A synthesis of electromagnetic studies in the Lithoprobe Alberta Basement Transect: constraints on Paleoproterozoic indentation tectonics

Abstract

Electromagnetic surveys of the crust and upper mantle underlying the Western Canada Sedimentary Basin have revealed two conductivity anomalies that are arguably related to Paleoproterozoic tectonic processes, recording a signature diagnostic of euxinic (foreland?) basin succession and perhaps defining a deep-marine transtensional basin. As well, a regionally pervasive electrical anisotropy throughout the crust crosses Proterozoic tectonic boundaries and is aligned in many areas with the regional tectonic fabric (as expressed by aeromagnetic data) created during the final stages of Proterozoic tectonic assembly of western Laurentia. There is also an order of magnitude increase in the upper mantle conductivity underlying Churchill Province Archean crust relative to that underlying the neighbouring Proterozoic crust. The interpretations of the electromagnetic observations are analogous with the Tertiary to modern-day tectonic development of southeast Asia. The foreland basin succession would reflect the closing of the South China Sea and the deep-marine basin may be analogous to the Andaman Sea and North Sumatra basin. Electrical anisotropy may be indicative of the successive lateral accretion of oceanic crust beneath the continental shelf followed by shortening. The enhanced mantle conductivity mechanism is unknown, although it may be associated with metasomatic modification of the subcontinental lithosphere subsequent to collisional thickening and followed by delamination or convective removal of some lithosphere. While the Indo-Eurasian–Laurentia tectonic analogy is incomplete, it is sufficiently compelling in explaining the electromagnetic and other data that it is a useful basis for understanding the Proterozoic assembly of Laurentia.