Petrogenesis and the evolution of Pliocene Timar basalts in the east of Lake Van, Eastern Anatolia, Turkey: A consequence of the partial melting of a metasomatized spinel–rich lithospheric mantle source

Highlights

• The post-collisional Pliocene Timar basalts in the Turkish-Iranian high plateau.

• The Geochemical and geochronological features of the Timar basalts.

• The partial melting of a metasomatized spinel–rich lithospheric mantle source.

• The EC-AFC modelling for the Pliocene Timar basalts.

Abstract

The Eastern Anatolian region provides a good example for collision–related volcanic activity. This activity started during the Middle Miocene and continued through the Pliocene and Quaternary. The new K − Ar ages reveal that the post–collisional Pliocene Timar basalts located in the East Anatolian Accretionary Complex (EAAC) erupted between 4.72 (Zanclean) and 3.29–2.93 Ma (Piacenzian). The Pliocene Timar basalts consist of plagioclase, clinopyroxene (augite), and olivine minerals and have glomeroporphyritic, intergranular, and ophitic textures. They display enrichment in light rare earth elements (LREEs) with (La/Yb)_N values that range between 3.19 and 6.66 to 21.63–5.61. ⁸⁷Sr/⁸⁶Sr(i) and ¹⁴³Nd/¹⁴⁴Nd(i) isotopic ratios of the Timar basalts are 0.70599–0.70436 and 0.51277–0.51259, respectively. The εNd(t) values of these rocks range between 1.0116 and 1.0121. ⁸⁷Sr/⁸⁶Sr(i) and Nd(t) contents indicate crustal contamination during the emplacement of the Timar basalts. According to the Energy Constrained–Assimilation Fractional Crystallization (EC–AFC) model, this contamination rate is between ~1.4 and 4.4%. The melting model shows that the least evolved samples of the Timar basalts were formed by ~0.1–2% partial melting of the lherzolitic source. Primitive melts that constituent Timar basalts were occurred with partial melting of a magma source that has predominantly spinel bearing mineralogy. All data indicate that the origin of the parental melts of the Timar basalts is metasomatized lithospheric mantle source and then these melts reached the surface from the fissures that is related to extensional tectonics in Pliocene.

Introduction

Continental collision zones are interesting regions because they contain different volcanic rock types. Collision–related volcanic rocks can occur as a result of crustal over–thickening, extensional collapse, regional lithospheric delamination, slab break–off, and plume–related mechanisms in these areas (Pearce et al., 1990; Davies and Von Blanckenburg, 1995; Keskin et al., 1998). Therefore, collision zones in the world can contain different rock types ranging from basalt to rhyolite. The most common rock type in these varieties is basalt, and it is important for constraining composition, structure, and the evolution history of the mantle and its dynamics.

The Eastern Anatolia Region is a very special area in terms of volcanism and volcanic rocks which is related to the collision. This region, which is formed by consequent crustal shortening and thickening with the collision between Arabian and Eurasian plates along the Bitlis–Zagros suture zone, is a high plateau with an average elevation of 1.5 km (Yılmaz et al., 1998; Şengör et al., 2003, 2008; Barazangi et al., 2006). The Eastern Anatolian High Plateau (EAHP) has generated with a collision between Arabian and Eurasian plate along the Bitlis–Zagros suture zone in the Late Oligocene to Early Miocene (Okay et al., 2010; Karaoğlan et al., 2016; Oyan, 2018a; Açlan and Altun, 2018; Açlan and Duruk, 2018) (Fig. 1). Şengör et al. (2003, 2008) proposed that the basement of the East Anatolia occurred from the accretionary complex (EAAC). Topuz et al. (2007) pointed out that the accretionary complex does not reflect the crust of the region and that the Eastern Anatolian plateau should construct over a continental basement.

Volcanic activities following collision between Arabian-Eurasian plates began at the Middle Miocene (~15 Ma; Lebedev et al., 2010) in the Eastern Anatolian region and intensified during the Pliocene and Quaternary (Oyan et al., 2017). Previous studies on the collision-related volcanics in East Anatolia revealed that these volcanics vary from tholeiitic to calc–alkaline types (Innocenti et al., 1976, 1980; Pearce et al., 1990; Yılmaz, Y., 1990; Yılmaz et al., 1998; Ercan et al., 1990; Keskin, 2003, 2007; Keskin et al., 2006; Özdemir et al., 2006; Şengör et al., 2008; Özdemir and Güleç, 2014; Özdemir, 2016; Oyan et al., 2016, 2017; Açlan and Turgut, 2017; Oyan, 2018b; Özdemir et al., 2019).

There is a limited number of studies suggesting that the source of Quaternary basaltic volcanism in the region is primitive magma (Oyan et al., 2017; Özdemir et al., 2019). Timar basaltic volcanism can be considered as part of the basaltic plateau sequence described by Oyan et al. (2016) and can be observed in large areas north of Lake Van. However, Oyan et al. (2016) obtained the geochemical analysis of only four samples and isotopic analysis of one sample from the Timar basalts. Therefore, determining the geochemical and isotopic components of these lavas is important to understanding both the evolutionary processes and mantle source areas of the Pliocene basaltic volcanism. This petrological study on Timar basaltic volcanism will give important clues for a better understanding of the geodynamic and petrogenetic processes during the Pliocene period in this part of the region.

The main aim of this study is to determine the geological and geochemical magma source characteristics and evolution of the Timar basalts. This paper deals in detail with the age of volcanic eruption in the east of Lake Van, Eastern Anatolia, Turkey based on K − Ar ages.