Sayit, Kaan; Çevik, Özlem; Aktağ, Alican; Erdoğu, Burçin; Bamyacı, Onur; Vuruşkan, Osman; Sivil, Coşkun

The jades from Ulucak Höyük (İzmir, Turkey) are green-colored in hand specimen, and combined petrographic, XRD, and whole-rock analyses indicate that they mainly comprise jadeitic clinopyroxene, characterizing them as jadeite-bearing jades. Primitive mantle (PM)-normalized multi-element patterns reveal two distinct chemical groups. Both groups display depletion in Th and U; however, Group 1 shows a narrower elemental range and marked positive Pb anomaly. The second group, on the other hand, displays a wide elemental range in most elements and strong negative anomalies in Zr and Hf ([Nd/Zr]PM = 1.6–4.2; [Sm/Hf]PM = 1.8–3.5). Regarding REE systematics, both groups are characterized by weak positive slopes ([La/Yb]Ch = 1.7–5.3). However, whereas Group 1 shows coherent LREE-enriched trends, Group 2 displays flat- to LREE-enriched patterns with a wide range in Eu. When the geochemical features of Ulucak jades are compared with the high-pressure (HP) metamorphic rocks from Turkey and Greece, the similar multi-element patterns of Syros eclogites (Greece) to Group 2 Ulucak jades make Syros a possible source area for the Ulucak artefacts. On the other hand, the geochemical resemblance of the Sifnos jadeite-bearing gneisses to Group 1 Ulucak jades may raise the possibility of this island being another source for the Ulucak jades.

İncele

Aktağ, Alican; Sayit, Kaan; Furman, Tanya; Peters, Bradley J.

The Sr-Nd-Hf-Pb isotope geochemistry of the Late Miocene Tunceli Volcanics suggests that they are the products of mixed asthenospheric and lithospheric mantle melts. The combined elemental and mineral chemistry data additionally indicate that a pyroxenite component of lithospheric origin is involved in their genesis. Calculations favor melting depths of ∼2 GPa for the Tunceli lavas, that is, deeper than the current lithosphere-asthenosphere boundary beneath Eastern Anatolia. Geochemical data suggest that during regional Neo-Tethyan subduction, dense (i.e., pyroxenite-bearing) domains formed by progressive melt intrusion into the lower lithosphere resulted in gravitational instabilities. This unstable density configuration eventually led to the foundering of the eastern Anatolian lithosphere in the Late Miocene, resulting in progressive melting of fusible pyroxenite-bearing domains at asthenospheric depths. We demonstrate that these pyroxenitic melts mixed with ambient asthenospheric melts and generated the Tunceli lavas.

AtıfScopus7·OpenAlex9

İncele

Aktağ, Alican; Sayit, Kaan; Peters, Bradley J.; Furman, Tanya; Rickli, Jörg

Quaternary Elazığ mafic alkaline volcanism is part of the anorogenic volcanic system of the circum-Mediterranean region, and it provides crucial insights into the chemical nature of the mantle source domains beneath eastern Turkey. Elemental and isotope geochemistry reveals that these mafic lithologies are mainly free of crustal contamination, reflecting geochemical signatures inherited from partial melting of their mantle sources. The trace element and Sr-Nd-Hf-Pb isotope systematics of the most primitive members of this volcanism are consistent with a predominant contribution from a sub-lithospheric component which compositionally resembles component C, believed to be common to global OIBs and MORBs. However, the total range of the isotope data also requires the involvement of two additional mantle components into their genesis: a depleted asthenospheric component (DM) and an enriched component (EM-type) representing metasomatized lithospheric mantle. We propose that the recycled oceanic lithologies with C-like signatures are dispersed in the asthenospheric mantle beneath eastern Anatolia and have undergone mixing with the depleted mantle matrix. When considering these with the melting models, it appears that the garnet-facies partial melts of the C-DM mixture have experienced a small degree of interaction with the melts from an SCLM domain modified by slab-derived melts and/or fluids. The metasomatized SCLM domain may be intrinsic to the eastern Anatolian lithosphere or occur as pods embedded in the asthenosphere. The chemical characteristics of the Elazığ Volcanics may confirm the wide-range dispersal of the common component in the sub-lithospheric mantle beneath the region extending from western Europe to eastern Turkey. However, the common component resides beneath Anatolia appear to have distinct composition (i.e., Pb isotope systematics) than the ubiquitous component shared mostly by European intraplate volcanics (i.e., LVC/EAR).

AtıfScopus3·OpenAlex4

İncele

Aktağ, Alican; Önal, Ayten Öztüfekçi; Sayit, Kaan

The East Anatolian Accretionary Complex (EAAC) comprises an ideal example of post-collisional volcanism within the Africa-Eurasia collision zone. The Miocene mafic Tunceli Volcanics, as a part of this post-collisional volcanic system, are located in the western termination of EAAC. The mafic Tunceli Volcanics are characterized by mildly alkaline and tholeiitic basalts, in which olivine, clinopyroxene and plagioclase characterize the main mineralogy. The role of fractional crystallization (FC) and assimilation combined with fractional crystallization (AFC) processes appear to be negligible in the petrogenesis of the primitive mafic Tunceli Volcanics. Relative enrichment in large ion lithophile elements (LILE), Th and La over high field strength elements (HFSE) and heavy rare earth elements (HREE) suggest contribution from a metasomatized mantle source. The wide range of ratios displayed by these elements also calls for some asthenospheric input for the genesis of these volcanics. The metasomatizing agents can be attributed to a past subduction event, probably during the closure of Neotethys. Considering also the geophysical constraints, which limits the lithospheric thickness to about 70–75 km around the region, a melt mixing between lithospheric and asthenospheric melts generated at different depths appear to be an important process in the petrogenesis of these lavas. The combined geochemical and geophysical data, therefore, necessitate a geodynamic model with some remnant lithospheric mantle underlying the Eastern Anatolian region.

