| 1. |
- Karsli, O., et al.
(författare)
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Ordovician S-type granites in the western Sakarya Zone, NW Turkey; linkage to a back-arc setting
- 2023
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937. ; 442-443
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Tidskriftsartikel (refereegranskat)abstract
- Turkey's Early Paleozoic tectonic evolution has received much attention in recent years. Early Paleozoic intrusive rocks are mainly distributed across Europe, Turkey (Istanbul-Zonguldak Zone, Strandja Zone, and Tauride Block), and Iran. However, the Early Paleozoic rocks have not yet been identified in north Turkey's Sakarya Zone, and thus the Early Paleozoic paleogeography of the Sakarya Zone remains enigmatic. Here, we provide new field observations, petrography, geochemistry, and geochronology of the western Sakarya Zone to identify the nature, origin, and tectonic setting of the Ordovician magmatic rocks cropping out in the So center dot gut area (Bilecik, northwest Turkey). Our Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb analyses on zircons suggest that the So center dot gut metagranites were emplaced at-484-461 Ma (except two zircons with ages of 490 and 494 Ma). There are abundant inherited zircon cores in the So center dot gut metagranites, with ages of >500 Ma to-2.2 Ga. The inherited Cadomian cores give concordant ages of 588 and 572 Ma. The So center dot gut metagranites are felsic and have high SiO2 (72-76 wt%) and K2O (4.1-5.3 wt%) contents, with high K2O/Na2O ratios (1.2-1.9), and low Mg# (17-35) values. The samples are Ca-poor (CaO = 0.52-0.68 wt%) and show peraluminous [A/CNK = molar Al2O3/(K2O + CaO + Na2O) = 1.15-1.28] and high-K calc-alkaline geochemical characters, with high modal content of muscovite (-10%), consistent with S-type compositions. The samples have low REE concentrations, with negative Eu anomalies. Ordovician zircon rims show epsilon Hf(t) values of +3.6 to-35.4, whereas inherited zircon cores have epsilon Hf(t) values of +33.9 to-26.1. Our data, in conjunction with previous studies, suggest that the So center dot gut metagranites were generated by fluid-absent muscovite-dehydration melting of metasediments accumulated in a back-arc setting. This back-arc basin was characterized by a denuded continental crust with abundant pelite-dominated sediments and minor input of juvenile mafic melts. Our results, combined with previously published data and paleogeographic reconstructions, allow us to conclude that the Ordovician S-type granites were formed by progressive back-arc extension and crustal thinning prompted by the rollback of the southward subducting oceanic-lithosphere slab. This led to the opening of the Rheic Ocean on the northern side of Gondwana in response to the final closure and termination of the Tornquist Ocean as a branch of the Iapetus Ocean. We argue that the Ordovician S-type granites from the northern side of Gondwana could signal significant crustal reworking away from any clear continental collision zone.
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| 2. |
- Karsli, O., et al.
