The Central Slave Basement Complex, Part I: its structural topology and autochthonous cover

Abstract

New field and geochronological data are used to define the distribution of Mesoarchean basement rocks in the south-central Slave Province. This distribution reflects a single contiguous basement terrane that we propose to call the Central Slave Basement Complex. It shows a structural topology that is internally consistent and compatible with known regional folding and faulting events. A sample of a proposed basement gneiss below the Courageous Lake greenstone belt, central Slave Province, has been dated by U-Pb methods and yields an age of 3325 ± 8 Ma, consistent with the new basement distribution. This sample also contains 2723 ± 3 Ma metamorphic zircon and ca. 2680 Ma titanite. The Central Slave Basement Complex is overlain by a thin, discontinuous, but distinctive cover sequence that includes minor volcanic rocks, clastic sedimentary rocks, and banded iron formation. All previously known and some new occurrences of this distinctive cover sequence occur in the immediate stratigraphic hanging wall of the Central Slave Basement Complex, locally overlying a preserved in situ unconformity. We propose to call this post-2.93 Ga cover sequence the Central Slave Cover Group. It is perhaps best typified by detrital chromite-bearing, fuchsitic quartzites. Formal formation names are proposed for the spatially separate occurrences of the Central Slave Cover Group. Detrital zircon ages are presented for one of the formations of the Central Slave Cover Group, the Patterson Lake Formation, which occurs on the western flank of a local basement culmination known as the Sleepy Dragon Complex. The detrital zircon data provide evidence for two discrete basement sources dated at ca. 2943 Ma and ca. 3147-3160 Ma. These detrital ages reinforce the depositional link between the Central Slave Cover Group and underlying crystalline rocks of the Central Slave Basement Complex.

sedimentary facies analysis of the >2.8 Ga Beniah and Bell Lake formations, Slave Province, Northwest Territories /

“…1) the Dwyer and Bell Lake areas (Jackson 1996;; 2) Beniah Lake (Covello et al 1988;Roscoe 1990;Roach & Fyson 1992); 3) Beaulieu River (Rice et al 1990); 4) Winter Lake (Hrabi et al 1993) and the 5) Patterson and Brown Lake areas (Bleeker et al 1999). The stratigraphy of this older sedimentary sequence is the focus of this study, with emphasis on Beniah and Bell lakes.…”

“…2722 Ma Figure 3.1. Stratigraphie columns illustrating the general stratigraphy of the Bel Lake group/formation described by Â) Isachsen and Bowring 0997) and B) Bleeker et al (1999).…”

“…The mineralogy of the QAL is extremely quartz-rich and is composed of medium-to coarse-grained quartz, muscovite and subordinate feldspar. The QAL also contains mm-size, subrounded detrital chromite grains that are often enveloped by seams of green mica formed by reaction between chromite and feldspar grains during shearing and metamorphism (Bleeker et al 1999). Locally, the quartz-arenite beds are intercalated with fine-to medium-grained sandstones (< 30 cm thick) that are generally dark, poorly to moderately sorted and contain laminae parallel to the north-trending fault zone.…”

“…1986;Lambert et al 1992;MacLachlan & Helmstaedt 1995;Bleeker et al 1999) Based on structural measurements and deformation patterns, at least two series of mafic dykes have been found to predate deposition of the Yellowknife Supergroup. These include mafic dykes mapped in the Fenton-Brown lakes area (James & Mortensen 1992) and in the Sleepy Dragon Basement Complex (Kusky 1990).…”

“…Figure 5.1 illustrâtes the location of these basins as well as the extent of the gneissic basement complexes mapped by Bleeker et al (1999) and . It is observed that the basement and overlying ~2.8 Ga sedimentary rocks are all found adjacent to norm-trending crustai-scale faults, such as the Beniah Lake and the ancestral Jackson Lake fault zones .…”