Complete metamorphic cycle and long‐lived anatexis in the c. 2.1 Ga Mistinibi Complex, Canada

Abstract

Secular changes in the architecture, thermal state, and metamorphic style of global orogens are thought to have occurred since the Archean; however, despite widespread research, the driving mechanisms for such changes remain unclear. The Paleoproterozoic may prove to be a key era for investigating secular changes in global orogens, as it marks the earliest stage of an eon that saw the onset of modern‐style global tectonics. The 2.1 Ga granulite‐facies Mistinibi‐Raude Domain (MRD), located in the Southeastern Churchill Province, Canada, offers a rare exposure of Paleoproterozoic high metamorphic grade supracrustal sequences (Mistinibi Complex, MC). Rocks from this domain were subjected to petrochronological investigations to establish P–T–t–X evolutions and to provide first order thermal state, burial and exhumation rates, and metamorphic gradients for the transient Paleoproterozoic times. To obtain comprehensive insight into the P–T–t–X evolution of the MRD, we used multi‐method geochronology—Lu–Hf on garnet and U–Pb on zircon and monazite—integrated with detailed petrography, trace element chemistry, and phase equilibria modelling. Despite the extensive use of zircon and monazite as geochronometers, their behaviour in anatectic conditions is complex, leading to substantial ambiguity in interpreting the timing of prograde metamorphism. Our results indicate a clockwise metamorphic path involving significant melt extraction from the metasedimentary rocks, followed by cooling from >815°C to ~770°C at ~0.8 GPa. The timing of prograde burial and cooling from supra‐ to subsolidus conditions is constrained through garnet, monazite, and zircon petrochronology at 2,150–2,120 Ma and at 2,070–2,080 Ma, respectively. These results highlight long‐lived residence of the rocks at mid‐crustal supra‐solidus conditions (55–70 Ma), with preserved prograde and retrograde supra‐solidus monazite and zircon. The rocks record extremely slow burial rates (0.25–0.30 km/Ma) along a high metamorphic gradient (900–1,000°C/GPa), which appears symptomatic of Paleoproterozoic orogens. The MC did not record any significant metamorphism after 2,067 Ma, despite having collided with terranes that record high‐grade metamorphism during the major 1.9–1.8 Ga Trans‐Hudson orogeny. The MC would therefore represent a remnant of a local early Paleoproterozoic metamorphic infrastructure, later preserved as superstructure in the large hot Trans‐Hudson orogen.

Lu–Hf garnet dating and the timing of collisions: Palaeoproterozoic accretionary tectonics revealed in the Southeastern Churchill Province, Trans‐Hudson Orogen, Canada

“…(2020), (b) Godet, Guilmette, Labrousse, Davis, et al. (2020), (c) Charette et al. (2021), (d) Kelly et al., (2011), (e) This study (see Table 4).…”

“…Data from the New Quebec Orogen are from (Boon & Hynes, 1990; Godet, Guilmette, Labrousse, Smit, et al., 2020; Henrique‐Pinto et al., 2017; James & Dunning, 2000; Rayner et al., 2017; Van der Leeden et al., 1990; Wardle et al., 2002). The Archean to Palaeoproterozoic crustal blocks that compose the Core Zone follow the redefinition of (Corrigan et al., 2018) namely the George River Domain (Charette et al, 2018; Corrigan et al., 2018; Martelain et al., 1998), Mistinibi‐Raude Domain (Charette et al., 2019; Corrigan et al., 2018; Godet, Guilmette, Labrousse, Davis, et al., 2020), and the Falcoz River Block (Charette et al., 2021; Corrigan et al., 2018; Lafrance et al, 2015, 2016). Data from the Lac Lomier Complex are from Charette et al.…”

“…Although it is accepted that all the crustal blocks and cratons have their own tectonothermal histories (e.g. Corrigan et al., 2018; Godet, Guilmette, Labrousse, Davis, et al., 2020; Godet, Guilmette, Labrousse, Smit, et al., 2020), the precise timing of their assembly remains largely unaddressed. Recent integrated petrochronological studies (Charette et al., 2021; Godet, Guilmette, Labrousse, Davis, et al., 2020; Godet, Guilmette, Labrousse, Smit, et al., 2020) have revealed diachronous metamorphism across the strike of the CZ and New Quebec Orogen (NQO).…”

“…Corrigan et al., 2018; Godet, Guilmette, Labrousse, Davis, et al., 2020; Godet, Guilmette, Labrousse, Smit, et al., 2020), the precise timing of their assembly remains largely unaddressed. Recent integrated petrochronological studies (Charette et al., 2021; Godet, Guilmette, Labrousse, Davis, et al., 2020; Godet, Guilmette, Labrousse, Smit, et al., 2020) have revealed diachronous metamorphism across the strike of the CZ and New Quebec Orogen (NQO). However, such constraints are missing in the central part of the Torngat Orogen and the westernmost units of the North Atlantic Craton, and the timing for the onset of collision and granulite facies metamorphism in this region remain poorly constrained.…”

Metamorphic Conditions of Neotethyan Meliatic Accretionary Wedge Estimated by Thermodynamic Modelling and Geothermobarometry (Inner Western Carpathians)

“…The metabasite set is a part of the new HPx-eos thermodynamic models introduced in 2016 [37]. It has since been used and tested by several authors, e.g., [38][39][40][41]. Thermobarometry is very challenging, and a special Chlorite-Mica database was developed for low-grade metamorphic rocks lacking indexing minerals [42][43][44].…”