Petrogenesis of Cenozoic mafic–ultramafic alkaline lavas from the Tigris volcanic field, NE Syria

Abstract

Mafic–ultramafic Quaternary lava flows form the Tigris volcanic field (covering 1750 km2) at the northeastern tip of Syria and extend into Turkey. This volcanic field occurs between the Euphrates graben and the Bitlis–Zagros collision suture that forms the boundary between the Arabian and Eurasian plates. The rocks are made up of labradorite, clinopyroxene, olivine and opaque phases. The Tigris lavas are compositionally restricted to basanites and alkali basalts, having a narrow range of major element compositions (SiO2, 42.2–48.2 wt%; MgO, 5.7–9.0 wt%, with Mg numbers ranging from 0.51 to 0.62; TiO2, 1.7–3.2 wt%), and are alkaline in nature. The rocks are enriched in HFS elements such as Zr (119–231 ppm), Nb (14–43 ppm) and Y (17–22 ppm). The REE patterns are strongly fractionated ((La/Yb)N= 10.6), indicative of a garnet-bearing source. The143Nd/144Nd isotopic compositions range from 0.512803 to 0.512908, and87Sr/86Sr from 0.70327 to 0.70403 (εNd= 3.2–5.3) suggesting strong affinities to ocean island basalts. Modelling using a variety of mantle source materials and different degrees of partial melting indicates that the magma was produced by a small degree of batch partial melting (F = 1.5%) of a primitive, garnet-lherzolite fertile mantle source. The overall petrological/chemical nature supports this interpretation. Shear heating at the base of the lithospheric mantle of the northern boundary of the Arabian plate, caused by a change in plate motion as the Arabian plate moved in a more easterly direction during the Plio-Quaternary, could represent a possible source of the heat necessary for partial fusion and magma generation. Adiabatic decompression and melting represents a more likely process for the generation of the Tigris magma. Elemental ratios such as K/P (4.6), La/Ta (12), La/Nb (0.90), Nb/Y (1.22) and Th/Nb (0.09) indicate that the magma was subjected to minimal crustal contamination.

Petrogenesis, geochemistry, and tectonic setting of a basaltic body within the Gercus Formation of northern Iraq: first record for Eocene anorogenic volcanic activity in the region

“…Plots of Ba -Ba/Zr (Figure 10a), Ba -Ba/Y ( Figure 10b), P 2 O 5 -P 2 O 5 /TiO 2 ( Figure 10c), P 2 O 5 /Al 2 O 3 -Zr/Al 2 O 3 ( Figure 10d (Figure 10f) showed positive linear correlations (r = 0.99, 0.99, 0.93, 0.49, 0.52, and 0.88, respectively); such trends indicate the significant role of partial melting processes in the production of the magma of the Gercus Basalt. Similar relations observed in the Syrian Tigris basalts were interpreted to be indicative of a fertile, garnet-lherzolite-bearing asthenospheric mantle (Abdel-Rahman and Lease, 2012), which could be the case for the Gercus Basalt. The presence of water-bearing minerals like amphibole or phlogopite in the upper mantle during partial melting causes retention of alkali elements such as K, Rb, Ba, and water relative to the melting of normal anhydrous minerals (Adam et al, 1993;LaTourrette et al, 1995;McCoy-West et al, 2010).…”

“…There are many volcanic fields in the southern part of Turkey located below the Bitlis suture, which is the Turkish counterpart of the Shalair-Sanandaj-Sirjan Suture of Iraq and Iran (Figure 1a), not very far from the study area, such as Karacalıdağ and Akçakale, which were interpreted to have been formed in rift-related extension zones (grabens) (Polat et al, 1997). These basalt fields of Quaternary age in Turkey as well as many others in neighboring Syria, such as the Quaternary Dijla basalts (Abdel-Rahman and Lease, 2012) and Euphrates basalts (Lease and Abdel-Rahman, 2008), have many characteristics similar to the Gercus Basalt. They are intraplate basanites and alkaline basalts, OIB-like, and share most of their petrographic and geochemical properties with the Gercus Basalt.…”

“…al., , 2012Kürkçüoğlu et al, 2015 ), Syria (Sharkov et al, 1994;Lustrino and Sharkov, 2006;Krienitz et. al., 2007;Lease and Abdel-Rahman, 2008;Ma et al, 2011;Abdel-Rahman and Lease, 2012), Iran (Azizi and Moinevaziri, 2009;Ahmadzadeh et al, 2010;Allen et. al., 2013;Torkian et al, 2016), Jordan (Shaw et al, 2003;El-Akhal, 2004;Yaseen, 2014), Lebanon (Abdel- Rahman and Nassar, 2004), and the CMACIP (Lustrino and Wilson, 2007).…”

“…The Syrian Quaternary Tigris and Euphrates basalts were probably generated by a small degree of partial melting of a primitive, garnet-lherzolite fertile mantle source (Lease and Abdel-Rahman, 2008; Abdel-Rahman and Lease, 2012). The ratios of highly incompatible to moderately compatible elements such as Ba/Y, Ba/Zr, and P 2 O 5 /TiO 2 decrease with increasing degrees of partial melting, which is considered to be the most efficient process for fractionating these elements (Pankhurst, 1977).…”

“…The ratios of highly incompatible to moderately compatible elements such as Ba/Y, Ba/Zr, and P 2 O 5 /TiO 2 decrease with increasing degrees of partial melting, which is considered to be the most efficient process for fractionating these elements (Pankhurst, 1977). The ratio of some other elements such as Zr, Nb, and Sr incompatible during melting to Al 2 O 3 , which is buffered by residual garnet, usually decreases systematically with increasing degrees of partial melting (Hoernle and Schmincke, 1993;Abdel-Rahman and Lease, 2012). Plots of Ba -Ba/Zr (Figure 10a), Ba -Ba/Y ( Figure 10b), P 2 O 5 -P 2 O 5 /TiO 2 ( Figure 10c), P 2 O 5 /Al 2 O 3 -Zr/Al 2 O 3 ( Figure 10d (Figure 10f) showed positive linear correlations (r = 0.99, 0.99, 0.93, 0.49, 0.52, and 0.88, respectively); such trends indicate the significant role of partial melting processes in the production of the magma of the Gercus Basalt.…”