Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleYalnız künye2012A-type granitoids from the Eastern Pontides, NE Turkey: Records for generation of hybrid A-type rocks in a subduction-related environment
Karsli, Orhan; Caran, Şemsettin; Dokuz, Abdurrahman; Çoban, Hakan; Chen, Bin; Kandemir, Raif
The Eastern Pontides is characterized by the many of intrusive bodies formed throughout the late Mesozoic-early Cenozoic. Most of these are I-type granitoids, but here, we present for the first time an A-type pluton from the region to assess source characteristics and geodynamic implications. The A-type Pirnalli pluton has a SHRIMP zircon U-Pb age of 81.2±1Ma. It is composed of granite, syenite and quartz monzonite, and its enclaves are monzonitic in composition with elevated Ga/Al ratios and low Mg# (<42). The pluton is dominantly metaluminous (A/CNK=0.88 to 1.00) and belong to shoshonitic and ultra-potassic series. The samples are highly enriched in LREE and show significant negative Eu (Eu/Eu *=0.33 to 0.92), Ba, Nb, Sr and Ti anomalies in the spidergrams. The host rocks and their enclaves posses quite similar Sr-Nd isotopic compositions (I Sr=0.70693 to 0.70736, ε Nd (81Ma)=-2.6 to -2.0, T DM=0.94 to 1.12Ga), pointing to a lower crustal parental magma with a minor contribution of lithospheric mantle. We hypothesize that upwelling of asthenosphere triggered melting of chemically enriched upper mantle and basic magma formed. Melting of lower crust was provided by the underplating of this basic magma. Mixing between lower crust- and mantle-derived melts at depths of lower crust appears to be most reasonable petrogenetic process responsible for generation of the pluton. Sr-Nd isotope modeling suggests mixing of 82-90% of the lower crustal-derived melt with ~10-18% of the mantle-derived melt. Then the hybrid melt ascended to shallower crustal level and underwent a limited fractionation process to generate a variety of rock types. Our data also suggest that the A-type Pirnalli pluton likely formed at an extensional environment of active continental margin throughout the late Cretaceous. Ongoing extension then led to opening of Black Sea as a back-arc basin further north of the Eastern Pontides.
- Proje2011Triyas volkanitlerinin petrolojik özellikleri, Gümüşhane: Doğu Pontidlerin geç Paleozoyik - erken Mesozoyik jeodinamik evrimi için bulgular
Dokuz, İbrahim; Uysal, İbrahim; Karsli, Orhan; Kandemir, Raif
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- Proje2011Kalk-alkalen lamprofirlerin petrojenezleri, KD Türkiye: Doğu pontidlerin senozoyik jeodinamik evrimi için yeni bulgular
Uysal, İbrahim; Dokuz, Abdurrahman; Karsli, Orhan; Aydın, Faruk; Kandemir, Raif
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- MakaleAçık Erişim2011First Report of a Trilobite in the Carboniferous of Eastern Pontides, NE Turkey
Kandemir, Raif; Lerosey-Aubril, Rudy
The pre-Mesozoic basement of the Eastern Pontides consists of a Permo-Carboniferous sedimentary sequence including the Catalcesme and Hardisi formations. The Catalcesme Formation has yielded rich assemblages of fusulinids, corals, gastropods, brachiopods, bryozoans, algae, conodonts and plants. Hitherto trilobites were unknown from this formation; here we report the discovery of a pygidium from a dark grey limestone bed near the top. Trilobites are a minor component of benthic marine communities during the Late Pennsylvanian, and to our knowledge, the discovery of this pygidium constitutes the first report of their occurrence in deposits of this age in Turkey. The morphological characteristics of the specimen, especially the number of axial rings and pleural ribs and the well-defined border (Owens 1983), suggest that it probably belongs to an undescribed species of Ditomopyge Newell, 1931 (Ditomopyginae). It also exhibits a distortion of the posterior part of the axis, and a shortening (right side) or a fusion (left side) of some pleural ribs, which is tentatively interpreted as repaired injuries or the results of a developmental dysfunction.
