Displaced terranes and mountain building.

Numerous oceanic rises, several of which are submerged continental fragments, are embedded in the earth's oceanic plates and are fated to be consumed at active margins in the future. Some of these buoyant rises are presently being consumed, causing gaps in active volcanic chains, disordering the normal seismic pattern associated with subduction of oceanic crust, emplacing ophiolites, and possibly creating marginal seas. Some past oceanic rises have become accreted terranes, now found in ancient active margins. We suggest that some of these accreted, or allochthonous terranes resulted from the break-up of Gondwana and led to the growth by accretion of other continents. From Permian fragments in S Europe to present Arabia and Somalia, a host of continental slivers, microcontinents, and related rises have migrated from Gondwana to be accreted into Europe and Asia. Orogenic deformation has resulted, well before full continent-continent collision took place. Numerous accreted continental and noncontinental rises have been identified also in the Cordillera of W North America, Alaska, E Siberia, Japan and SE Asia also involving extensive orogenic deformation, ususally without full continent-continent collision. Many of these Pacific terranes have migrated across open oceans, coming from older continental masses. One possible source is Pacifica, an extension of Gondwana beyond New Zealand and Australia. -from Authors