During the last ten years significant concentrations of Pt and Pd (more than 1000 ppb Pt + Pd) have been reported from several ophiolite complexes including Shetland, Leka, Al 'Ays, Zambales, Ceruja and Thetford. Similar studies on others, including those in Cyprus and Oman, have failed to reveal equivalent concentrations. Here we compare the characteristics of these ophiolite sequences and propose that Pt- and Pd-rich ophiolites contain thick sulphur-bearing ultramafic crustal units that crystallized from PGE-rich boninitic magmas produced by excess partial melting in a water-rich subduction zone.

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