Age and provenance of Archean basement and Paleoproterozoic supracrustal rocks within Wopmay orogen

English Abstract:

The Paleoproterozoic Wopmay orogen is bounded in the east by the Slave craton. Bisecting the orogen is the Wopmay fault zone (WFZ) and west of it is the >1.93-1.89 Ga Hottah terrane and 1.875 to 1.85 Ga Great Bear magmatic zone. East of WFZ and west of Slave craton, polydeformed Neoarchean rocks are overlain by Paleoproterozoic strata. In one interpretation, these rocks began as part of the Hottah terrane, were thrust over the Slave craton during Calderian orogeny, and are preserved as a klippe (“Turmoil klippe”). Other interpretations suggest these Archean rocks are reworked from the Slave craton.

The extent and character of Archean rocks in the southern Wopmay orogen (between 63°N and 66°N) has been refined through bedrock mapping, U-Pb geochronology, and Nd isotope geochemistry. Results indicate the Mesoarchean and ca. 2580 Ma plutonic rocks have a Slave craton provenance, including those in the type section to the Turmoil klippe (Bent gneiss). Screens of Archean supracrustal rocks occur within granites and are correlatable to the Duncan Lake Group of the Slave craton. Paleoproterozoic quartzite, marble, and siltstone were deposited directly on deformed Archean basement and exposed as a series of domes and basins, metamorphosed between greenschist and granulite grade. Detrital zircons from the overlying quartzites have 2.7, 2.67, 2.60, 2.58 Ga, and 2.03 Ga ages, supporting a provenance from the Slave craton and the initial rift in Wopmay orogen. One sample contains the Slave spectra, along with ca. 2.33, 1.97, and 1.93 Ga detrital zircons that are similar to the Hottah terrane and Taltson magmatic zone. These strata may best be correlated to the Akaitcho Group, although a high component of Slave detritus has not been previously recognized in these sedimentary rocks.

The Archean rocks in Wopmay orogen began as part of the Slave craton. However, ca.2580 Ma granitic rocks in the Slave craton are not deformed, whereas those in Wopmay orogen underwent ductile deformation prior to and after deposition of the overlying strata. The post-Archean deformation is interpreted to be a result of initial rifting at ca. 2.02 Ga, followed by post-sedimentation folding and thrusting. The area east of WFZ is interpreted as an imbricate structure (duplex?) shoved over the western margin of the Slave craton during ca. 1.88 to 1.85 Ga deformation.