Isotope geochemistry and geochronology of unusual granitoid and ophiolite bodies along the SE Anatolian orogen, Turkey

KARAOĞLAN F., PARLAK O., THÖNİ M., KLÖTZLİ U., KOLLER F.

Alpine Ophiolites and Modern Analogues Workshop, Parma, Italy, 30 September - 02 October 2009, pp.38-39

  • Publication Type: Conference Paper / Summary Text
  • City: Parma
  • Country: Italy
  • Page Numbers: pp.38-39
  • Çukurova University Affiliated: Yes

Abstract

The Southeast Anatolian Orogenic Belt (SAOB) records well-preserved remnants of mountain building processes along the Alpine-Himalayan system. The evolution of the SAOB initiated with closure of the Neotethyan Ocean, located between the Tauride platform to the north and Arabian platform to the south in late Cretaceous, and ceased by the continent-continent collision in Miocene. The tectono-magmatic/metamorphic units cropping out along the orogenic belt are key elements to better understand the evolution of the SAOB, which are located in Hatay-Kahramanmaras-Malatya-Elazig regions. These units are, structurally from top to bottom, a) metamorphic massifs, b) ophiolites, c) ophiolite-related metamorphic rocks and d) granitoids. The metamorphic massifs are represented by the Malatya, Keban, Bitlis and Puturge metamorphics. The ophiolites and related metamorphic units are characterized by the Göksun, İspendere, Kömürhan and Guleman ophiolites, and Berit metaophiolite. The field and geochemical evidence carried out on the SE Anatolian ophiolites may favor more than one SSZ spreading center above a north dipping subduction, namely the one between the Taurides and the Bitlis-Pütürge massif in which Göksun, Berit, İspendere, Kömürhan and Guleman ophiolites formed and the second one between the Bitlis-Pütürge massif and the Arabian platform in which Kızıldağ (Hatay), Koçali, Baer-Bassit and Troodos ophiolites formed in late Cretaceous. The ophiolites are tectonically overlain by the metamorphic massifs. The granitoids, which mark the Andean type active margin formation mainly in Late Cretaceous, crop out in three localities namely the Goksun, Dogansehir and Baskil regions. The temporal-spatial and genetic relations of these units determine geological framework of the Southeast Anatolian Orogenic Belt.

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.