Geochronological and kinematic constraints on crustal shortening and escape in a two-sided oblique-slip collisional and magmatic orogen, Paleoproterozoic Taltson magmatic zone, northeastern Alberta

Abstract

The southern Taltson magmatic zone (south of 60°N) is a composite continental magmatic arc and collisional orogen resulting from the convergence of the Buffalo Head terrane with the Archean Churchill craton. Taltson basement (ca. 3.2–3.0 Ga and 2.4–2.14 Ga) and Rutledge River supracrustal gneisses (2.13–2.09 Ga) were intruded by voluminous I- and S-type magmatic rocks between 1.99 and 1.92 Ga. Taltson magmatic zone was deformed by three ductile shear zones: Leland Lakes, Charles Lake, and Andrew Lake, exhibiting both strike- and dip-lineated mylonitic domains. Kinematic data for shear zones are reported at microscopic, mesoscopic, and macroscopic (remotely sensed data) scale. We present field and U–Pb isotopic data (zircon and monazite) for magmatic and metamorphic rocks that constrain the timing of granulite to upper amphibolite-grade shearing in the Leland Lakes and Charles Lake (formerly Allan) shear zones to ca. 1938–1934 Ma. Foreland (easterly) vergent thrusting on the Andrew Lake shear zone is ca. 1932 Ma. Taltson shear zones were overprinted by widespread amphibolite- to greenschist-grade shearing, which is constrained by published 40Ar–39Ar and K–Ar dates on hornblende and muscovite to between ca. 1900 and 1800 Ma. We propose a crustal architecture, resembling a crustal-scale asymmetric flower structure, in which the Charles Lakes shear zone formed the fundamental shear zone of a middle to lower crustal sinistral transpression system that accommodated southward escape of crust in the upper plate of an oblique continental subduction–collision zone, with shortening partitioned into synchronous outwardly vergent thrust systems to the east and west of the main shear zone.

The Origin of Laurentia: Rae Craton as the Backstop for Proto-Laurentian Amalgamation by Slab Suction

“…On the upper plate, subduction-related (including slab-breakoff ?) magmatism (2.03 -1.96 Ga) and associated hightemperature granulite-grade metamorphism switched around 1.96 Ga to anatectic magmatism (1.96 -1.91 Ga) and exhumation (Bostock et al 1987;James et al 1988;van Breemen and Henderson 1988;Thériault 1992;McDonough et al 2000). The Rae/Slave collision age estimate of 1.97 Ga, determined over 20 years ago, remains an excellent example of apparent consilience between lower and upper plate chronologies.…”

Magnetotelluric imaging of anisotropic crust near Fort McMurray, Alberta: implications for engineered geothermal system development

“…Weckmann et al 2003;Eaton et al 2004;Yin et al 2014). Geological studies of the exposed part of the CLsz by McDonough et al (2000) have mapped high-grade metamorphic mylonites that are strike-lineated in the centre of the shear zone, and dip-lineated to either side, similar to Model 1 in Fig. 11, and the most highly sheared portions of the CLsz appears on aeromagnetic surveys as a magnetic low, surrounded on either side by magnetic highs.…”

“…1). Approximately 150 km to the north are positive magnetic anomalies associated with elevated magnetite content (Sprenke et al 1986), which can be traced southward from granite and gneiss outcrops of the Charles Lake shear zone (CLsz) near Lake Athabasca (McDonough et al 2000).…”

Interprétation tectonométamorphique du nord de la province du Supérieur, Québec, Canada /

“…The more recent examples occurred during Paleoproterozoic (McDonough et al, 2000), Paleozoic (Nemes and al., 1997), Hercynian (Le Corre and Bouloton, 1987) and Cenozoic time (Cunningham et al, 1997). They have also been described in the Canadian Rockies and the French Alps.…”