Application of the detachment model to reconstruction of conjugate passive margins

The detachment ("simple-shear') model of continental extension predicts that opposing passive-margin pairs are asymmetrical. This results in two broad classes of passive margins - upper-plate margins in the hanging wall of the detachment, and lower-plate margins in the footwall. The detachment model applied here incorporates pure-shear extension above and below the master detachment, and ramp-flat geometry for the detachment. The detachment model is applied to the United States Atlantic-northwest Africa and the southern Australia-Antarctica margin pairs in some detail, and to the southern and northern Atlantic Oceans, the Tasman Sea margins and the Provencal basin in lesser detail. The model supports the view that at least some of the magnetic quiet zones (MQZ) that occur oceanward of many passive margins consist largely of highly extended, metamorphosed and underplated (intruded) continental crust rather than oceanic crust. -from Authors