Abstract

An outstanding problem with understanding the origin and significance of many ophiolites is reconciling their are geochemical signatures with the structural evidence for extreme crustal extension. A hypothesis is presented that accounts for these and other ophiolite characteristics by processes that are kinematically linked to ophiolite emplacement. Ophiolite emplacement, particularly over passive continental margins, is probably due to intra-oceanic subduction dipping away from the continent where the future ophiolite is the subduction hanging wall. If the continent-bearing plate is kinematically linked to the plate behind the subduction-related arc, with a limiting case in which the continent and the rear-arc oceanic plate are mutually stationary, then supra-subduction-zone spreading may accommodate the resultant subduction hinge retreat that proceeds at the subduction rate. Thus, extreme extension in an arc petrotectonic environment during ophiolite generation could produce the unique structure and geochemistry of ophiolites due to the plate geometry that prescribes their emplacement onto continental margins. The kinematic link between the continent-bearing plate and the rear-arc plate could be due to both plates being a single large plate, both plates being large plates that move independently of the intervening ophiolitic microplate, or viscous drag beneath the continent-bearing plate.

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