Obduction processes in ancient, modern and future ophiolites

Abstract

Geologic and tectonic processes of ophiolite obduction deduced from structural mapping, timing of deformation and metamorphism and palinspastic reconstruction of ancient ophiolite complexes compare closely with modern processes operative in the western Pacific. Many ongoing arguments about the origin of ophiolite complexes (oceanic, island arc or marginal basin) and their emplacement (subduction-related or not) are largely semantic and depend on exactly what individuals regard as island arcs, marginal basins or subduction zones. A review of tectonic processes currently active in the western Pacific region shows a wide range in size, shape and duration of arcbasin complexes and some of these show uniformitarian models similar to those proposed for emplacement of ancient ophiolites. The Tethyan ophiolites of the Semail (Oman Mountains) and Spontang (Western Himalaya of Ladakh-Zanskar) and the Ordovician western Newfoundland ophiolites are compared with recent examples of the Mariana basin, Yap trench, Banda arc, Luzon arc and Papua New Guinea. It is concluded that they are all connected in some way with marginal basins and island arcs in varying stages of development and maturity. Emplacement of these ophiolites is related to continental underthrusting of a trapped marginal basin and accretionary prism comparable to present-day examples of the N Australian margin underthrusting Timor and the Banda Sea and the SE China margin underthrusting the Luzon arc.