Petrological and geodynamic evolution of the Late Cretaceous subduction-related volcanism in the eastern Sakarya Zone, NE Turkey
Authors: Oğuz Saka Simge , Aydin Faruk , Şen Cüneyt , Dokuz Abdurrahman , Aiglsperger Thomas , Uysal İbrahim , Kandemir Raif , Karsli Orhan , Sarı Bilal , Başer Rasim 
Published: March 2020

&lt;p&gt;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-&amp;#199;atak and S2-&amp;#199;a&amp;#287;layan) and felsic/acidic (S1-K&amp;#305;z&amp;#305;lkaya 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-&amp;#199;a&amp;#287;layan basaltic rocks having crystallised at higher temperatures and under deeper crustal conditions (T = 1128 &amp;#177; 15 &lt;sup&gt;o&lt;/sup&gt;C, P = 6.5 &amp;#177; 0.7 kbar and D = 19.5 &amp;#177; 2.1 km) than those of the S1-&amp;#199;atak rocks (T = 1073 &amp;#177; 11 &lt;sup&gt;o&lt;/sup&gt;C, P = 2.2 &amp;#177; 1.0 kbar, D = 6.6 &amp;#177; 3.0 km).&lt;/p&gt;&lt;p&gt;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 &lt;sup&gt;87&lt;/sup&gt;Sr/&lt;sup&gt;86&lt;/sup&gt;Sr&lt;sub&gt;(i)&lt;/sub&gt; (0.7044&amp;#8211;0.7071) and &amp;#603;Nd&lt;sub&gt;(i)&lt;/sub&gt; values (-0.63 to +3.47) as well as &lt;sup&gt;206&lt;/sup&gt;Pb/&lt;sup&gt;204&lt;/sup&gt;Pb&lt;sub&gt;(i)&lt;/sub&gt; (18.07 to 18.56), &lt;sup&gt;207&lt;/sup&gt;Pb/&lt;sup&gt;204&lt;/sup&gt;Pb&lt;sub&gt;(i)&lt;/sub&gt; (15.57 to 15.62) and &lt;sup&gt;208&lt;/sup&gt;Pb/&lt;sup&gt;204&lt;/sup&gt;Pb&lt;sub&gt;(i)&lt;/sub&gt; (37.12 to 38.55) ratios show very limited variation. The average &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O isotope values of the S1-K&amp;#305;z&amp;#305;lkaya (5.3 &amp;#177; 0.5&amp;#8240;) and S2-Tirebolu (4.9 &amp;#177; 0.8&amp;#8240;) zircons are quite consistent with average mantle values (5.3 &amp;#177; 0.3&amp;#8240;). The similar isotopic compositions of the studied mafic and felsic volcanic rocks, and the relatively high Mg# values (up to 0.4&amp;#8211;0.51) of the felsic samples indicate a cogenetic origin. The parent magmas of the S1-&amp;#199;atak and S2-&amp;#199;a&amp;#287;layan 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-K&amp;#305;z&amp;#305;lkaya (mainly dacitic) and S2-Tirebolu (rhyolitic to trachytic) felsic rocks were particularly controlled by metasomatised mantle&amp;#8211;crust interaction and MASH zone plus shallow crustal fractionation processes.&lt;/p&gt;&lt;p&gt;Our data, together with data from previous studies, suggest that the S1- and S2-mafic and felsic rock types of the LCVs (~95&amp;#8211;75 Ma) are the products of two-stage volcanic event that took place during the northward subduction of the northern Neotethys Ocean.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Acknowledgement&lt;/p&gt;&lt;p&gt;This study was financially supported by Scientific and Technological Research Council of Turkey (TUBITAK) with grant# 112Y365.&lt;/p&gt;