Chapter 13 Labrador Geosyncline: Type Example of early Proterozoic Cratonic Reactivation

Abstract

Abstract The Labrador Trough is the erosional remnant of an early Proterozoic geosyncline that formed by reactivation of an Archaean craton. Evolution of the geosyncline took place in seven phases: (1) development of a red-bed graben in the centre and south of the geosyncline; (2) slow subsidence and deposition of shelf sediments; (3) tectonic instability, faulting, erosional discordances, local basins of mass-flow conglomerate; (4) massive rapid subsidence, voluminous basalt volcanism, deposition of shale and greywacke; (5) restabilization, deposition of the shelf sequence of cycle II; (6) rapid subsidence, voluminous basalt volcanism and renewed deposition of shale and greywacke; (7) folding and metamorphism, subduction of the geosyncline below its hinterland. About 100–200 km of Archaean basement disappeared, probably by underplating, below the hinterland to the east of the trough. The author speculates that plate-tectonic processes, or processes closely related to plate tectonics, probably took place since the Archaean. Plate—margin geosynclines and island arc—forearc basin systems formed, perhaps, where the underflow of descending mantle convection currents acted upon oceanic crust and upon the ocean—continent interface. Ensialic belts like the Labrador Trough formed, perhaps, where the underflow of such convection cells acted upon continental crust, within a large sialic block.