Turkish Journal of Earth SciencesTectono-Magmatic Evolution of Alkaline Volcanics at the Kırka-Afyon-Isparta Structural Trend, Sw Turkey
Dokuz Eylül Üniversitesi, Jeoloji Müh. Bölümü, Bornova, İzmir-TURKEY
Abstract: The youngest Alpine magmatism (Miocene to Quaternary) in Western and Central Anatolia is represented by three coeval assemblages from West to East. They are the Western Anatolian Volcanic assemblage (WAV), the N-S trending Kirka-Afyon-Isparta Alkaline Volcanic assemblage (KAIAV) and the Central Anatolian Volcanic Provinces (CAVP). The WAV and CAVP start with calc-alka-line volcanics and continue after Middle Miocene with shoshonitic to alkaline products of graben volcanism, while the KAIAV are all alkaline in character, without any former or later calc-alkaline contributions. The KAIAV are emplaced in three steps of alkaline vol-canic activities which exhibit southward younging along the N-S Kirka-Afyon-Isparta Structural Trend (KAIST). These three periods from N to S are represented by the Kirka (21-17 Ma), Afyon (14-8 Ma) and Isparta (4.7-4.0 Ma) alkaline rocks. In all of these local-ities volcanic evolutions begin similarly with a rhyolitic-trachytic main part (potassic 'K') and are followed by high-potassic (HK) or ultra-potassic (UK) dykes and domes. The KAIAV along the KAIST represents a fault controlled border zone between Western and Central Anatolia, where the WAV and the CAVP are located, respectively. Additionally the same fault system (KAIST) is also valid as a border zone between the Hellenic Arc (HA) and Cyprus Arc (CA) systems. The oblique character of this fault system (normal fault + strike slip component) is well known. Therefore, the KAIST is herein interpreted as a transform fault system between the HA and the CA. The KAIST separates also two allocthonous crystalline massifs of Anatolia, i.e. Menderes and Kırşehir massifs located in Western and Central Anatolia, respectively. It may also indicate the important role of the subductional-postcollisional tectonic regimes related to the metamorphic (core complex) areas involving former calc-alkaline volcanics of the WAV and the CAVP. The KAIAV along the KAIST are charac-terised by the absence of the calc-alkaline period, and indicate a different tectonic regime and source material than those of the WAV and the CAVP. The KAIST is an en echelon, oblique fault system with normal and strike-slip (dextral) periods. The last dextral period overlapped temporarily with the Isparta volcanics where the blocks of the Anatolian plate (and also Afyon volcanics) were pushed to the north over a stable magma source. This magma source could be considered either as a fixed hot spot or plume on the intersection point of two main fault systems. The N-S emplacement of plum material along the KAIST may also be considered as an other alter-native mechanism of southwards younging of the KAIAV. The tectonic periods before and after the production of the Isparta vol-canics are represented by graben and half-graben systems. They seem like fertile and sterile periods of volcanic activities over the transform fault systems of the KAIST between the HA and the CA. While the normal faulting periods represent the sterile areas, the change to dextral movements resulted in small decompressions in the mantle and gave rise to the production of alkaline (K, HK, UK) volcanics, which are also observable in the latest stage of the WAV.
Key Words: Potassic-Ultra Potassic Volcanism, Alkaline Volcanics, Tranform Fault.
Turkish J. Earth Sci., 7, (1998), 201-214.
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