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The late Neoproterozoic-early Palaeozoic extension along the West African craton and the Peri-Gondwanan terranes |
1 Natural History Museum, Mineralogy–Petrography Division, MTA, 06520, Ankara, Turkey (e-mail: semihgursu{at}yahoo.com)
2 Department of Geological Engineering, Middle East Technical University, 06531, Ankara, Turkey
In western Turkey, Late Neoproterozoic basement rocks are represented by variably deformed metasedimentary and meta-igneous rocks within different tectonostratigraphical units that make up the Alpine Tauride–Anatolide Platform. In the Kütahya–Bolkar Dag
unit to the NE of Afyon this basement mainly includes garnet-bearing mica schists intruded by metamorphic granitic rocks with relict porphyritic textures. The youngest zircon ages obtained from the granitic rocks by the single zircon evaporation method are 542±5.0 Ma on average, which correlate with the Late Pan-African–Cadomian granitic magmatism. The granitic rocks are rhyodacitic or dacitic and peraluminous in composition, and display geochemical characteristics of I-type (tonalite–trondhjemite–granodiorite (TTG) source) felsic intrusive rocks. Trace and rare earth element patterns with distinct depletion in Rb, K, Nb, Sr, P and Ti relative to the other trace elements correlate very well with a Proterozoic TTG source. The petrogenetic modelling also implies that they were developed by partial melting of a TTG source by 20% fractional melting plus 20% Rayleigh fractional crystallization. The emplacement temperatures estimated by using zircon (790–820 °C), apatite and monazite saturation thermometry are about 827–1035 °C; these are in accordance with I-type rather than S-type granite melts. A geochemical comparison of the NE Afyon granitic rocks with the coeval quartz-porphyries in the Sandikli area of the Geyik Dag tectonic unit suggests that the latter may represent the more evolved felsic part of the Cadomian magmatism. Hence, both basement complexes are parts of the same Gondwanan terrane and represent the eastern continuation of the North African–Southern European terrane assemblage.
