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

Electromagnetic surveys of the crust and upper mantle underlying the Wester n Canada Sedimentary Basin have revealed two conductivity anomalies that ar e arguably related to Paleoproterozoic tectonic processes, recording a sign ature diagnostic of euxinic (foreland?) basin succession and perhaps defini ng a deep-marine transtensional basin. As well, a regionally pervasive elec trical anisotropy throughout the crust crosses Proterozoic tectonic boundar ies and is aligned in many areas with the regional tectonic fabric (as expr essed 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 Ar chean 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 for eland 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 Sumatr a basin. Electrical anisotropy may be indicative of the successive lateral accretion of oceanic crust beneath the continental shelf followed by shorte ning. The enhanced mantle conductivity mechanism is unknown, although it ma y be associated with metasomatic modification of the subcontinental lithosp here subsequent to collisional thickening and followed by delamination or c onvective removal of some lithosphere. While the Indo-Eurasian-Laurentia te ctonic analogy is incomplete, it is sufficiently compelling in explaining t he electromagnetic and other data that it is a useful basis for understandi ng the Proterozoic assembly of Laurentia.