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Department of Geology, West Virginia University, Morgantown, West Virginia 26506, USA
Integration of data from field, geochemistry, and radiometric age investigations of the active Banda arc—Australia collision zone (Banda orogen) and the Jurassic Brooks Range ophiolite provide new constraints for the origin and emplacement of Oman-type ophiolites. These ophiolites are characterized by ultramafic residuals and mafic products that are chemically modified by various degrees of partial melting. The internal structure of the igneous complexes document acute extensional strains. A high temperature metamorphic sole with some continental margin protoliths are locally preserved at the structural base of the massifs. Age relations between the ophiolites, their metamorphic sole, and collisional mountains in which they reside indicate important temporal and spatial associations. Some of these relations are inconsistent with ophiolite genesis in intra-oceanic settings.
Formation of the Savu and Weber basins around the active Banda orogen provide modern analogues of peri-collision extensional processes. These extensional domains are transitional between zones of active supra-subduction zone magmatism (ophiolite genesis) and low-angle overthrusting (ophiolite emplacement). Geochemical data from the volcanic basement of the Savu basin are similar to ‘transitional-type’ ophiolite volcanic suites. Ar/Ar ages, and stratigraphic and structural data from the basin indicate volcanism and forearc extension coincide in time and space with initial collision between promontories of the NW Australian passive margin and the Java trench, suggesting a link between the two processes. Similar age and stratigraphic relations are also documented in the Brooks Range and other Oman-type ophiolites.
Peri-collisional extension opens small SSZ ocean basins that may be obducted during or shortly after they form by progressive convergence at multi-plate boundaries. These processes provide a self-perpetuating mechanism for ophiolite genesis and emplacement that accounts for both the similar and diverse aspects of many ophiolites.
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