THE PETROLOGY OF THE ORTAKOY DISTRICT AND ITS OPHIOLITE AT THE WESTERN EDGE OF THE MIDDLE ANATOLIAN MASSIF, TURKEY

The geological history of a regionally metamorphosed sequence of Silur ian or early Devonian sediments, now calcite marbles, quartzites, semi pelitic, psammitic and migmatitic gneisses containing K-feldspar, sill imanite, and garnet with later andalusite and cordierite, is outlined with chemical analyses of the rocks and minerals, the latter suggestin g peak metamorphic conditions about 600 to 700 degrees C at 4kb. Depos ition was in part at an active continental margin and in part probably ata passive margin and was followed by basic intrusions, now amphibol ites. Later gabbroic rocks are shown for the first time by their geoch emistry, especially REE, to be probably part of a major ophiolite shee t, tectonically emplaced and containing late magmatic or metamorphic h ornblende. Later intrusive hornblende diorite, with appinitic (diorite dykes with voluminous euhedral hornblende) and calc-alkaline lamproph yric affinites, immediately preceded the intrusion of voluminous grani toids (granite, tonalite, quartz monzonite) of probably late Cretaceou s to Palaeocene age, whose geochemistry indicates a continental volcan ic are setting. Neogene formations completed the rock sequence.