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- Aydin, Faruk, et al.
(författare)
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Temporal, geochemical and geodynamic evolution of the Late Cretaceous subduction zone volcanism in the eastern Sakarya Zone, NE Turkey : Implications for mantle-crust interaction in an arc setting
- 2020
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Ingår i: Journal of Asian Earth Sciences. - : Elsevier. - 1367-9120 .- 1878-5786. ; 192
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Tidskriftsartikel (refereegranskat)abstract
- The Late Cretaceous Artvin volcanic rocks (LCAVs) from the eastern Sakarya zone (ESZ) of NE Turkey are composed 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–Early Santonian) and (ii) second stage (S2: Late Santonian–Campanian). Clinopyroxene thermobarometric results point that the S2-Çağlayan basaltic rocks have crystallised at higher temperatures and under deeper crustal conditions than those of the S1-Çatak basaltic rocks.The LCAVs 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) (0.7044–0.7071) and ɛNd(i) values (−0.63 to + 3.47) as well as 206Pb/204Pb(i) (18.07–18.56), 207Pb/204Pb(i) (15.57–15.62) and 208Pb/204Pb(i) (37.12–38.55) ratios show very limited variation. 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 + shallow crustal fractionation processes. Our data, together with data from previous studies, suggest that the S1- and S2-mafic and felsic rocks of the LCAVs (~95–75 Ma) are the products of two-stage volcanic event that took place during the northward subduction of the northern Neotethys Ocean (NNO).
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| 2. |
- Oğuz-Saka, Simge, et al.
(författare)
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Two-stage bimodal volcanism in a Late Cretaceous arc/back-arc setting, NE Turkey: Constraints from volcano-stratigraphy, zircon U–Pb and 40Ar/39Ar geochronology and whole-rock elemental and Sr-Nd-Pb isotope geochemistry
- 2023
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Ingår i: Lithos. - : Elsevier. - 0024-4937 .- 1872-6143. ; 440-441
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Tidskriftsartikel (refereegranskat)abstract
- The eastern Blacksea magmatic arc (EBMA) in the eastern Sakarya Zone (ESZ) provides an excellent opportunity to investigate birth of an extensional intra-arc and back-arc settings in the Late Cretaceous over the Early Cretaceous northern passive margin of the Neotethys Ocean. Volcano-stratigraphy clearly shows that the Late Cretaceous volcanic activity of the EBMA occurred in two major phases. Bimodality, characterized by mafic/basaltic rocks at the base and felsic/silicic types on top of it, is a typical feature of the lower (LVS) and upper (UVS) volcanic successions in the Giresun region of the ESZ. U–Pb and Ar–Ar ages support the volcanic succession as two-stage (LVS: ca. 92–85 and UVS: ca. 83–67 Ma) bimodal volcanism. Both the volcanic successions are represented by similar rock types consisting of tholeiitic to calc-alkaline basalt-basaltic andesites and calc-alkaline to shoshonitic dacite-rhyolites. Basaltic (M1- and M2-series) and felsic/silicic (F1- and F2-series) samples of the LVS and UVS have an arc-like signature with enriched large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs). Also, the felsic/silicic samples of the F1- and F2-series show prominent negative Sr and Eu anomalies (Eu/Eu* = 0.4 to 0.9), suggesting that plagioclase fractionation played a key role on the evolution of both felsic series. Bimodal rock series in two phases have a wide range of 87Sr/86Sr(i) (0.7048–0.7075) and 143Nd/144Nd(i) (0.5123–0.5127) ratios with variable ɛNd(i) values of −3.8 to +3.0. 206Pb/204Pb(i), 207Pb/204Pb(i) and 208Pb/204Pb(i) isotope ratios of the Giresun volcanic rocks vary in the range of 17.97–18.52, 15.55–15.65 and 37.53–38.56, respectively.Geochemical and isotopic data suggest that the parental magma of the M1-basaltic rocks were probably derived from a shallow (spinel-bearing) mantle metasomatized by slab/sediment-derived fluids. In contrast, the M2-basalts seem to have been originated from a deeper mantle source (spinel-garnet transition zone) enriched by slab/sediment-derived fluids and hydrous melts (bulk sediment) metasomatism with some contributions of lower/upper crustal materials. The least evolved basaltic samples in two phases are consistent with moderate (∼10–15%) to high degree (∼20–30%) partial melting of the metasomatized mantle. The silicic melts of the F1- and F2-rocks series, on the other hand, were likely derived from melting of lower crustal materials consisting of meta-basalts/andesites and lesser amount of meta-sediments. Subsequently, these melts experienced FC ± AFC and mixing processes during their ascent and emplacement to generate high-silica (rhyolitic) melts. Our data, combined with previous studies, suggest that two-stage bimodal volcanic rocks of the Late Cretaceous in the ESZ were formed in the transition from an extensional continental intra-arc to a back-arc setting during the northward subduction of the northern branch of Neotethys Ocean.
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