GEOLOGICAL SETTING, PETROGRAPHIC AND GEOCHEMICAL CHARACTERISTICS OF THE CRETACEOUS AND TERTIARY IGNEOUS ROCKS IN THE HEKIMHAN HASANCELEBI AREA, NORTH-WEST MALATYA, TURKEY

Abstract

Upper Cretaceous to Tertiary igneous rocks outcrop in the Hekimhan-Hasancelebi area, about 80 km to the north-west of Malatya, Central-Eastern Anatolia. These igneous rocks consist of Maastrichtian Bahcedam volcanics, the Palaeocene(?) Hasancelebi pluton and the Neogene Yamadag volcanics. These latter rocks are subdivided into, from bottom to top, the Karadag volcanics, Leylekdag volcanics and Kocasar volcanics. The Hasancelebi pluton consists mainly of syenite, quartz syenite, monzonite and quartz monzonite. According to chemical criteria, the Hasancelebi pluton is classified as an alkaline oversaturated subtype of the cafemic association with a felsic I-type character. Some trace element data indicate an apparent within-plate origin. The Bahcedam volcanics are made up of tephrite basanite, basalts, trachybasalt and basaltic trachyandesite with an alkaline character. Other trace element criteria indicate both an arc and within-plate origin. Mid-ocean ridge basalt normalized distribution patterns of some incompatible elements indicate some conspicuous enrichment in the concentrations of K, Rb, Ba, Th and Nb; a slight enrichment in Zr; and some depletion in Sr, P and Ti. The Karadag volcanics are composed mainly of alkaline trachyandesites. The Leylekdag and Kocasar volcanics consist essentially of calc-alkaline andesitic rocks. Some trace element discrimination diagrams reveal a possible arc origin for both sets of volcanics. The Hasancelebi pluton is assumed to be part of the Cretaceous-Palaeogene Central-Eastern Anatolian alkaline province. The Leylekdag and Kocasar volcanics can be considered to be collision-related igneous rocks by taking into account the regional tectonic regime in Central-Eastern Anatolia. However, their trace element discrimination patterns indicate an arc origin. It is suggested that a study of the absolute age dates, rare earth element determinations and isotope geochemistry would lead to a better understanding of the tectonomagmatic evolution of this area.