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- Doktora TeziAçık Erişim2022Eosen yaşlı Kazıkbeli plütonu'nun (Kürtün-Gümüşhane) petrografisi,petrokimyası, U-Pb zirkon jeokronolojisi,tüm-kayaç Sr-Nd-Pb ve zirkon Lu-Hf izotop jeokimyası ve petrolojisi
Zikrullah Samet Güloğlu
Bu çalışmada, Doğu Pontidler'in kuzeyinde Kürtün (Gümüşhane) yöresinde yer alan Kazıkbeli Plütonu'nun petrografisi, mineral kimyası, zirkon U-Pb jeokronolojisi, tüm-kayaç ve Sr-Nd-Pb izotop jeokimyası ile zirkon Lu-Hf izotop jeokimyası verileri kullanılarak petrolojisi irdelenmiştir. Kazıkbeli Plütonu KD-GB uzanımlı olup, yaklaşık 46 km2 lik bir alanda yayılım gösterir. Plütonu oluşturan kayaçların bileşimleri gabroyik diyoritten granite kadar değişmekte olup, başlıca mineralleri plajiyoklas (An25-65), ortoklas (Or1-3), kuvars, amfibol (Mg#=0.63-0.73), biyotit (Mg#=0.52-0.58) ve Fe-Ti oksitler oluşturur. LA-ICP-MS U-Pb zirkon yaşlandırmasına göre plütonu oluşturan kayaçların kristalizasyon yaşları gabroyik diyoritler için 46.06 ± 0.24 My ve granodiyoritler için 45.55 ± 0.26 My olup, Lütesiyan (orta Eosen) dönemine karşılık gelmektedir. Kazıkbeli Plütonu I-tipi, yüksek K'lu kalk-alkali, genellikle metalümin az oranda da peralümin karakterlidir. Ana ve iz element değişimleri, kayaçların gelişiminde plajiyoklas, amfibol ve Fe-Ti oksit fraksiyonlaşmasının etkili olduğunu göstermektedir. Kayaçların εNd(i) değerleri 1.85-2.24, 87Sr/86Sr(i) değerleri ise 0.70458-0.70484 arasındadır. Kayaçların 206Pb/204Pb(i), 207Pb/204Pb(i) ve 208Pb/204Pb(i) içerikleri sırasıyla 18.50-18.57, 15.60-15.61 ve 38.56-38.59 arasındadır. Kayaçların εHf(i) değerleri 5.75-8.03 arasında değişmektedir. Tüm veriler, incelenen plütonik kayaçların ana magmasının litosferik mantodan türediğini, kabuksal kayaçların katkısının nispeten az olduğunu göstermektedir. İncelenen kayaçların kristallenmeleri esnasındaki katılaşma sıcaklıkları (706-828 °C), basınçları (0.6–0.9 kbar) ve oksijen fugasitesi (ƒO2) değerleri (-12.5 ile -13.8) birbirine oldukça yakındır. Tüm bu veriler Kazıkbeli Plütonunu oluşturan kayaçların nispeten sığ derinliklere yerleşmiş olduklarını ifade eder.
- MakaleAçık Erişim2011Transition from shoshonitic to adakitic magmatism in the eastern Pontides, NE Turkey: Implications for slab window melting
Eyuboglu, Yener; Chung, Sun-Lin; Santosh, M.; Dudas, Francis O.; Akaryali, Enver
The formation of the eastern Pontides orogenic belt has been widely assigned to a northward subduction of the Neotethyan oceanic slab during the late Mesozoic-Cenozoic. Here we provide an alternate model based on new geological, geochemical and isotopic data. The magmatic activity in the far south of the belt started in the early Campanian with shoshonitic trachyandesites and associated pyroclastics. This sequence is covered by the late Campanian-early Maastrichtian reefal limestones and another stage of high-K volcanism represented by analcimized leucite-rich ultrapotassic rocks of the Maastrichtian-early Paleocene (?) ages. The shoshonitic and ultrapotassic rocks, with K2O contents ranging from 0.26 to 6.95 wt.%, display broadly similar rare earth and multi-element distribution patterns. Both rock types are enriched in LILE and LREE and depleted in HFSE (Nb,Ta and Ti), suggesting a subduction-enriched mantle source for the magma generation. Subsequently, during the late Paleocene, a stage of acidic magmatism (SiO2 of 53.25-73.61 wt.%) that shows adakitic geochemical characteristics including high Sr/Y (46-416) and La/Yb (11-51) and low Y (2.6-12.2 ppm), is documented characterized by melting of a mafic source such as the MORB crust with garnet in the residue. The adakitic magmatism began at similar to 56 Ma and migrated toward the north through time, culminating with porphyritic andesites (similar to 47 Ma) that were emplaced in the Gumushane-Bayburt line and its vicinity. North of this line, coeval magmas show typical calc-alkaline nature and continued to develop toward further north until the middle to late Eocene. Based on the spatial and temporal variations in the magmas generated in the eastern Pontides orogenic belt, we propose a new geodynamic model to explain the tectonomagmatic evolution of these rocks and correlate the adakitic magmatism to ridge subduction and slab window process within a south-dipping subduction zone. Our model is in contrast to the previous proposals which envisage partial melting or delamination of thickened lower continental crust due to the collision in the south during the Paleocene-Eocene. (C) 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
- MakaleYalnız künye2011Migrating magmatism in a continental arc: Geodynamics of the Eastern Mediterranean revisited
Eyuboglu, Yener; Santosh, M.; Dudas, Francis O.; Chung, Sun-Lin; Akaryali, Enver
The eastern Pontide orogenic belt in Turkey offers a critical region to evaluate the geodynamic evolution of the eastern Mediterranean region during the late Mesozoic-Cenozoic. Here we synthesize results from our exhaustive database on the geochemical characteristics of adakitic magmatism from 137 bodies covering 7 domains in the southern zone of eastern Pontides. Together with new Pb-Sr-Nd results, we show that the adakitic magmatism in the eastern Pontide belt is clearly linked to slab window processes during ridge subduction, as against the earlier models that assumed partial melting of a delaminated or thickened lower continental crust following collision. The isotopic compositions display a complex pattern and suggest mixing of multiple source materials such as depleted mantle, enriched lithospheric mantle, and upper crust. We also confirm a southward polarity of subduction as against the previous models that assumed a northward subduction. We supplement our model with evidence for a northward propagation of the adakitic magmatism, spatial and temporal variations in arc magmatism, presence of south-dipping reverse faults and a synthesis of the available paleomagnetic data. Our studies also suggest that the Black-Sea is a remnant of the Tethyan ocean that was situated to the north of the arc during the late Mesozoic-Cenozoic as against the correlation to a late Mesozoic-Cenozoic back-arc basin related to a northward subduction of the Paleo- or Neo-tethyan oceanic lithosphere in alternate models. (C) 2010 Elsevier Ltd. All rights reserved.