A review of the “Tethyan” belt between Yugoslavia and Oman shows that metamorphic rocks, up to the amphibolite facies, occur at the base of many of the allochthonous ophiolite sheets. Although these rocks have generally been interpreted as slivers of older metamorphic basement, we argue for their formation by metamorphism of the tectonically overridden Mesozoic sedimentary and volcanic sequences during ophiolite emplacement. Metamorphism at a high structural level is indicated by the absence of high pressure assemblages.
Both frictional heating and the residual heat of thermally immature oceanic crust are theoretically capable of producing amphibolite facies temperatures. Where “old” oceanic crust has been emplaced, frictional heating is likely to dominate, but residual heat may be more important during emplacement of “young,” thermally immature crust. Implications for the geotectonic settings of specific Tethyan ophiolites are mentioned.