- MakaleYalnız künye2011A new Early Jurassic brachiopod fauna from the Eastern Pontides (Turkey)
Vörös, Attila; Kandemir, Raif
A newly collected Early Jurassic brachiopod fauna from the Kocamantaşi section (Gümüşhane region, Eastern Pontides, Turkey) yielded 160 specimens and 13 species (4 rhynchonellids, 3 spirifennids, 6 terebratulids). Apart from some long-ranging forms, five species prove the Late Pliensbachian age of the fauna. The paleoenvironmental setting of the Kocamantaşi fauna shows analogies to the Alpine Hierlatz limestones. On the basis of common lithological characters, bedding features and sedimentary associations, this lithofacies is interpreted as a complex of submarine, biodetrital talus associated with fault-related submarine rocky slopes. The numerical comparison of the Kocamantaşi brachiopod fauna to Pliensbachian brachiopod faunas of Europe revealed that the faunal similarity was the highest to Kotel (Balkans) and the Crimea. Very strong affinity was recorded to further NW-European faunas, whereas very low, or no similarity was recognized to the Mediterranean faunas. This paleobiogeographical result supports the hypothesis that in the Late Pliensbachian the Eastern Pontide segment of the Cimmerian microcontinent was far from the Gondwana and close to the Eurasian margin of the Tethys.
- MakaleAçık Erişim2011Early abyssal- and late SSZ-type vestiges of the Rheic oceanic mantle in the Variscan basement of the Sakarya Zone, NE Turkey: Implications for the sense of subduction and opening of the Paleotethys
Dokuz, Abdurrahman; Uysal, Ibrahim; Kaliwoda, Melanie; Karsli, Orhan; Ottley, Chris J.; Kandemir, Raif
The boundary between the Gondwana and Laurussia, or a terrane separated from it, is traced by a suture recording the closure of the Rheic ocean in the Pulur, Beyçam and Kurtoǧlu areas of the eastern Sakarya Zone of Turkey. Pulur lherzolite has a lower Cr# [100Cr/(Cr+Al)=5-37] of the spinel and slightly enriched flat medium-heavy rare earth element (M-HREE) whole-rock pattern typical for those of the fertile abyssal-type lherzolite. By contrast, the Beyçam harzburgite displays the mineralogical and geochemical features of a moderately depleted residue at a supra subduction zone (SSZ). Some of spinels from the Beyçam peridotites show TiO2 contents (0.15-0.48wt.%) identical to a later interaction with a melt of island-arc tholeiite (IAT) composition. Meta-basalt from the Beyçam area is the representative of such a melt and displays the whole-rock M-HREE pattern of a complementary product of the Beyçam harzburgite. Data presented in this study support the primarily northward directed closure of the Rheic ocean, but suggest that the Variscan basement in the eastern part of the Sakarya Zone consists of mantle peridotites formed in a south-vergent SSZ. This dual polarity of subduction in the Rheic ocean, at least in the second half of its closure, is also favored by the geological structure and lithological diversity of the Variscan rocks. These are: (1) spatial distribution of the peridotites, e.g., SSZ-type harzburgites to the north and abyssal-type lherzolites to the south, (2) lack of high-pressure metamorphic rocks, (3) decrease in the degree of Variscan metamorphism toward the north, and (4) emplacement of Variscan syn-collisional magmatism into the low grade metamorphic rocks to the north. Paleotethys was the other ocean of the region created in the Late Paleozoic. Northward subduction of the Rheic ocean from Early Devonian to Early Carboniferous appears to be the most plausible mechanism responsible for the opening of Paleotethys. In this scenario the Paleotethys is envisaged as a back-arc basin opened to the north in the wake of separated terranes from Laurussia. Onset of trench-Rheic mid-ocean ridge collision in the Early Devonian along the northern margin of Laurussia has been proposed to account for the initiation of SSZ-type subduction to the south. The short duration of this subduction appears insufficient to open a fully developed back-arc basin to the south because the elimination of Rheic mid-ocean ridge to the north accelerated the oceanic closure.
