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

PLATE tectonics provides the basis far the interpretation of most current terrestrial tectonic activity, and is widely accepted as having been active over much of the Earth's history(1). Yet the timing of initiation of this process is subject to debate(2-9). So far, the earliest seismic evidence for plate tectonics has come from a fossil mantle suture in the Svecofennian orogen (1.89 Gyr ago)(10) and from inferred plate 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 construction of the continental crust(12-15). Here we present seismic data from a collision zone in the Superior Province of Canada, involving the Abitibi granite-greenstone Subprovince and the plutonic, are-related Opatica belt. We interpret dipping seismic reflections that extend 30 km into the mantle as representing a relict 2.69-Gyr-old suture associated with subduction. Although crustal structure, lithospheric thicknesses and convergence rates may have differed from those seen today, these seismic data provide direct evidence that plate tectonics was active in late Archaean times, 800 Myr earlier than indicated by previous seismic reflection surveys.