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- MakaleYalnız künye2022From Cadomian back-arc basin to Rheic Ocean closure: the geochronological records of the Kurtoglu Massif, eastern Sakarya Zone, Turkey
Dokuz, Abdurrahman; Gücer, Mehmet Ali; Karsli, Orhan; Yi, Keewook
New U-Pb zircon data from the Kurtoglu Massif (eastern Sakarya Zone, Turkey) reveal a Cadomian back-arc basin, evolving to closure of the Rheic Ocean. A host metapsammite from the lower tectonic slice of the massif yielded detrital zircon ages ranging from Neoarchean (2.73 Ga) to late Neoproterozoic with a major population between 610 and 553 Ma and a peak at 592 Ma, implying that the basement of the Sakarya Zone has a Cadomian affinity. This metasedimentary sequence was intruded by an orthogneiss in the early Ordovician (481 Ma) probably during the opening of the Rheic Ocean. Zircon grains from the overlying metasedimentary sample yielded concordant ages spreading throughout the Mesoproterozoic (1608-1032 Ma) and early Paleozoic (516-351 Ma), suggesting that they were deposited in the Rheic Ocean likely prior to its final closure. The muscovite metagranite, emplaced into the host rocks of the Kurtoglu Massif at 388 Ma, formed probably during northward closure of the Rheic Ocean. Zircon grains of a metasiltstone from the upper tectonic slice of the massif, represented mainly by phyllites, yielded similar age spectra to that of the host metapsammite of the lower tectonic slice. Such phyllites in the Pulur Massif similar to 35 km to the southeast display a close association with the ophiolitic complexes of the Rheic Ocean. This relationship together with the age spectra mentioned above suggests that sedimentation was on a place away from the Paleozoic igneous sources, in an analogous position to the southern passive margin of the Rheic Ocean.
- MakaleAçık Erişim2022Petrogenesis of post-collisional Middle Eocene volcanism in the Eastern Pontides (NE, Turkey): Insights from geochemistry, whole-rock Sr-Nd-Pb isotopes, zircon U-Pb and 40Ar-39Ar geochronology
Aydınçakır, Emre; Yücel, Cem; Ruffet, Gilles; Gücer, Mehmet Ali; Akaryalı, Enver; Kaygusuz, Abdullah
The debate about whether Eocene magmatism is considered to be post-collisional or subduction-related or not still continues. Here we offer new 40Ar-39Ar ad U-Pb zircon geochronology, mineral chemistry, bulk rock and Sr-Nd-Pb isotope geochemistry data obtained from the southern dike (SD) suite, in comparison with the northern dike (ND) suite, from the Eastern Pontides. The geochronological data indicate that the SD suite erupted between 45.89 and 45.10 Ma corresponding to the Lutetian (Middle Eocene). The magmas of the ND suite are characterised by slightly more alkaline affinity compared to the SD suite. The trace and rare earth element (REEs) content of the SD suite is characterised by large ion lithophile element (LILEs; Sr, K2O, Ba, Rb) enrichment and depletion of Nb, Ta, and TiO2 elements to different degree with high Th/Yb ratios, which indicate that the magmas forming the SD and ND suites were derived from lithospheric mantle sources enriched by mostly slab-derived fluids in the spinel stability field. The Sr, Nd and Pb radiogenic isotope ratios of the dikes support the view that the magma for the hydrous group (H-SD) was derived from a relatively more enriched mantle source than the other SD and ND suites. The ND suite and the anhydrous group (A-SD) display similar geochemical features characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios, while the H-SD group has respectively lower LREE/HREE ratios indicating higher melting degree. Detailed considerations of the alkalinity, enrichment and partial melting degree for the source of the studied volcanic rocks indicate that the magmas of the northern dike suite are characterised by slightly more alkaline affinity, whereas the magmas throughout the southern dike suite show increments in the enrichment rate and melting degree. In light of the obtained data and comparative interpretations, the geodynamic evolution and differences in petrogenetic character of the Lutetian magmas from both the northern and southern parts of the Eastern Pontides may be explained by different degrees of melting of a net veined mantle source initially metasomatized by mostly subduction fluids during asthenospheric upwelling due to fragmented asymmetric delamination in a post-collisional extensional tectonic environment.
