Canada's craton: A bottoms-up view

Abstract

The origin of mantle lithosphere underlying Archean crustal provinces is most consistent with depletion at low pressures in the spinel facies under degrees of melting higher than observed in modern ocean basins. Depleted sections of the lithosphere created in convergent margin settings were underthrust and stacked to build a thick root with time. Geochronologic and geologic evidence can be interpreted to show that the final formation and amalgamation of the bulk of the "mantle root" occurs 0.5-1 b.y. later than the age of lithosphere from which it is comprised. "Silica enrichment" is not ubiquitous in the mantle beneath Archean crustal provinces. Where it does occur, it may he a heterogeneous feature possibly imparted by marine weathering of peridotite on the Archean ocean floor before it was stacked to form a mantle root.