- MakaleYalnız künye2011The Sumela Monastery slope in Maçka, Trabzon, Northeast Turkey: Rock mass properties and stability assessment
Gelişli, Kenan; Şeren, Aysel; Babacan, Ali Erden; Çataklı, Aycan; Ersoy, Hakan; Kandemir, Raif
In 2001, rock falls occurred on the southern slope of the Sumela Monastery, which was built on a cliff in Trabzon, north east Turkey, and is visited by many tourists. Considering the steepness of the slope and difficulty of access, rock classifications were made based on seismic wave velocity, rock mass quality (Q), rock quality designation (RQD) and rock mass rating (RMR). The results indicated extremely poor to very poor rock in the cracked, fractured and weathered parts and poor to fair rock in the intact parts of the monastery slope. As a consequence, rock fall, slide and rolling may occur from time to time. These constitute a hazard to the facilities of the monastery and access paths. It is recommended that cracked areas are strengthened with cement-based materials, that accumulated rocks are removed, and that retaining walls are constructed on solid rock around the unstable rock blocks.
- MakaleYalnız künye2011Adakite-like granitoid porphyries in the Eastern Pontides, NE Turkey: Potential parental melts and geodynamic implications
Karsli, Orhan; Ketenci, Murat; Uysal, Ibrahim; Dokuz, Abdurrahman; Aydin, Faruk; Chen, Bin; Kandemir, Raif; Wijbrans, Jan
The tectonic setting of the Eastern Pontides during the late Mesozoic to early Cenozoic remains a subject of debate. Petrogenesis of adakite-like granitoid porphyries plays a critical role in determining the nature of the lower continental crust and mantle dynamics during orogenic processes in the region. Here we describe, for the first time, the late Paleocene to early Eocene adakite-like granitoid porphyries from the northern part of the Eastern Pontides although their counterparts in the southern part have recently been found. The adakitic porphyries, which emplaced into the subduction-related Turonian-Santonian volcanics from northern part of the region, consist of I-type calc-alkaline quartz monzonite-tonalite (SiO2 = 62.89-65.07 wt.%) and high-k calc-alkaline granodiorite-granite associations (SiO2 = 69.06-70.43 wt.%). The former displays peraluminous to metaluminous signatures, whereas the latter shows peraluminous geochemical character. The granite-granodiorite porphyries have high K2O (3.32-3.84 wt.%), and low Na2O (3.48-4.61 wt.%) and MgO (0.91-1.04 wt.%) relative to the quartz monzonite-tonalite association (K2O = 1.50-1.92 wt.%; Na2O = 4.08-6.45 wt.%; MgO = 1.44-2.07 wt.%). Ar-Ar geochronology studies on the amphibole separates reveal that the adakite-like porphyries have a crystallization ages of 51.34 +/- 0.27 to 53.55 +/- 0.34 Ma. Here, we contend that these rocks were formed by partial fusion of a mafic lower continental crust in a collisional phase but not in a subduction setting. All the samples exhibit the typical geochemical characteristics of adakite, that is, high Sr (250-1141 ppm), high Sr/Y ratios (16-147), low Y (6.8-14.8 ppm) and low HREE concentrations; they are similar to adakites formed by slab melting associated with the subduction zone. However, the rocks exhibit heterogeneity in isotopic composition, with I-Sr ranging from 0.70554 to 0.70986, epsilon(Nd) (51 Ma) from -8.5 to -0.9 and Nd model ages from 0.72 to 1.26 Ga. The samples are characterized by relatively high Th, Th/U and no significant Eu anomalies, implying that garnet was stable in their source during partial melting. The compositional diversity between rock groups is probably related to partial melting of heterogeneous lower crustal source. All of the features are inconsistent with a slab-melting origin and slab-related petrogenetic model, but instead, they favor an origin by melting of heterogeneous lower continental crust due to a thermal anomaly that was induced by the upwelling of the asthenosphere through a slab break-off in a collisional setting. These interpretations argue against the evidence for the presence of an early Cenozoic arc setting in the Eastern Pontides. Instead, the early Cenozoic time in the region may be attributed to a geodynamic response to a post-collisional uplift phase that occurred along the continent-continent collision between the Pontide and the Anatolide-Tauride blocks. (C) 2011 Elsevier B.V. All rights reserved.
