Estimation of Natural Radionuclides’ Concentration of the Plutonic Rocks in the Sakarya Zone, Turkey Using Multivariate Statistical Methods

The study aimed to determine the natural radioactivity levels of 226Ra, 232Th, and 40K by the Gamma-Ray spectrometry method, and radiological hazard parameters of the plutonic rocks in the Western and Central Sakarya Zone and to analyze the data using multivariate statistical methods. The average radiological values of samples were determined as 40K (1295.3 Bq kg−1) > 232Th (132.1 Bq kg−1) > 226Ra (119.7 Bq kg−1). According to the skewness values of the distributions of the examined radionuclides, 226Ra (2.1) and 232Th (0.7) seemed to be positively right-skewed while 40K (−0.2) had a negatively right-skewed histogram. On the other hand, the following kurtosis values were calculated for the distributions: 226Ra (5.8 > 3), 232Th (−0.7), and 40K (−0.8). Kolmogorov–Smirnov and Shapiro–Wilk tests were applied to the data to test their normality. Therefore, Spearman’s correlation coefficient method was performed. The radionuclides of 226Ra and 232Th were found to have a positive correlation with radiological hazard parameters of the samples. 2 (two)-related factors identified, and the cumulative value was calculated to be 98.7% on the basis of the Scree Plot. According to the hierarchical cluster analysis, the samples that are grouped with those from Camlik region are prominent. The average radioactivity values of Camlik, Sogukpinar, Karacabey, and Sogut (except for 232Th) regions were detected to be higher than the world averages while the value of 40K was also found to be higher than the average values of various countries in the world.

Petrological and geodynamic evolution of the Late Cretaceous subduction-related volcanism in the eastern Sakarya Zone, NE Turkey

<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>

Petrogenesis and geodynamic significance of the early Eocene quartz diorite porphyries from the eastern Sakarya Zone, NE Turkey

<p>Although the presence of Latest Cretaceous intrusives (~70 Ma) and the early Eocene adakitic magmatic rocks (~57-50 Ma) in the eastern Sakarya Zone are well-known, the early Eocene non-adakitic rocks are very limited and have not been studied in terms of tectono-magmatic evolution. We described a small outcrop of non-adakitic quartz diorite porphyry in Kov area of the Gümüşhane from NE Turkey of which the genesis is significant in evaluating the syn- to post-collision-related magmatism. The LA-ICP-MS zircon U-Pb dating reveal that the Kov quartz diorite porphyries formed at ca. 50 Ma, coeval with adakitic rocks, ~20 Ma later than the slab roll-back-related intrusive rocks. The Kov porphyries are calc-alkaline in composition and enriched in large ion lithophile elements (LILEs), light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), with significant negative anomalies at Nb, Ta, and Ti but positive anomalies at Th, U, and Pb. Isotopic compositions of the samples show limited range of variation and slight enrichment of <sup>87</sup>Sr/<sup>86</sup>Sr<sub>(i)</sub> (0.70489 to 0.70555), e<sub>Nd(i)</sub> (-1.4 to -1.2) with T<sub>DM</sub>  of 1.11 to 1.61 Ga. Pb isotopic ratios of the samples point to an enriched mantle source. They probably were crystallized from the melt that originated by low-degree partial melting (~1-2%) of an EMII-type spinel-facies subcontinental lithospheric mantle (SCLM), followed by the fractionation of clinopyroxene with insignificant crustal assimilation. The SCLM was metasomatically enriched and the metasomatic agent was likely H<sub>2</sub>O-rich fluids rather than sediments released from subducting oceanic crust during the Late Cretaceous closure of the Neotethyan oceanic lithosphere.</p><p>In conjunction with the geological background and previous data, we envisage that generation of the Kov porphyries is resulted from a slab break-off event that caused ascending or infiltration of hot asthenosphere triggering mantle melting. Such sporadic occurrences of the porphyries, with coeval adakitic rocks in the Sakarya Zone are likely associated with the onset of extensional tectonics due to the earlier stage of slab break-off along the region during early Eocene period.</p><p> </p><p>Acknowledgement</p><p>This work was financially supported by Scientific and Technological Research Council of Turkey (TUBITAK) with grant #108Y200.</p>

New constraints from U–Pb dating of detrital zircons on the palaeogeographic origin of metasediments in the Talea Ori, central Crete

High-pressure low-temperature metamorphic sediments of the Phyllite–Quartzite unit sensu stricto and the Talea Ori group are investigated in the field, microstructurally and by U–Pb dating of detrital zircons to shed light on their palaeogeographic origin. Zircon age spectra with ages >450 Ma of the Phyllite–Quartzite unit sensu stricto indicate a palaeogeographic origin at the northern margin of East Gondwana. In contrast, the lower stratigraphic, siliciclastic formations of the Talea Ori group show a high number of well-rounded Cambrian to Early Carboniferous aged zircons and a Neoproterozoic zircon age spectrum with East Gondwana affinity. Based on the comparison of zircon age data, a possible distal sediment source is the Sakarya Zone at the southern active margin of Eurasia. To reconcile the zircon data with the geological observations we propose different alternative models, or a combination of these, including sediment transport from the Sakarya Zone and/or a westerly source towards the northern margin of Gondwana as well as terrane-displacement of the Sakarya Zone. Also, a palaeogeographic origin of the Talea Ori group at the southern active margin of Eurasia cannot be excluded. This alternative, however, would not be consistent with the usually assumed association of the Talea Ori group with the Plattenkalk unit characterized by a palaeogeographic origin at the northern margin of Gondwana.