A review of the Superior Province of the Canadian Shield, a product of Archean accretion

Abstract

The Superior Province consists of northern and southern high-grade gneiss subprovinces and a central region of alternating granite-greenstone and metasedimentary belts. Subprovinces are commonly fault-bounded and display contrasting lithological assemblages, metamorphic and structural styles, geophysical characteristics, and ages; they are comparable to Phanerozoic suspect terranes. The Middle and Late Archean rocks of the Superior Province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca. 3.1 Ga. High-grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal-rich belts but one, Minnesota River Valley, is part of an older, ca. 3.6 Ga terrane that was juxtaposed late in the tectonic history. Granite-greenstone terranes are characterized by low-grade volcano-sedimentary sequences (tholeiitic-komatiitic submarine lava plain; tholeiitic-calc-alkalic submarine to subaerial central complexes; early platform-type quartz arenite-stromatolitic carbonate; late Timiskaming-type shoshonitic/alkalic volcanic-fluvial sediment) that range in age from ca. 3.0 Ga to 2.7 Ga. The volcanics represent oceanic, island arc, and continental arc volcanism, the quartz arenite-carbonate sequences deposition on relatively stable, early-formed ca. 3.0 Ga crust, and the Timiskaming-type sequences deposition in pull-apart basins developed along strike-slip faults. Late Archean, ca. 2.75-2.70 Ga greenstone sequences occur throughout the Superior Province. Middle Archean, ca. 3.0-2.8 Ga sequences are common in northern and central Superior province, rare or absent in the south. Volcanism was accompanied by mafic to trondhjemitic plutonism. The metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca. 3.0 Ga to 2.7 Ga. The metasediments were deposited after major volcanism and probably represent accretionary prisms. Late Archean orogenesis, accompanied and followed by calc-alkalic plutonism, youngs southward from about 2.73-2.72 Ga to 2.70-2.68 Ga. It involved large-scale north-south compression and dextral transpression and displays thin- to thick-skinned transitions. The contemporaneity of events along the lengths of the belts and their southward younging, coupled with the evidence of major compression, are consistent with subduction-driven oblique accretion of oceanic and continental volcanic arcs, accretionary sedimentary wedges, older microcontinental fragments etc. in a convergent margin setting analogous to parts of the Pacific Rim. Differences (eg. abundance of komatiites and tonalitic plutonic suites) are attributable to a hotter Archean mantle.