- MakaleYalnız künye2013Petrogenesis and U-Pb zircon chronology of adakitic porphyries within the Kop ultramafic massif (Eastern Pontides Orogenic Belt, NE Turkey)
Eyuboglu, Yener; Dudas, Francis O.; Santosh, M.; Yi, Keewook; Kwon, Sanghoon; Akaryali, Enver
High-silica adakites intrude the Kop ultramafic massif in the eastern Pontide orogenic belt of NE Turkey. These dominantly dacitic to rhyodacitic plagioclase porphyries form clusters of small intrusions. U-Pb dating of zircons from two intrusions yields ages between 52 and 59 Ma. The best-constrained crystallization age is 55.83 +/- 0.04 Ma, indicating that these are the oldest adakitic rocks of the eastern Pontides. The rocks show geochemical signatures typical of adakites. The absence of systematic geochemical variation within the adakite suite indicates a subordinate role for fractional crystallization and binary mixing, and suggests that individual intrusions may represent separate, small batches of magma. Modeling of partial melting suggests that the degree of melting was 5-20%, that the residues after melting likely contained garnet, clinopyroxene, and rutile, and that plagioclase was either absent or totally consumed during partial melting. The most likely source compositions had large-ion lithophile elements >10 times, and heavy rare earth elements <10 times, chondritic concentrations. Modeled bulk distribution coefficients indicate that the adakites were generated as silicic magmas, and are not derived by fractional crystallization from basaltic or andesitic parental melts. Sr, Nd, and Pb isotopic data indicate at least three isotopically distinct sources, one of which is depleted mantle. The other components include upper crust (possibly a mixture of subducted sediment and Hercynian continental basement rocks) and a component that may include both lower crust and sublithospheric mantle. These adakites are unique among the late Cretaceous and Cenozoic igneous rocks of the eastern Pontides in having a large proportion of the depleted mantle component. The prominent role of the depleted mantle in their petrogenesis suggests that the adakites may be related to a slab window in a south-directed subduction zone. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
- MakaleYalnız künye2011Crystal fractionation of adakitic magmas in the crust-mantle transition zone: Petrology, geochemistry and U-Pb zircon chronology of the Seme adakites, eastern Pontides, NE Turkey
Eyuboglu, Yener; Santosh, M.; Chung, Sun-Lin
Plutonic and porphyritic intrusions of adakitic rocks are widely distributed in the southern part of the eastern Pontides orogenic belt in Turkey. Ranging in age from late Paleocene to early Eocene, these intrusions provide critical information to evaluate the early Cenozoic geodynamic evolution of the eastern Mediterranean region. Here we report the results from our field, petrologic, geochemical and zircon U-Pb geochronological studies on adakitic intrusions in the Seme area from the southern part of eastern Pontides belt. The Seme granitoid, Daldibi dacite and Aslanca dacite porphyry from this region carry abundant plagioclcase, amphibole and biotite phenocrysts and have geochemical affinities typical of adakites including high SiO2 (58.48-75.6wt.%), Al2O3 (15.78-18.28wt.%), Na2O (3.94-5.08wt.%), Sr (506-1413ppm), and La (12.6-52.9ppm), moderate K2O (1.77-2.76wt.%), and low Y (4.7-14.2ppm) and Yb (0.28-1.29ppm). The early Eocene intrusions in the Seme area have compositional similarities with high-slica adakites, and their geochemical features suggest the involvement of slab-derived melts. The zircons separated from these rocks show euhedral crystal shapes with oscillatory cores typical of crystallization from magmas, as also confirmed by their high Th/U ratios (0.78 to 1.15). U-Pb analyses of zircons from the quartz diorite yielded a weighted mean 206Pb/238U age of 53.16±0.45Ma. Zircon grains from the Aslanca dacite porphyry occurring as a late phase within the Seme body show U-Pb isotopic ages of 53 and 52Ma concordant with U-Pb ages of zircons from quartz diorite. Based on major, trace and rare earth element data, we present a model suggesting crystal fractionation and/or differentation processes of subduction-related adakitic magmas stored in the crust-mantle transition zone, and their transfer into shallow depths of the overriding continental lithosphere.