ARCHEAN SUBDUCTION INFERRED FROM SEISMIC IMAGES OF A MANTLE SUTURE INTHE SUPERIOR PROVINCE

PLATE tectonics provides the basis far the interpretation of most curr ent terrestrial tectonic activity, and is widely accepted as having be en active over much of the Earth's history(1). Yet the timing of initi ation of this process is subject to debate(2-9). So far, the earliest seismic evidence for plate tectonics has come from a fossil mantle sut ure in the Svecofennian orogen (1.89 Gyr ago)(10) and from inferred pl ate convergence, subduction and accretion in the Trans-Hudson orogen ( 1.91-1.79 Gyr ago)(11). As yet, seismic data from Archaean areas have been able to demonstrate only the importance of compression in the con struction of the continental crust(12-15). Here we present seismic dat a from a collision zone in the Superior Province of Canada, involving the Abitibi granite-greenstone Subprovince and the plutonic, are-relat ed Opatica belt. We interpret dipping seismic reflections that extend 30 km into the mantle as representing a relict 2.69-Gyr-old suture ass ociated with subduction. Although crustal structure, lithospheric thic knesses and convergence rates may have differed from those seen today, these seismic data provide direct evidence that plate tectonics was a ctive in late Archaean times, 800 Myr earlier than indicated by previo us seismic reflection surveys.