Alpine Ophiolites and Modern Analogues Workshop, Parma, Italy, 30 September - 02 October 2009, pp.38-39
The ophiolite-related metamorphic units are exhumed evidences of advancing subduction. Metamorphic units are composed of greenschist, amphibolite and granulite facies rocks and non-metamorphosed ultramafic rocks, cumulate gabbro and isotropic gabbro parts of an ophiolitic sequence. The initial 87Sr/86Sr ratios of the ophiolite-related metamorphic rocks vary between 0.70286 and 0.70321, whereas the initial 143Nd/144Nd ratios vary between 0.51297 and 0.51299 corresponding to εNdT values of +7.7 to +8.1. The age of the peak metamorphism is measured as 50.1±3.2 Ma from garnet + pyroxene pairs in the granulite facies rocks. The calculated P-T conditions of these rocks indicate 700-750 °C and 12-13 kbar. The An content of plagioclases around the pyroxenes in granulite facies rocks are low for basic rocks, indicating the breakdown of pyroxenes and Na transmission to plagioclases. This may be occurred during the exhumation of the metamorphic units. The initial (calculated on the basis of relative U-Pb zircon ages) 87Sr/86Sr ratio of one sample from Dogansehir granitoid is 0.70389, whereas the initial 143Nd/144Nd ratio is 0.512720, corresponding to εNdT value of +2.3. The lower εNdT value may indicate a crustal contamination from lower crust. Four zircon ages measured from Dogansehir (Malatya) granitoid by LA-ICP-MS U-Pb vary from 43.2±1.6 to 48.8±0.8 Ma. These crystallization ages indicate that the subduction, which also led to the formation of the granitoids, was still progressing during Eocene time and the formation of the granitoid comprises more than one episodes.
The available geochemical and geochronological data suggests that metamorphism of the oceanic crust during intraoceanic subduction was still in progress during Eocene and reached its peak metamorphic conditions at about 30 km in depth. After exhumation of the metaophiolitic rocks, they were overlain by the metamorphic massifs in Eocene. All the units finally were subject to episodic intrusion of the granitic melts which were resulted by the subduction of the oceanic material and lower crust during middle Eocene.