Brøgger Seminar Series
The Ophiolite Paradox
by Professor Emeritus John Dewey, University College, Oxford 

When? 15 October, 15h00 | Where? Högbomsalen, Geovetenskapens hus


The “ophiolite enigma, paradox or conundrum” is that obducted, large-slab, full-sequence ophiolite complexes originated by organized sea-floor spreading (e.g. sheeted dyke complexes) and indicates an origin at oceanic ridges, yet have geochemical affinities that link them to arcs, especially fore-arcs. Ophiolites sensu lato originate in a variety of ways in several unusual tectonic environments. None represent obducted sheets from the young oceanic crust and mantle of large oceans. This presentation will explore the ‘ophiolite paradox’ by looking at a variety of examples.

The Jurassic Balkan and Greek ophiolites were obducted from the floors of young narrow oceans, and the Alpine-type ophiolites represent the strongly attenuated floors of rifts and "extreme" para-rifts in which stretched subcontinental mantle, and associated mafic plutonics and volcanics, are caught up in suture zones during shortening and inversion. Seamounts, plateaux, and fracture zones are clipped off subducting oceanic plates as mafic ophiolite scraps in slices and melanges. The classic full ophiolite complexes from harzburgite, through gabbro and sheeted complex, to pillow basalt, which occur in giant obducted slabs, are of Ordovician or Cretaceous age and formed in supra-subduction zone environments in continent-facing arcs that were soon after obducted onto the adjacent rifted continental margin. Ophiolites cannot be thought of as simple random records of opening, widening, narrowing, and closing of oceans associated with the Wilson Cycle, but are events related to particular and special tectonic configurations.



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