Andean-type active margin formation in the eastern Taurides: Geochemical and geochronogical evidence from the Baskil granitoid (Elazig, SE Turkey)

Abstract

The Southeast Anatolian Orogen resulted from collision of the Afro-Arabian and the Eurasian plates following the Cretaceous to Miocene closure of the southern Neotethyan oceanic basin. In this orogenic belt, there are number of tectonomagmatic/stratigraphic units in the Kahramanmaras-Malatya-Elazig region that are important to understand the geological evolution of southeast Anatolia during the Late Cretaceous. These are (a) metamorphic massifs (i.e. Malatya-Keban platform), (b) ophiolites (i.e. Goksun, Ispendere, Komurhan), (c) ophiolite-related metamorphics (i.e. Berit metaophiolite) and (d) granitoids (i.e. Goksun, Dogansehir and Baskil). The Baskil granitoid crops out to the northwest of Elazig and is a large magmatic body (170 km(2)) that intruded all of the above-mentioned units during Late Cretaceous time.

The Baskil granitoid comprises both mafic and felsic plutonic/sub-plutonic rock associations. The felsic plutonic phase includes granite, granodiorite, tonalite and quartz monzonite whereas the felsic sub-plutonic phase is characterized by aplite, granophyre, granite porphyry and granodiorite porphyry. The granite and granodiorite contain mafic microgranular enclaves (MME). The mafic plutonic phase comprises gabbro, diorite, quartz diorite. whereas the mafic sub-plutonic phase is represented by diabase, microdiorite, quartz microdiorite, diorite porphyry, quartz diorite porphyry and dykes of orbicular gabbro dyke. Geochemically, the Baskil granitoid rocks have I-type, metaluminous-peraluminous calc-alkaline characteristics. The REE-and ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, together with biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The Ar-40/Ar-39 geochronology of the granitoid rocks yielded biotite ages of 81.9 +/- 0.7 Ma and 81.5 +/- 0.8 Ma (95% confidence level). Coexisting hornblende. and hornblende from additional samples, yielded ages ranging from 84.0 +/- 0.7 Ma to 81.5 +/- 1.1 Ma. The ophiolites are believed to have formed in a suprasubduction zone tectonic setting, whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or later-stage thrusting (similar to 90 Ma). These units were then thrust beneath the Malatya-Keban platform during the progressive closure of the southern Neotethys. This was followed by intrusion of the granitoids (85-82 Ma) along the Tauride active continental margin of the southern Neotethys. (C) 2008 Elsevier B.V. All rights reserved.