THE STRUCTURAL EVOLUTION OF OCEANIC CORE COMPLEXES: A CONCEPT BASED ON ANALOG MODELING

Abstract

Oceanic core complexes are lithological assemblages of predominantly peridotites and serpentinites, located along intersections of some slow-spreading oceanic accreting rifts and fracture zones, embedded in the predominantly basaltic oceanic lithosphere, and fresh and old basalts are juxtaposed across the fracture zone. Centrifuge-based experimental models indicated that subduction would initiate at sites where two lithospheric slabs are juxtaposed, provided that the density difference between them is at least 200 kg/m3 and the friction along their contact plane is low. It was discerned that the modeled underthrust denser lithosphere would reach the modeled asthenosphere and represent tectonic subduction. In many such occurrences, extension in the over-riding slab would develop normal faults that could be penetrated by the lighter fraction of the subducted slab, generating volcanism and diapirism. These experiments suggest further that since the density contrasts and the low friction constraints could be satisfied at the intersections of fracture zones and slow-spreading oceanic ridges, subduction could occur there too and not only along ocean-continent boundaries. Furthermore, since the thermal gradient in ridge-fracture zone intersections is very steep and volatiles in the underthrust slab abound in the subducted slab, a portion of the underthrust basalts would undergo serpentinization and another segment could become peridotitic. It is suggested further that the light serpentinite would ascend through the normal faults in the over-riding slab and reach the seafloor diapirically, carrying along large sections of peridotite, to produce the serpentinite-peridotite petrology that typifies oceanic core complex at junctions of fracture zones and slow spreading ridges.