THE OPHIOLITE CONUNDRUM: TECTONIC SETTING FOR THE ORIGIN AND EMPLACEMENT WITH EMPHASIS ON OMAN

The Penrose definition of an ophiolite as a sequence of rocks that represents some type of oceanic lithosphere helped fill in the gaps of plate tectonic theory. Ophiolites provided a three dimensional exposure lacking in seafloor studies. The recognition of tectonite peridotite, e.g. Vourinos, as the basement for oceanic crust connected ophiolites to oceanic lithosphere. The mid-ocean ridge origin of ophiolites allowed for visualization of quasi-steady state processes that might occur as a result of plate tectonics. Ophiolites found in mountain belts were confirmation of the Wilson cycle. Ophiolitic suture zones marked ocean closing events. With great interest came inconsistencies in the simple picture; trace element abundances linked many ophiolites around the world to environments related to subduction, i.e. the suprasubduction zone model. Put simply do ophiolites primarily form in the hanging wall position of a subduction zone or do they form in the mid-ocean ridge-derived footwall position destined to be subducted? The term obduction was coined to describe ophiolites as those that escaped subduction by whatever process. “The tectonic conditions accompanying ophiolite emplacement remain unclear” (Moores, 1968) still holds today almost 50 years later. The Oman ophiolite represents one of the best studied complexes which despite many decades of study is still interpreted in the two fundamentally different ways. For Oman, obduction involved no suture, and secondly the same group of rocks occupied both footwall and hanging wall positions when the major plates changed motion vectors at about 100 Myr ago.