Tectonothermal Evolution of the Northern Minto Block, Superior Province, Quebec, Canada

Abstract

Previously considered one of Earth's largest granulite terranes, the Minto block, in northern Quebec, consists dominantly of granitic rocks with sparse supracrustal remnants that record low-pressure, high-temperature metamorphism to the amphibolite and granulite facies at ca. 2.7 Ga. Much of the region is underlain by plutonic rocks, including igneous charnockitic bodies, that provide little evidence of metamorphism. In contrast, pelitic assemblages in low-grade greenstone belts and their higher-grade shoulders define four metamorphic zones: 1) sub-staurolite-grade slates, found only in the Duquet belt, 2) staurolite -andalusite -sillimanite -garnet-zone schists, present in all belts, 3) marginal garnet -sillimanite ± kyanite migmatites, and 4) garnetsillimanite ± cordierite and garnet -orthopyroxene granulites, as enclaves within plutonic units. A prograde low-pressure, hightemperature regional facies-series is defined by andalusite -sillimanite assemblages, thermobarometric analyses that indicate peak conditions ranging from 3 kbar, 560°C to 8.4 kbar, 840°C, and short segments of anticlockwise P-T trajectories preserved in two of the lowest-grade areas. Kyanite occurs in migmatites in the vicinity of a ca. 2.81 Ga shear zone bounding two distinct supracrustal assemblages and marks an earlier Barrovian event. All belts are polydeformed, with a common, broadly synmetamorphic, NNW-striking, steep foliation and down-dip lineation related to regional-scale F 2 folds. Distributed late-metamorphic dip-slip shear appears responsible in some areas for cross-strike juxtaposition of low-and high-grade metamorphic zones. Older, generally poorly preserved D 1 deformation, recognized in several belts, may represent accretionary structures. Variably developed younger deformation includes NNW dextral transcurrent brittle-ductile shear zones (S 3 ), variably developed east-trending F 4 folds, and WNW-striking pseudotachylite zones. U-Pb monazite ages of 2702 Ma date high-grade metamorphism of a pelitic granulite, crystallization of two diatexites, and staurolite-zone metamorphism in one schist. Together with similar zircon ages of crust-derived granites, these data point to a major collisional orogeny at this time. Older titanite (2748-2765 Ma) indicates areas that escaped >650°C metamorphism during the 2.7 Ga event. Younger monazite occurs in a migmatite-grade rock (2688, 2672 Ma) and staurolite-zone schists (2679( -2642( , 2648( , 2637( , and 2642( -2628, similar to titanite ages in greenstones (2643-2550 Ma) and 40 Ar/ 39 Ar hornblende ages (2.64-2.56 Ga). These post-peak metamorphic ages in the greenstone belts based on monazite and titanite are attributed to hydrothermal growth from fluids channeled along permeable zones; they may reflect late reheating events observed throughout the Superior Province as leucogranitic magmatism, metamorphism in the deep crust, and mineral growth in shear zones. SOMMAIRELe socle de Minto, dans le nord du Québec, considéré antérieurement comme un des plus vastes terrains de roches transformé...

Age and isotopic geochemical characteristics of Archean carbonatites and alkaline rocks of the Baltic shield

“…According to the first model, the synformal structure of the Minto Block resulted from bilateral subduction beneath the Mesoarchaean crust [Percival et al, 1992Percival, Skulski, 2000]. The second model is based on the data from sapphirine-bearing xenoliths in the enderbite of the Minto granulite complex, which suggests a pressure between 7.5 and 14 kbar (24-46 km) and a very high temperature (755-1260 °C).…”

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

“…Firstly, the mineralogical assemblage recorded in the xenolith we have studied suggests burial of supracrustal belts to great depths (with a maximum pressure of 14 kbar), greatly extending the range of P-Tconditions for the Minto (maximum 8.4 kbar) obtained from other barometers (Percival & Skulski 2000, Bédard 2002. Either the early history of cratonization in the northern Superior Province is marked by significant crustal thickening, as advocated by Percival et al (1992Percival et al ( , 1994Percival et al ( , 2001), or some mechanism existed to allow supracrustal fragments to founder to such depths, perhaps through partial convective overturn (referred to as 'sagduction' by others) as suggested by Collins et al (1998) and Bédard et al (2002).…”

“…Sur la carte magnétique régionale, les complexes de Troie et de Qimussinguat dessinent des massifs circulaires plurikilométriques (Madore et al, 1999 Percival et Skulski, 2000) vs verticale (Bédard, 2002).…”

“…L'objectif principal de cette thèse est de déterminer l'évolution métamorphique de la De plus, l'analyse géothermobarométrique a pour objectif d'éclaircir le dilemme existant entre l'école de la tectonique horizontale Percival et Skulski, 2000) vs celle de la tectonique verticale (Bédard, 2002). Localisation des régions étudiées dans la Province du Supérieur (modifiée de Percival et al, 1992).…”

“…3.1), is principally composed of Archean felsic plutonic rocks in which are embedded numerous supracrustal slivers or belts (Percival et al 1997a). The supracrustal rocks are generally metamorphosed to the amphibolite or granulite grade, with rare preservation of greenschist assemblages in the cores of the largest belts (Percival & Skulski 2000). Amphibolite-grade belts are typically associated with hornblende-biotite tonalités, trondhj emites, granodiorites and granites, while granulite-grade belts are generally surrounded by enderbitic plutons.…”