40Ar-39Ar geochronology and petrogenesis of postcollisional trachytic volcanism along the İzmir-Ankara-Erzincan Suture Zone (NE, Turkey)*

Abstract

The obliteration of the Neo-Tethyan Ocean and collision of the microplates along the northern part of Turkey led to the development of the İzmir-Ankara-Erzincan suture zone (IAESZ). After the collision of Pontides with the Central-Anatolian Crystalline Complex (CACC) in the Paleocene, a new phase of extension and volcanism concomitantly developed along the northern (Almus; Pontides) and southern (Yıldızeli; CACC) sides and along the IAESZ during the Middle Eocene time interval. The first products of the Middle Eocene volcanism in these areas are represented by calc-alkaline to alkaline (basic-intermediate) volcanic and volcanoclastic units together with late-stage trachytic dikes, plugs, and stocks. The mantle source area of both volcanic units displays a metasomatized character, which was dominantly fluxed by sediment-sourced melts. The partial melting of the metasomatized source area gave rise to first-stage basic-intermediate volcanism in the crustal levels. Simultaneously with the generation of the first-stage volcanism, basaltic trachyandesitic shallow-seated magma mushes were also developed. The reactivation of these shallow-seated mushes by latestage extensional tectonics gave rise to the development of trachytic volcanism in both regions, which have a high-K to shoshonitic character. Almus trachytic lavas are phenocryst-poor and have differentiated Mg# numbers (avg. 26). On the other hand, Yıldızeli trachytic lavas have a broad compositional range (benmoreite to latite); they are phenocryst-rich and show more basic character (Mg# avg. 40). Trachytic volcanism in both areas is largely controlled by fractional crystallization of similar basaltic trachyandesitic parental magma with minor assimilation of the upper crustal lithologies. 40 Ar-39 Ar ages from sanidine phenocrysts from both areas also confirm that trachytic volcanism in both regions developed nearly coevally in different tectonic blocks (~41-40 Ma). Generation of similar volcanism on the different tectonic blocks during the postcollisional stage was probably governed by a regional-scale delamination and/ or lithospheric removal-related tectonomagmatic processes.

İzmir-Ankara-Erzincan Sütur Zonu (KD, Türkiye) Boyunca Gelişen Çarpışma Sonrası Orta Eosen Magmatizmasının Volkano-Stratigrafik Olarak Araştırılması

“…Additionally, distinct geochemical features of the middle Eocene volcanic rocks such as alkalinity (Keskin et al, 2008) is not related with the deep sourced asthenospheric melts since these lavas display low Mg# contents; low Ni (ppm) with highly fractionated geochemical patterns (Göçmengil et al, 2017;. Hence recent publication of Göçmengil et al (2018) suggest that the first and second stage volcanic episode of Almus and Yıldızeli regions might be related with melting of metasomatized peridotitic mantle in lithospheric depths.…”

“…After the development of the more anhydrous mineral rich volcanic units; volcanism shift towards the more acidic members by the presence of trachyte and trachyandesite dykes, plugs and stocks and these products marks the final manifestations of the volcanism for both regions. This late stage pulse can be accounted for the more silica rich, assimilation and fractional crystallization induced magmatism in the eastern part of the Pontides (Arslan et al, 2013;Yücel et al, 2014;Temizel et al, 2016, Göçmengil et al, 2018.…”

“…However, Yıldızdağ magmatic units are heterogenous in cm to mm scale with cumulate settling and common occurance of the hydrous minerals contradicts with direct melting origin from the upper mantle. Thus, generation of the gabbroic intrusion probably generated by melting of water rich magma source areas which contain amphibole, phlogopite in varying degrees which is suggested for middle Eocene volcanic units by Göçmengil et al, (2018).…”

“…(Akçay and Beyazpirinç, 2017). On the other hand, recent publication by Göçmengil et al, (2018) display 40-41 M.a. for the trachytic lavas in Almus and Yıldızeli regions.…”

“…Trachyte dikes and plugs are widely distributed eastern part of the study area (Göçmengil et al, 2018). They are generally NW-SE/NE-SW oriented at the northern part and W-E oriented at the southern part of the study area.…”