The tectonic evolution of Thelon tectonic zone, Canada: a new model based on petrological modeling linked with Lu-Hf garnet and U-Pb accessory mineral geochronology

Abstract

Petrological modeling and geochronology (Lu-Hf garnet, U-Pb monazite, zircon and titanite) for seven mid-amphibolite to granulite-facies metamorphic rocks in the Thelon tectonic zone (Ttz) provide new insights into its orogenc evolution. A Grt-Sp-Sil diatexite records 2.01-2.00 Ga garnet and monazite growth during >830oC contact metamorphism associated with voluminous convergent margin plutonism. The most widespread, 1.96–1.90 Ga metamorphism is associated with clockwise P-T paths, indicating it was driven by crustal thickening. Earlier (1.96–1.92 Ga) and lower temperature (630 -730 oC; 6-8 kbar) metamorphism in the eastern Slave craton contrast with ~860 oC (7.5 kbar), 1.91–1.90 Ga diatexites in the central, Paleoproterozoic plutonic rock-dominated, core of the Ttz. These differences are interpreted to reflect lower versus upper plate settings, respectively. A contribution of mantle heat is suggested by the counter-clockwise P-T path and 885 oC (5.7 kbar) conditions recorded by diatexite associated with c. 1.9 Ga peraluminous leucogranite that dominates a corridor along the Ttz – Rae craton boundary. A tectonic model is proposed wherein the Ttz evolved at an accretionary margin after rifting of Ttz microcontinent (mTtz) off the Rae craton at c. 2.2–2.1 Ga. Voluminous plutonism at 2.01 – 1.98 Ga formed via east-dipping subduction under mTtz. Following 1.97 Ga collision of the Slave craton and mTtz, west-dipping subduction generated 1.96–1.95 Ga plutonism in the composite mTtz-Slave upper plate. Collision of Rae craton at 1.95–1.94 Ga led to crustal thickening, widespread 1.91-1.90 Ga high-grade metamorphism and extensive crustal melting in the central Ttz.