A regional perspective of the Quetico metasedimentary belt, Superior Province, Canada

Abstract

Alternating greenstone-granite and metasedimentary gneiss belts are a first-order tectonic feature of the southem Superior Province. The tectonic development of the Quetico metasedimentary belt is reviewed with regard to depositional, structural, and metamorphic-plutonic history. Over its 1200 km length, the belt consists of marginal metasedimentary schists of turbiditic origin and interior metasedimentary migmatite and peraluminous leucogranite. Polyphase deformation has resulted in a steep easterly-striking foliation and regional, gently east-plunging stretching lineation. Metamorphic grade varies in a low-P facies series from greenschist at the belt margins to upper amphibolite and local granulite in the central rnigmatiteintrusive granite zone. Mineral assemblages in the central zone yield estimates of metamorphic pressure that increase systematically eastward over 800 km from about 250 MPa (2.5 kbar) near the Canada -United States border to 600 MPa (6 kbar) in granulites adjacent to the Kapuskasing structural zone.Geochronology suggests that sediments were deposited at approximately the same time as active volcanism in adjacent volcanic belts, although evidence of volcanic -sedimentary stratigraphic contiguity is weak as a result of later transcurrent movement parallel to major lithological boundaries. Adjacent belts are inferred to have been contiguous since common D, deformation, 2689-2684 Ma ago. Major plutonism and associated metamorphism occurred in the Quetico Belt approximately 2670-2650 Ma ago, significantly later than major plutonism in the adjacent volcanic belts.The linear disposition of greywacke-rich sediments over 1200 krn invites an analogy with modem accretionary prisms.However, the high-temperature, low-pressure metamorphism of the Quetico Belt is inconsistent with such a low-heat-flow environment, and a change in tectonic-regime would be required to account for the metamorphism and intracrustal plutonism. Simple cessation of subduction beneath the thick sedimentary prism could have led to restoration of isotherms, with possible attendant crustal melting and isostatic recovely.L'altemance de zones de roches vertes -granites et de gneiss mktas6dimentaires dans le sud de la province du lac SupCrieur constitue un trait tectonique de premier ordre. L'histoire tectonique de la ceinture metastdimentaire de Quetico est dinterpdtC en regard des Cvknements saimentaires, structuraux et mCtamorphiques-plutoniques. Cette zone, d'une longueur de 1200 km, est bordke de schistes mktaddimentaires d'origine turbiditique et dont l'intkrieur est occupC par des migmatites mBtas6dimentaires et des leucogranites peralumineux. Une orogenkse polyphaske a crCC une foliation de direction est avec pendage subvertical et une linkation d'ktirement avec faible plongCe vers l'est. Dans une sequence de faciks de basse pression, le degd de mttamorphisme varie des schistes verts, en bordure de la zone, B des amphibolites supCrieures et granulites locales, dans le centre de la zone oil se trouvent les migmatites et les intrus...

Great Lakes tectonic zone in Marquette area, Michigan: Implications for Archean tectonics in north-central United States

“…Deformation D2 in this area occurred between 2,689+3/-2 Ma and 2,684+6/-3 Ma, similar to the age suggested by Davis and others (1989) for D2 in the Rainy Lake wrench zone. These ages are compatible with the less precise isotopic ages on rocks in northern Minnesota and Michigan (Peterman, 1979), and it seems probable that the rocks and structures throughout the Wawa and Quetico subprovinces are approximately coeval (Percival, 1989). Although convergence along the GLTZ undoubtedly was diachronous, collision probably occurred in the approximate interval 2,692-2,686 Ma (Davis and others, 1989).…”

Formation and evolution of granite magmas from migmatites :

“…Based on the similarity of rock types and sedimentary features, Percival (1989) suggested that the Quetico, Nemiscau, Opinaca and Ashuanipi subprovinces ( Fig. 1 (Percival & Sullivan 1988;Davis et al 1990;Fralick & Davies 1999;Zaleski et al 1999).…”

“…Simplified geological map of the Superior province modified from Percival (1989) showing the location of the Ashuanipi subprovince at the eastern end of the Opmaca, Nemiscau and Quetico line of metasedimentary belts.…”

“…Peak metamorphic temperatures increase from west to east along the Quetico, Nemiscau, Opinaca and Ashuanipi subprovinces, which Percival (1989) linked to a systematic tilting of the Superior province that exposes deeper crastal levels in the east.…”

“…Percival (1989), Lapointe (1996) and Doyon (2004). Therefore, since only the Quetico metasediments are presently well characterized (Sawyer 1986 and unpublished data) they will be used as the protolith composition for the Ashuanipi.…”