(författare)
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Silurian to Early Devonian arc magmatism in the western Sakarya Zone (NW Turkey), with inference to the closure of the Rheic Ocean
- 2020
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937. ; 370-371:October
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Tidskriftsartikel (refereegranskat)abstract
- The Rheic Ocean is the most significant Paleozoic ocean that detached peri-Gondwana terranes from the northern Gondwana margin throughout the closure of the Iapetus Ocean. The suture of the Rheic Ocean spreads from Mexico to the Middle East, and the timing of its final closure is well-documented by the rocks formed in the Variscan-Alleghanian-Ouachita orogeny which led to the formation of the supercontinent Pangaea. However, as robust paleomagnetic and quantitative data are mostly lacking, the onset and evolution of the subduction of the Rheic Ocean are highly speculative, and they require further confirmation. Recently, the well-preserved metagranitoids along the western Sakarya Zone (SZ) in Anatolia have been identified, and they provide new data that improve our knowledge on the evolution of the Early Paleozoic Rheic Ocean along the northern Gondwana. Here, we present new geochronological, in situ zircon Hf isotope, and whole-rock geochemical analyses of these metagranitoids from the western SZ to enhance our understanding of the subduction processes of the Rheic Ocean. IA-ICP-MS zircon U-Pb dating demonstrated that the Boziiyuk and Borcak metagranitoids from the western SZ were emplaced during the Silurian to Early Devonian (431 +/- 2.7 to 403 +/- 3.5 Ma). The both granitoids have medium- to high-K. calc-alkaline magmatic character, and exhibit peraluminous to slightly metaluminous geochemical signature. They show a typical arc pattern in terms of trace elements and have a uniform, moderate negative epsilon(Hf) (t) of -3.2 to -9.7, with Mesoproterozoic Hf depleted mantle model ages (T-DM1 = 12 to 1.4 Ga). The geochemical and isotopic characteristics are not consistent with those of depleted mantle melts and melts derived from the crustal rocks in an intracontinental environment. Instead, the parental magma is likely generated from the partial melting of a homogeneous and enriched mantle wedge source. We propose that the Silurian to Early Devonian arc-related magmatism is associated with a northward subduction episode of the Rheic Oceanic lithosphere beneath the peri-Gondwana terranes. Hence, we consider that the opening of Paleotethys Ocean formed in a back-arc basin of subduction in Andean style to the north rather than a continental rift to the south in response to south-directed and short-lived supra-subduction zone (SSZ)-type subduction during the Silurian to Early Devonian. (C) 2020 Elsevier B.V. All rights reserved.
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| 3. |
- Karsli, O., et al.
(författare)
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Tracking the timing of Neotethyan oceanic slab break-off: Geochronology and geochemistry of the quartz diorite porphyries, NE Turkey
- 2020
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Ingår i: Journal of Asian Earth Sciences. - : Elsevier BV. - 1367-9120. ; 200
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Tidskriftsartikel (refereegranskat)abstract
- The initiation of the break-off of the northern branch of the Neotethyan oceanic lithosphere is an important but poorly understood event in the geology of the Sakarya Zone (SZ) in northeastern Turkey. Although it is wellknown that Latest Cretaceous intrusives (-70 Ma) and early Eocene adakitic magmatic rocks are present in the eastern SZ, the outcrops of the early Eocene non-adakitic rocks are very limited, and their tectono-magmatic evolution has not been studied. We describe a small outcrop of non-adakitic quartz diorite porphyry in the Kov area of the Gumushane region in northeastern Turkey. The genesis of these porphyries is significant in evaluating the syn-to post-collision-related magmatism. The LA-ICP-MS zircon U-Pb dating revealed that the Kov quartz diorite porphyries (KQDP) formed at ca. 50 Ma, coeval with adakitic rocks, and-20 Myr later than the slab rollback-related intrusive rocks. The KQDPs are calc-alkaline in composition and enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), with significant negative anomalies of Nb, Ta, and Ti but positive anomalies of Th, U, and Pb. Isotopic compositions of the samples show limited range of variation and slight enrichment of 87Sr/86Sr(t) (0.70489 to 0.70555), epsilon Nd(t) (-1.4 to -1.2) with TDM of 1.11 to 1.61 Ga. Pb isotopic ratios of the samples point to an enriched mantle source. They were likely crystallized from the melt that originated from an EM2-type spinel-facies subcontinental lithospheric mantle (SCLM), followed by the fractionation with insignificant crustal assimilation. The SCLM was metasomatically enriched, and the metasomatic agent was likely H2O-rich fluids rather than sediments released from subducting oceanic crust during the Late Cretaceous closure of the Neotethyan oceanic lithosphere. In conjunction with the geological background and previous data, we propose that the generation of the KQDPs resulted from a slab break-off event that caused ascending or infiltration of hot asthenosphere, triggering mantle melting. Such sporadic occurrences of the KQDPs, with coeval adakitic rocks in the SZ, are likely associated with the onset of extensional tectonics due to the earlier stage of slab break-off along the region during the early Eocene period.
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| 4. |
- 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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