- Proje2010Adakit benzeri porfirlerin petrolojik özellikleri, KD Türkiye: Doğu pontidler'in üst kretase sonrası jeodinamik modeli için yeni bulgular
Wijbrans, Jan; Uysal, İbrahim; Chen, Bın; Karsli, Orhan; Erduran, Murat; Boztuğ, Durmuş; Kandemir, Raif
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- MakaleYalnız künye2010Generation of the Early Cenozoic adakitic volcanism by partial melting of mafic lower crust, Eastern Turkey: Implications for crustal thickening to delamination
Karsli, Orhan; Dokuz, Abdurrahman; Uysal, Ibrahim; Aydin, Faruk; Kandemir, Raif; Wijbrans, Jan
Early Cenozoic (48-50 Ma) adakitic volcanic rocks from the Eastern Pontides, NE Turkey, consist of calc-alkaline and high-K calc-alkaline andesite and dacite, with SiO2 contents ranging from 56.01 to 65.44 wt.%. This is the first time that Early Eocene volcanism and adakites have been reported from the region. The rocks are composed of plagioclase, amphibole, quartz, and Mg-rich biotite. They have high and low-Mg# values ranging from 55 to 62 and 13 to 42, respectively. High-Mg# rocks have higher Ni and Co contents than low-Mg# samples. The rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements, depletions in Nb, Ta and Ti and have high La/Yb and Sr/Y ratios. Their relative high ISr (0.70474-0.70640) and low εNd (50 Ma) values (- 2.3 to 0.8) are inconsistent with an origin as partial melts of a subducted oceanic slab. Combined major- and trace element and Sr-Nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region, where a transition from a collision to an extension stage has created thickening and delamination of the Pontide mafic lower crust at 50 Ma. The high-Mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle, and its subsequent interaction with the mantle peridotite during upward transport, leaving garnet as the residual phase, elevates the MgO content and Mg# of the magmas, whereas low-Mg# magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling, which supplies heat flux to the lower crust. The data also suggest that the mafic lower continental crust beneath the region was thickened between the Late Cretaceous and the Late Paleocene and delaminated during Late Paleocene to Early Eocene time, which coincides with the initial stage of crustal thinning caused by crustal extensional events in the Eastern Pontides and rules out the possibility of an extensional regime before ~ 50 Ma in the region during the Late Mesozoic to Early Cenozoic.
- MakaleAçık Erişim2010Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harşit Pluton, Eastern Turkey
Karsli, Orhan; Dokuz, Abdurrahman; Uysal, Ibrahim; Aydin, Faruk; Chen, Bin; Kandemir, Raif; Wijbrans, Jan
We present elemental and Sr-Nd-Pb isotopic data for the magmatic suite (~79 Ma) of the Harşit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO2 = 59.43-76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO2 = 54.95-56.32 wt%), and exhibits low Mg# (<46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb)n = 2.40-12.44] and display weak Eu anomalies (Eu/Eu* = 0.30-0.76). The rocks are characterized by enrichment of LILE and depletion of HFSE. The Harşit host rocks have weak concave-upward REE patterns, suggesting that amphibole and garnet played a significant role in their generation during magma segregation. The host rocks and their enclaves are isotopically indistinguishable. Sr-Nd isotopic data for all of the samples display ISr = 0.70676-0.70708, εNd(79 Ma) = -4.4 to -3.3, with TDM = 1.09-1.36 Ga. The lead isotopic ratios are (206Pb/204Pb) = 18.79-18.87, (207Pb/204Pb) = 15.59-15.61 and (208Pb/204Pb) = 38.71-38.83. These geochemical data rule out pure crustal-derived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir-Ankara-Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr-Nd isotope modeling shows that the generation of these magmas involved ~65-75% of the lower crustal-derived melt and ~25-35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar-Ar plateau age on hornblende, combined with regional studies, imply that the Harşit pluton formed in a subduction setting and that the back-arc extensional period started by least ~79 Ma in the Eastern Pontides.
