RELATIONSHIP BETWEEN SLAB RETREAT AND MID-OCEAN RIDGE OUTPUT: PACIFIC BASIN

The Pacific basin is surrounded by retreating subduction zones and continental keels. As a subducting slab rolls back it forces the viscous mantle to move laterally resulting in high and low pressure, in confined areas such as the Pacific Basin we would expect to see high pressure. Both the subducting slabs and the continental keels are continuing to close in on the Pacific Basin, effectively shrinking the box thus increasing the pressure because the mantle within that box is largely confined. The mantle may exit through one or more of these tectonic settings; oceanic spreading centers, slab windows, or hotspots in the Pacific Plate. To determine if slab rollback and thereby the increased mantle pressure could be responsible for ridge and/or hotspot output, the volumetric output at the Pacific mid-ocean ridge and the volumetric change of the confined Pacific Basin were calculated for the past 15 million years. The comparison between ridge output and volume change of Pacific Basin will imply one of three different scenarios: (1) output of ridge is greater than the volume change of the basin suggesting a deep source of material extruded; (2) output of ridge is approximately equal to volume change indicating equilibrium between mantle and ridge processes with no contribution to horizontal mantle flow; (3) output of ridge is less than the volume change of the basin implying that mantle must escape through slab windows and hotspots.