Plagioclase Lherzolite-Residual Mantle Relationships within Two Eastern Mediterranean Ophiolites

The ophiolites of Othris, northern Greece, and Troodos, Cyprus, are of mixed lherzolite-harzburgite and harzburgite sub-type respectively. Within both ophiolites an entire spectrum of harzburgite, plagioclase harzburgite, lhcrzolite and plagioclase lherzolite interpreted respectively as residual and highly, moderately and slightly modified upper mantle has been recognised. Plagioclase lherzolite frequently contains gabbroic segregations generated by partial melting and incomplete extraction. Othris shows the full range of mantle peridotites while Troodos is dominated by harzburgite with very minor occurrences of plagioclase harzburgite and lherzolite. Chemically, the plagioclase lherzolites have low contents of the basaltophillic minor elements, and a composition slightly more residual than postulated upper mantle compositions, suggestive of a preceding phase of minor depletion. The Othris and Troodos ophiolites seem to have formed under fundamentally different environments --Othris as a marginal ophiolite at the inception on rifting of continental crust, and Troodos later in such an event when spreading was well established.