Geochronology and geochemistry of Eocene-aged volcanic rocks around the Bafra (Samsun, N Turkey) area: Constraints for the interaction of lithospheric mantle and crustal melts

Abstract

International audience40Ar-39Ar age, whole-rock chemical and Sr-Nd isotope data are presented for the post-collisional, Eocene (51.3-44.1 Ma)-aged volcanic rocks from the Bafra (Samsun) area in the western part of the Eastern Pontides (N Turkey) aiming to unravel their sources and evolutionary history. The studied Eocene volcanic rocks can be divided into two groups: analcime-bearing (tephritic lava flows and dykes) and analcime-free (basaltic to trachytic lava flows and basaltic dykes). The analcime-bearing volcanic rocks have a fine-grained porphyritic texture with clinopyroxene phenocrysts, whereas analcime-free volcanic rocks show a variety of textures including hyalo-microlitic microgranular porphyritic, intersertal, trachytic, fluidal and glomeroporphyritic. The volcanic rocks also show evidence of mineral-melt disequilibrium textures such as sieved, rounded and corroded plagioclases, partially melted and dissolved clinopyroxenes and poikilitic texture. Petrochemically, the parental magmas of the volcanic rocks evolved from alkaline to calc-alkaline lava suites and include high-K and shoshonitic compositions. They display enrichments in light rare earth and large ion lithophile elements such as Sr, K and Rb, as well as depletions in high field strength elements such as Nb, Ta, Zr and Ti, resembling subduction-related magmas. The analcime-bearing and -free volcanic rocks share similar incompatible element ratios and chondrite-normalised rare rearth element patterns, indicating that they originated from similar sources. They also have relatively low to moderate initial 87Sr/86Sr (0.7042 to 0.7051), high positive εNd(t) values (+ 0.20 to + 3.32), and depleted mantle Nd model ages (TDM1 = 0.63-0.93 Ga, TDM2 = 0.58–0.84 Ga). The bulk-rock chemical and Sr-Nd isotope features as well as the high Rb/Y and Th/Zr, but low Nb/Zr and Nb/Y ratios, indicate that the volcanic rocks were derived from a lithospheric mantle source that had been metasomatised by slab-derived fluids. Trace element modelling suggests that the parental magma(s) of the volcanic rocks represent mixtures of melts derived by low-degree (~ 5–10 %) partial melting of spinel-lherzolite (40–85%) and garnet-lherzolite (15–60 %) mantle sources. Sr-Nd isotopic modelling also suggests that a 25–35% lower crustal component was added in the parental magmas; AFC modelling additionally indicates minor upper crustal contamination during the evolution of the volcanic rocks. In conclusion, integration of the geochemical, petrologic and isotopic data with regional geology suggests that the analcime-bearing and -free volcanic rocks evolved from parental magma(s) derived from melts of a subcontinental lithospheric mantle and lower crustal sources

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

“…Different hypotheses have been suggested for the generation of the Early Cenozoic magmatism along our study areas and surrounding regions (Central and Eastern Pontides) such as slab break-off (Keskin et al, 2008), delamination (Arslan et al, 2013;Temizel et al, 2016) Göçmengil et al (2017). Assimilant values are taken from Köksal et al (2013) thickening and melting of continental crust (Topuz et al, 2005), and direct generation by a subducting lithospheric slab (Eyuboglu et al, 2016).…”

“…Thus, we suggest that the trace element ratios/plots used for understanding of the evolution of the arc magmatism can also be reliable tools to investigate the presence and behavior of sedimentary melts/fluids, subduction components in mantle source areas of postcollisional magmatics. (Gülmez et al, 2013;Kasapoğlu et al, 2016) and middle Eocene volcanics from the Eastern Pontides (Kaygusuz et al, 2011;Temizel et al, 2012Temizel et al, , 2016Arslan et al, 2013;Aslan et al, 2014;Yücel et al, 2017) are also plotted. Data for lithospheric mantle array and MORB from Wilson (1989) and Gill (1981).…”

“…Petrological evolution of some portion of these rocks is explained by postcollisional delamination-governed tectonomagmatic processes together with assimilation-related modifications (Temizel et al, 2016;Yücel et al, 2017). However, the generation of coevally developed trachytic units along the other parts of the IAESZ is poorly documented and the petrogenesis of these units needs to be clarified.…”

“…The vanishing of the northern branch of the Neo-Tethyan ocean during the Cretaceous and subsequent collision of the Pontides and Anatolide-Tauride microcontinents with the CACC in the Paleocene gave rise to a long and narrow ophiolitic mélange belt called the IAESZ at the northern part of the Anatolian Plate (Şengör and Yılmaz, 1981;Okay and Tüysüz, 1999) (Figure 1a). Around both sides and along this suture zone, postcollisional Eocene magmatism (particularly Middle Eocene) developed through the western to eastern part of the Anatolian Plate and is represented by granitoids (Harris et al, 1994;Genç and Yılmaz, 1997;Topuz et al, 2005;Arslan and Aslan, 2006;Okay and Satır, 2006;Karslı et al, 2007Karslı et al, , 2011Boztuğ, 2008;Karacık et al, 2008;Ustaömer et al, 2009;Altunkaynak et al, 2012;Gülmez et al, 2013;Öztürk, 2015, Özdamar et al 2017), gabbroic intrusions (Boztuğ et al, 1998;Temizel et al, 2014;Eyuboglu et al, 2016), and calcalkaline, mildly alkaline, and potassic/shoshonitic volcanic products (Figure 1b;Peccerillo and Taylor, 1976;Keskin et al, 2008 and references therein; Karslı et al, 2011, Kaygusuz et al, 2011Arslan et al, 2013 and references therein; Aydınçakır and Şen, 2013;Dokuz et al, 2013;Gülmez et al, 2013;Aslan et al, 2014;Aydınçakır, 2014, Sipahi et al, 2014Yücel et al, 2014;Kasapoğlu et al, 2016;Temizel et al, 2016).…”

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

“…The vanishing of the Northern branch of the NeoTethyan ocean in Cretaceous and subsequent collision of the Pontides and Anatolide-Tauride micro-continents (together with Central Anatolian Crystalline Complex: (CACC)) in Paleocene give rise to a long and narrow suture zone called İzmir-Ankara-Erzincan (IAESZ) at the northern part of the Anatolian Plate (Şengör and Yılmaz 1981;Okay and Tüysüz 1999) (Figure 1a). Around both sides and along this suture zone, post-collisional Eocene magmatism developed through western to eastern part of the Anatolian Plate and represented by granitoids (Harris et al, 1994;Topuz et al, 2005;Arslan and Aslan 2006;Okay and Satır 2006;Karslı et al, 2007Karslı et al, , 2012Boztuğ., 2008;Karacık et al, 2008;Ustaömer et al, 2009;Altunkaynak et al, 2012;Gülmez et al, 2013;Kaygusuz and Öztürk 2015) gabbroic intrusions (Boztuğ et al, 1998;Temizel et al, 2014;Eyüboğlu et al, 2016) and calc-alkaline, mildly alkaline and shoshonitic volcanic products (Figure 1b;Peccerillo and Taylor 1975;Ercan et al, 1998;Keskin et al, 2008 and references therein; Karslı et al, 2011, Kaygusuz et al, 2011Aydınçakır and Şen 2013;Arslan et al, 2013 and references therein; Dokuz et al, 2013;Gülmez et al, 2013;Aslan et al, 2014;Aydınçakır, 2014;Sipahi et al, 2014;Yücel et al, 2014;Kasapoğlu et al, 2016;Temizel et al, 2016…”