Abstract

<p>Based on the volcanostratigraphic studies, zircon U-Pb dating and geochemical data, the Late Cretaceous volcanic rocks (LCVs) from the Artvin region in the eastern Sakarya zone (NE Turkey) consist of mafic/basaltic (S1-Çatak and S2-Çağlayan) and felsic/acidic (S1-Kızılkaya and S2-Tirebolu) rock types that occurred in two successive stages: (i) first stage (S1: Turonian to Early Santonian) and (ii) second stage (S2: Late Santonian to Campanian). In both stages, the basaltic rocks contain generally calcic plagioclase and lesser augite crystals, whereas the acidic samples commonly contain quartz, sodic plagioclase and K-sanidine phenocrysts. Data from clinopyroexene thermobarometry point to the S2-Çağlayan basaltic rocks having crystallised at higher temperatures and under deeper crustal conditions (T = 1128 ± 15 <sup>o</sup>C, P = 6.5 ± 0.7 kbar and D = 19.5 ± 2.1 km) than those of the S1-Çatak rocks (T = 1073 ± 11 <sup>o</sup>C, P = 2.2 ± 1.0 kbar, D = 6.6 ± 3.0 km).</p><p>The LCVs show a wide compositional spectrum, ranging from tholeiite to calc-alkaline/shoshonite and are typically represented by a geochemical composition resembling subduction-related arc rocks although the <sup>87</sup>Sr/<sup>86</sup>Sr<sub>(i)</sub> (0.7044–0.7071) and ɛNd<sub>(i)</sub> values (-0.63 to +3.47) as well as <sup>206</sup>Pb/<sup>204</sup>Pb<sub>(i)</sub> (18.07 to 18.56), <sup>207</sup>Pb/<sup>204</sup>Pb<sub>(i)</sub> (15.57 to 15.62) and <sup>208</sup>Pb/<sup>204</sup>Pb<sub>(i)</sub> (37.12 to 38.55) ratios show very limited variation. The average δ<sup>18</sup>O isotope values of the S1-Kızılkaya (5.3 ± 0.5‰) and S2-Tirebolu (4.9 ± 0.8‰) zircons are quite consistent with average mantle values (5.3 ± 0.3‰). The similar isotopic compositions of the studied mafic and felsic volcanic rocks, and the relatively high Mg# values (up to 0.4–0.51) of the felsic samples indicate a cogenetic origin. The parent magmas of the S1-Çatak and S2-Çağlayan mafic volcanic rocks were derived from underplated basaltic melts that originated by partial melting of metasomatised spinel lherzolite and spinel-garnet lherzolite, respectively. It is proposed that the compositions of the S1-Kızılkaya (mainly dacitic) and S2-Tirebolu (rhyolitic to trachytic) felsic rocks were particularly controlled by metasomatised mantle–crust interaction and MASH zone plus shallow crustal fractionation processes.</p><p>Our data, together with data from previous studies, suggest that the S1- and S2-mafic and felsic rock types of the LCVs (~95–75 Ma) are the products of two-stage volcanic event that took place during the northward subduction of the northern Neotethys Ocean.</p><p> </p><p>Acknowledgement</p><p>This study was financially supported by Scientific and Technological Research Council of Turkey (TUBITAK) with grant# 112Y365.</p>

Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call