AtıfScopus10·WoS11·OpenAlex13

İncele

Çimen, Okay; Göncüoğlu, M. Cemal; Simonetti, Antonio; Sayit, Kaan

The Central Pontides in northern Anatolia is located on the accretionary complex formed by the closure of Neotethyan Intra-Pontide Ocean between the southern Eurasian margin (Istanbul-Zonguldak Terrane) and the Cimmerian Sakarya Composite Terrane. Among other components of the oceanic lithosphere, it comprises not yet well-dated felsic igneous rocks formed in arc-basin as well as continent margin settings. In-situ U-Pb age results for zircons from the arc-basin system (öangaldağ Metamorphic Complex) and the continental arc (Devrekani Metadiorite and Granitoid) yield ages of 176 ± 6 Ma, 163 ± 9 Ma and 165 ± 3 Ma, respectively. Corresponding in-situ average (initial) 176Hf/177Hf initial ratios are 0.28261 ± 0.00003, 0.28267 ± 0.00002 and 0.28290 ± 0.00004 for these units and indicative of a subduction-modified mantle source. The new U-Pb ages and Hf isotope data from these oceanic and continental arc units together with regional geological constraints support the presence of a multiple subduction system within the Intra-Pontide Ocean during the Middle Jurassic.

AtıfScopus39·OpenAlex32

İncele

Çimen, Okay; Göncüoğlu, M. Cemal; Simonetti, Antonio; Sayit, Kaan

The Central Pontides (Turkey) includes several igneous complexes, which are predominantly Permo-Carboniferous and Middle Jurassic in age. The Çangaldağ Pluton is one of the largest igneous bodies located in the northern Central Pontides, whose age and tectono-magmatic evaluation is important to constrain the geological evolution of the Northern Neotethys. The pluton tectonically overlies the Çangaldağ Metamorphic Complex, which represents an arc–back-arc complex of Middle Jurassic age. The Çangaldağ Pluton consists mainly of non-metamorphic gabbroic diorite, dacite porphyry, and lesser amount of granitic rocks. Geochemically, the various rock types are akin to volcanic arc magmas displaying Th/Nb and light rare earth element/heavy rare earth element enrichments. In-situ U–Pb age results of zircons from dacite porphyry and granite samples yield ages of 161 ± 5 Ma and 170 ± 2 Ma, respectively. Corresponding in-situ average 176Hf/177Hf initial ratios are 0.28287 ± 0.00004 and 0.28213 ± 0.00002 for the dacite porphyry and granite samples, respectively. These results are consistent with derivation from a subduction-modified mantle source. Based on Hf isotope compositions, TDM model ages vary between 624 and 1512 Ma and suggest that the arc magmatism associated with the Çangaldağ Pluton may have involved partial melting of Neoproterozoic/Mesoproterozoic crustal rocks, a common feature in Gondwana-derived terranes. The geochemical, Hf isotope, and geochronological data reported here confirm the presence of a continental arc system during the Middle Jurassic in the Central Pontides, and suggests that the Çangaldağ Pluton formed during northward subduction of the Intra-Pontide branch of the Northern Neotethys.

AtıfScopus35·OpenAlex32

İncele

Çimen, Okay; Göncüoğlu, M. Cemal; Sayit, Kaan

The Cangaldağ Complex in northern central Turkey is one of the main tectonic units of the Central Pontide Structural Complex that represents the remains of the poorly known Intra-Pontide branch of the Neotethys. It comprises low-grade metamorphic rocks of intrusive, extrusive, and volcaniclastic origin displaying a wide range of felsic to mafic compositions. Petrographically the complex consists of basalts-andesites-rhyodacites and tuffs with minor amount of gabbros and diabases. On the basis of geochemistry, the Cangaldağ samples are of subalkaline character and represented by both primitive and evolved members. All rock types are variably depleted in Nb compared to LREEs, similar to the lavas from subduction-related tectonic settings. In N-MORB normalized plots, the primitive members are separated into 3 groups on the basis of levels of enrichment. The first group is highly depleted and displays characteristics of boninitic lavas. The second group is relatively enriched compared to the first group but still more depleted than N-MORB. The third group, however, is the most enriched one among the three, whose level of enrichment is around that of N-MORB. The overall geochemical features suggest that the Cangaldağ Complex has been generated with the involvement of a subductionmodified mantle source. The chemistry of the primitive members further indicates that the melts generated for the formation of the Cangaldağ Complex probably occurred in both arc and back-arc regions above an intraoceanic subduction within the Intra-Pontide branch of the Neotethys.

AtıfScopus39·WoS39·OpenAlex31

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