Geology and thermotectonic evolution of the western margin of the Trans-Hudson Orogen: evidence from the eastern sub-Athabasca basement, Saskatchewan

Abstract

In the Cree Lake Zone of northern Saskatchewan, reworked Archean orthogneisses are overlain by a highly deformed supracrustal sequence, the Paleoproterozoic Wollaston Group. This package of rocks was deformed and metamorphosed during the ca. 1.8 Ga continent–continent collision of the Trans-Hudson Orogen (THO), forming the Wollaston fold–thrust belt that underlies the eastern Athabasca Basin. The Hudsonian structural, metamorphic, and magmatic evolution of the Wollaston fold-thrust belt in the eastern Athabasca area involved six major stages. (1) Early collisional stage, DP1 at 1860–1835 Ma, involved burial of Wollaston Group metasediments from surface to depths equivalent to 3–5vkbar (1 kbar = 100 MPa) by thrust-pile stacking or imbrication tectonics, prograde metamorphism with garnet growth and development of early leucosomes, and emplacement of ca. 1840 Ma grey granite suite. (2) Collisional stage, DP2a at 1835–1820 Ma, involved continued deeper burial of Wollaston Group metasediments along a prograde P–T–t (pressure–temperature–time) path at depths equivalent to peak pressures of 6–9 kbar and approaching peak temperatures (750–825 °C), mafic magma underplating in the lower crust, initiation of large-scale crustal melting, emplacement of 1835–1820 Ma tholeiitic to calc-alkaline intrusions, and initiation of strike-slip tectonics. (3) Oblique collisional stage, DP2b at 1820–1805 Ma, involved strong transpressional tectonics with NE–SW shearing and NW–SE shortening, partitioned high-strain ductile flow, kilometre-scale fold development, initiation of exhumation, attainment of peak temperatures (750–825 °C), and essentially isothermal decompression with decompressional melting and intrusion of the main pulse of leucogranites and granitic pegmatites. (4) Late oblique collisional stage, DP3 at 1805–1775 Ma, caused development of amphibolite-facies dextral strike-slip shear zones and retrograde movement of older shear zones. It included apparent rotation of the main shortening axis and development of accommodation features due to vertical uplift (i.e., extension). (5) Post-collisional stage, DP4 at 1775–1760 Ma, involved continued localized adjustments along an essentially isobaric cooling path and produced NNE-trending, sinistral, oblique-slip reverse faults with reactivation of older shear zones. (6) Late post-collisional stage, DP5, produced north- to northwest-trending sinistral faults, including the Tabbernor fault system. Extension and tectonic extrusion during DP4 and DP5 were significant and resulted in orogenic collapse and formation of the Athabasca Basin at ca. 1750–1680 Ma.

Geology and evolution of pegmatite-hosted U-Th ± REE-Y-Nb Mineralization, Kulyk, Eagle, and Karin Lakes region, Wollaston Domain, northern Saskatchewan, Canada: examples of the dual role of extreme fractionation and hybridization processes

“…The U-Pb ages constrain the emplacement of the pegmatite and mineralization to the well-documented magmatism (or hydrothermal-magmatic events) in the latter stages of Trans-Hudson Orogeny (THO) deformation at c. 1850-1760 Ma. The timing of pegmatite emplacement in the THO has previously been supported by U-Pb zircon and monazite ages from undeformed pegmatites in the Wollaston fold belt (Chiarenzelli 1989;Bickford et al 1990Chiarenzelli et al 1998;Annesley et al 2005;Schneider et al 2007;McKechnie et al 2012a, b).…”

“…Evidence demonstrating melt generation in the middle crust is apparent in the Key Lake and McArthur River mine areas, where dilatant zones were created during thrusting, strike-slip faulting, and/or extensional faulting that have focused crustal melts and partitioned strain (Annesley et al 2005). The tectonized contact between the Archean gneiss domes and the Lower Wollaston supracrustal rocks was the locus for magmatism, asso-…”

“…The studies showed that the Paleoproterozoic mafic and felsic intrusive rocks record variable degrees of contamination by Archean and older Paleoproterozoic crust, underlining the complex evolutionary history of crust along the western margin of the Trans-Hudson Orogen. The Wollaston Group metasediments overlie Archean granites that range between 2650 Ma and 2500 Ma (U-Pb zircon TIMS ages; Ray and Wanless 1980;Krogh and Clark 1987;Annesley et al 1992Annesley et al , 2005Hamilton and Delaney 2000;Rayner et al 2005). The cover sequence was described as a Paleoproterozoic syn-rift passive margin and foreland metasedimentary basin (Ansdell et al 2000;Tran et al 2003Tran et al , 2008 that is divided into Lower and Upper subgroups, separated by a regional unconformity (Tran 2001).…”

“…Previous studies of the Trans-Hudson Orogen have used geochemical, isotopic, and geochronological data to characterize the evolution of the Paleoproterozoic sedimentary and magmatic assemblages, including the Wollaston Group and underlying basement rocks (Ray and Wanless 1980;Bickford et al 1990;Annesley et al 1992Annesley et al , 2005Ansdell et al 2000;Rayner et al 2005;Tran et al 2008). The studies showed that the Paleoproterozoic mafic and felsic intrusive rocks record variable degrees of contamination by Archean and older Paleoproterozoic crust, underlining the complex evolutionary history of crust along the western margin of the Trans-Hudson Orogen.…”

“…A P-T path for the Wollaston pelitic gneisses has been determined based on detailed metamorphic equilibria, and defines a partial melting zone at depth and an emplacement path that is consistent with prograde near-peak metamorphic conditions of 6-9 kbar and ~750 °C (Annesley et al 2005). The U-Pb age (c. 1800 Ma) and relatively high-T partial melting conditions (~750 °C) confine the origin of the pegmatitegenerating melts to syn-to post-deformational events of the Trans-Hudson Orogeny.…”