Geochemistry and tectonic significance of metamorphic sole rocks beneath the Beysehir-Hoyran ophiolite (SW-Turkey)

The Beysehir-Hoyran ophiolite is situated in the western part of the Tauride belt (SW Turkey) and crops out at two localities north of the take Beysehir. It mainly comprises harzburgitic peridotites that were tectonically emplaced to their present position during the Late Eocene. The ophiolites themselves are tectonically overlain by either slope basin deposits with lava blocks (Egirler formation) or massive Triassic limestone blocks (Deliktas formation). High-grade sub-ophiolitic metamorphic rocks, i.e. epidote amphibolite, amphibolite, and pyroxene amphibolite, together with minor quartzite and calcschist, are observed at the base of the ophiolite sequence, where they occur as thin tectonic slices with an inverted metamorphic gradient. Average P-Tconditions of 630-770 degrees C and c. 6 +/- 1.5 kbar are calculated for the metamorphism of the amphibolites by conventional geothermobarometty, corresponding to a burial depth of 18-20 km. Both the sub-ophiolitic metamorphic rocks and the overlying mantle tectonites were intruded by isolated tholeiitic (Nb/Y = 0.041-0.108) diabase dikes, which do not transect the tectonic contact between the two units. Geochemical investigations of the amphibolites of the sub-ophiolitic rock suite show two different geochemical affinities, with the first group being alkaline in character (Nb/Y= 1-3.86) and the second one being tholeiitic (Nb/Y=0.064-0.13). REE patterns, trace element plots and tectonomagmatic discrimination diagrams indicate that the most probable protoliths for alkaline amphibolites are within-plate type alkali basalts, whereas those of the tholeiitic group resemble tholeiitic island arc basalts. Similarities between the geochemical characteristics of the amphibolites and those of the volcanic rocks of the Egirler fort-nation strongly suggest that the latter are the protoliths of the amphibolites. (c) 2007 Elsevier B.V. All rights reserved.