- MakaleYalnız künye2009Lithostratigraphy, facies, and deposition environment of the lower Jurassic Ammonitico Rosso type sediments (ARTS) in the Gümüşhane area, NE Turkey: Implications for the opening of the northern branch of the Neo-Tethys Ocean
Kandemir, Raif; Yilmaz, Cemil
Ammonitico Rosso type sediments (ARTS) form the bottom level of the Şenköy Formation in the Gümüşhane area. The formation accumulated in the rift-related basins triggered by extensional tectonic regimes in the Early Jurassic times. Six different sections were studied in this area in order to interpret the lithostratigraphy, facies, and deposition environments of the ARTS. Two basic lithofacies were distinguished, nodular-marly and nodular-calcareous. These facies provide useful information regarding depositional conditions in the area and environmental energy. These factors were mainly related to the relative sea-level that in turn was controlled by tectonic and eustasy conditions. In addition, seven different types of microfacies were recognized and described as a result of the detailed analysis of the sections. The results of the analysis show that these sediments in the Gümüşhane area were developed in transgressive phases/events. These sediments share characteristics with other peri-Mediterranean regions and sea-level curves, and show a similarity to the major transgressive pulse during the Pliensbachian stage. Deposition of ARTS was controlled by syn-depositional extensional movements, leading to their accumulation on top of tilted blocks, slopes and horsts in an open marine environment. The ARTS were developed during the rifting of the continental margins pointing up the phases of the Tethys opening. Neptunian dykes verifying this opening developed at different levels of the ARTS and were filled with overlying sediments. These results support the hypothesis that the ARTS were formed in tectonically active environments where extensional tectonic movements were continuously improved during the deposition of the ARTS.
- MakaleYalnız künye2008The rift-related Late Cretaceous drowning of the Gümüşhane carbonate platform (NE Turkey)
Yilmaz, Cemil; Carannante, Gabriele; Kandemir, Raif
In the Gümüşhane region (NE Turkey), carbonate platform and basin deposits, crop out with excellent exposures. In this area, two localities (Mescitli-İkisu region, 10 km west of the Gümüş hane and Kale-Kilop region, 20 km southeast of the Gümüşhane), in which the related successions are particularly well exposed, have been studied in detail. The outcropping shallow water limestones of the Berdiga Formation (Eastern Pontides Carbonate Platform) were deposited during Late Jurassic-Cenomanian p.p. times in peritidal environments. The overlying Kermutdere Formation consists of monogenic breccias, calciturbidites, red pelagic limestone and siliciclastic turbidites, which were deposited in slope and basin environments. In the Gümüşhane region, the above Formations record the evolution from platform to basin settings in relation to an extensional regime set up in the Cenomanian. The tectonics-related drowning of the Eastern Pontides carbonate platform resulted in graben-semi graben basins in which deep marine sediments were deposited during Late Cretaceous times, having a wedge geometry.
