ACCRETION OF ARCHEAN OCEANIC PLATEAU FRAGMENTS IN THE ABITIBI GREENSTONE-BELT, CANADA

The arc-arc collision model is often applied to the evolution of Archean greenstone belts. This model predicts concordant stratigraphic relations among the various lithologies evolving generally from komatiitic-tholeiitic affinities toward calc-alkalic affinities. New geological data from the Malartic composite block of the Abitibi greenstone belt indicate that this volcanic pile, rather than representing a conformable sequence, is composed of four distinct mafic lithotectonic domains that are overlain by a calc-alkalic sequence. The mafic domains are thought to be examples of accreted Archean oceanic plateau material that were deformed during their collage state. The younger calc-alkalic sequence represents extension-related volcanism that erupted through the accreted and deformed plateau material, possibly as a consequence of ridge subduction ir a regime of oblique convergence. The relations described here may represent a common feature of Archean terranes.