SUBDUCTION INITIATION AT PASSIVE MARGINS - THE SCOTIAN BASIN, EASTERNCANADA AS A POTENTIAL EXAMPLE

Thermal evolution modeling based on the geometry of the Scotian Basin, eastern Canada, and analysis of the shear resistance associated with lithospheric faulting are used to investigate the initiation of subduc tion at passive margins. Previous studies have demonstrated the diffic ulty of subduction initiation at mature passive margins. However, uniq ue features along a passive margin may facilitate subduction initiatio n. Subduction may initiate along a part of the margin (1) by extension al or strike-slip deformation rather than shortening, (2) by deformati on of the weaker continental lithosphere rather than oceanic lithosphe re, (3) by heating and weakening of oceanic lithosphere due to lateral heat transfer from adjacent continental lithosphere, and (4) by heati ng and weakening of the lithosphere due to the passage of a mantle plu me beneath the margin. The values of shear resistance under these cond itions are still higher than those calculated for ridge push, indicati ng that subduction initiation at passive margins is difficult even wit h these weakening mechanisms. However, pulses of compression associate d with plate reorganization may be enough to trigger subduction at suc h passive margins.