- MakaleYalnız künye2008Elemental and Sr-Nd-Pb isotopic geochemistry of the most recent Quaternary volcanism in the Erzincan Basin, Eastern Turkey: framework for the evaluation of basalt-lower crust interaction
Karsli, Orhan; Chen, Bin; Uysal, Ibrahim; Aydin, Faruk; Wijbrans, Jan R.; Kandemir, Raif
Whole-rock geochemical and Sr, Nd and Pb isotope data are presented for a representative suite of the Quaternary Erzincan Volcanics (QEV) from the Erzincan basin (EB) along the North Anatolian Fault Zone, aiming to understand their origin and implications for basalt-lower crust interaction. Unspiked K-Ar and 40Ar/39Ar dating of dome lavas from the QEVs yielded ages of 102 ± 2 to 1061 ± 88 ka. The QEVs range from high-K low silica trachy-andesite to rhyolite in composition, with rhyolite volumetrically the most abundant. All rocks show high-K calc-alkaline affinity, a geochemical signature common to many post-collisional magmas. They are characterized by enrichment in LILE (Rb, Ba, K, Th) and LREE ((La/Yb)CN = 3-33), with pronounced depletion of HFSE. All lavas show negligible or small negative Eu anomalies in the andesitic to dacitic and strong Eu anomalies in the rhyolitic samples. These rocks have relatively low 87Sr/86Sr = 0.70404-0.70587 and slightly depleted Nd isotopic compositions (εNd from - 0.9 to 2.8), with significantly varied Mg# ranging from 2 to 53. Pb isotopic compositions [206Pb/204Pb = 18.90-19.02, 207Pb/204Pb = 15.64-15.70, 208Pb/204Pb = 38.91-39.97] reveal an enriched source signature, which implies that some portions of metasomatized lithospheric mantle could have contributed to their genesis. The isotopic ratios and chemical features along with the textural and compositional disequilibrium of the plagioclases and amphiboles suggest that mixing of mafic and felsic magmas played an important role in the magma genesis. A possible scenario for the genesis of these volcanic rocks is that basaltic magma formed as a result of partial melting of a subcontinental lithospheric mantle source responding to a possible upwelling of asthenospheric mantle which was caused by the extension produced by strike-slip tectonics. Underplating of these high-temperature basaltic magmas sparked partial fusion of a juvenile lower continental crust producing felsic melts; then magma mixing between basaltic and the felsic magmas followed. Fractional crystallization, with minor amounts crustal contamination could have played an important role in the evolution of magma. Modelling based on Sr and Nd isotope data shows that less than 10% of a basic magma and about 90% of juvenile lower continental crustal material was involved in the generation of the QEVs in a pull-apart basin along the North Anatolian Fault Zone.
- MakaleYalnız künye2006Sedimentary records of the extensional tectonic regime with temporal cessation: Gümüşhane Mesozoic Basin (NE Turkey)
Yilmaz, Cemil; Kandemir, Raif
The Gümüşhane Mesozoic Basin is characterized by Lower-Middle Jurassic volcanic-siliciclastic sediments (Şenköy Formation), Upper Jurassic-Cenomanian platform carbonates (Berdiga Formation) and Upper Cretaceous turbidites (Kermutdere Formation). Four extensional periods (Lias-Dogger, Turonian-Coniacian, Late Campanian (?) and Early (?) Maastrichtian) separated by two quiet tectonic periods (early Malm-Cenomanian and Santonian-Campanian) have been defined in this sequence. The previous studies suggested that Mesozoic basins only formed by extensional movements in the middle Cretaceous. Three extensional periods seperated by two quiet periods from the Cenomanian to the end of the Maastrichtian in Gümüşhane and NE Turkey were firstly proved by sedimentological findings in this study. The definition of these periods depends on features such as (1) neptunian dykes in different levels, (2) shallow marine limestone, (3) thinning-and-fining-upward sequences, (4) mixed faunal assemblages, (5) micro-turbiditic structures, (6) syn-sedimentary fault, (7) grabens, half-grabens, (8) pelagic limestone, (9) calciturbidites, (10) laterally and vertically rapid changes of the thickness and facies, (11) platform-to-basin transition and (12) monogenic breccias.