PETROGENESIS, AGE, AND CORRELATION OF THE KAZAN DIKE SWARM, NUNAVUT, CANADA: IMPLICATIONS FOR AN ABORTED RIFT ORIGIN FOR THE SNOWBIRD TECTONIC ZONE

The Snowbird Tectonic Zone (STZ) is a 2800 km long geophysical lineament proposed as the boundary between the Rae and Hearne cratons within the western Churchill Province. Although the origin and tectonic significance of the STZ remains enigmatic, at the latitude of Angikuni Lake, Nunavut strain is distributed along shear zones that juxtapose lithotectonic domains of varying metamorphic grade and structural style. A suite of undeformed diabasic to gabbroic Kazan dikes crosscuts all rock units at Angikuni Lake, including faults delineated by an extensive network of granitic breccias. The dikes are subvertical, generally less than 10 m wide, and trend mainly NE-SW (parallel to the Tulemalu fault zone and STZ) although they form intersecting reticulate networks. Igneous texture is often preserved despite extensive secondary alteration by epidote, chlorite, phyllosilicates, and calcite; features shared with the breccias they commonly crosscut. In some samples garnet crystals rim former plagioclase grains, indicating a static post-intrusion metamorphic event. U-Pb zircon ages from rare, euhedral zircon crystals in the dikes yield an age of ca. 2.1 Ga, limiting the time of major movement along STZ-related structures. Metamorphic zircon rims in the dikes and on zircon from other lithologies yield ages of ca. 1.84 Ga. The rims formed from the far-field effects of Hudsonian orogenesis and/or initiation of bounding faults to Baker Lake Basin. Similar mafic bodies extend along the STZ and include the Chipman dikes and Clearwater batholith over a minimum length of > 800 km. In contrast to the Griffin Gabbros (ca. 2.11 Ga), emplaced as sills into the Hurwitz Group (Paleoproterozoic), Kazan dikes at Angikuni Lake were emplaced vertically within Neo- and Mesoarchean crust near the STZ and, in general, have older Nd depleted mantle ages. All ca. 2.1 Ga mafic dikes and sills (Angikuni, Griffin, and Chipman) are likely part of a major large igneous province generated by tapping of enriched asthenospheric mantle during opening of the Maniwekan Ocean.