Nature of clays in Late Cretaceous dacitic rocks in the eastern Sakarya Zone (NE Turkey): a geochemical and isotopic approach

Ferkan SİPAHİ; Mehmet Ali GÜCER; Münür Burhan SADIKLAR

doi:10.3906/yer-2002-9

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

10.5194/egusphere-egu2020-21241 ◽

2020 ◽

Author(s):

Simge Oğuz Saka ◽

Faruk Aydin ◽

Cüneyt Şen ◽

Abdurrahman Dokuz ◽

Thomas Aiglsperger ◽

...

Keyword(s):

Late Cretaceous ◽

Volcanic Rocks ◽

Geochemical Data ◽

Spinel Lherzolite ◽

Volcanic Event ◽

Geochemical Composition ◽

Basaltic Rocks ◽

Rock Types ◽

Sakarya Zone ◽

Felsic Volcanic

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

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