phase I). Existing data suggests that subsequent tectonism led to focused dextral transpression along the trace of the dike swarm and attests to a long-lived interplay of preexisting weaknesses and deformation.