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- MakaleAçık Erişim2023Geochemical and radiometric data for mafic rocks from the Guleman Ophiolite (SE, Turkey): New insights on the geodynamic evolution of the southern Neo-Tethyan ocean
Sapancı, Özgür; Tokat, Gürkan; Eraslan, Nuh Kadri; Karakaya, Abdullah Onur; Gücer, Mehmet Ali; Çimen, Okay
The Guleman Ophiolite is located in the southeast of Turkey and mainly consists of harzburgites and dunites hosting economically viable chromitite bodies, and lesser amounts of cumulate and isotropic gabbro, diabase dykes, pyroxenite and locally plagiogranite. This study reports the combined whole-rock geochemical and radiogenic isotope (Sr and Nd) data for gabbro and diabase dykes, and in-situ zircon U-Pb geochronological data for plagiogranite and gabbro from the Guleman Ophiolite. Two different geochemical groups were determined based on immobile minor and trace elements, and radiogenic isotope characteristics of gabbro and diabase dykes investigated here. The first group is represented by boninites and displays highly depleted elemental patterns compared to NMORB, and spoon-shaped rare earth element profiles. Contrarily, the second group resembles back-arc basin basalts and is characterized by NMORB-like rare earth element patterns associated with negative Nb anomalies. The boninitic samples are characterized by less radiogenic 143Nd/144Nd(i) (0.51229 to 0.51267; ƐNd = −4.8 to +2.7) and more radiogenic 87Sr/86Sr(i) (0.70549 to 0.70758) isotope compositions compared to the back-arc basin basalt-like samples (143Nd/144Nd(i) = 0.51289 to 0.51296; ƐNd = +7.0 to +8.4; 87Sr/86Sr(i) = 0.70496 to 0.70629), indicating derivation from distinct and/or heterogeneous mantle source regions within a supra-subduction zone. The LA–ICP–MS zircon U-Pb analyses yielded concordant late Cretaceous ages for gabbro (82 ± 2.9 Ma) and plagiogranite (79.9 ± 0.8 Ma) samples. The overall geochemical, isotopic and geochronological data presented here suggest that the Guleman Ophiolite consists of forearc and initial back-arc spreading sections of oceanic crust, which may have been formed in an intra-oceanic subduction zone within the Berit Ocean (northern branch of the southern Neo-Tethyan ocean). Moreover, the generation of continental arc magmatism (i.e. Baskil and Esence Granitoids) was well-documented on the active margin of the Malatya-Keban Metamorphics to the north. Therefore the closure of this oceanic basin should have resulted in multiple coeval northward subduction events during the late Cretaceous.
- 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 künye2007Geochemical and Sr-Nd-Pb isotopic compositions of the Eocene Dölek and Sariçiçek Plutons, Eastern Turkey: Implications for magma interaction in the genesis of high-K calc-alkaline granitoids in a post-collision extensional setting
Karsli, Orhan; Chen, Bin; Aydin, Faruk; Şen, Cüneyt
The major and trace elements and Sr-Nd-Pb isotopes of the host rocks and the mafic microgranular enclaves (MME) gathered from the Dölek and Sariçiçek plutons, Eastern Turkey, were studied to understand the underlying petrogenesis and geodynamic setting. The plutons were emplaced at ∼ 43 Ma at shallow depths (∼ 5 to 9 km) as estimated from Al-in hornblende geobarometry. The host rocks consist of a variety of rock types ranging from diorite to granite (SiO2 = 56.98-72.67 wt.%; Mg# = 36.8-50.0) populated by MMEs of gabbroic diorite to monzodiorite in composition (SiO2 = 53.21-60.94 wt.%; Mg# = 44.4-53.5). All the rocks show a high-K calc-alkaline differentiation trend. Chondrite-normalized REE patterns are moderately fractionated and relatively flat [(La/Yb)N = 5.11 to 8.51]. They display small negative Eu anomalies (Eu/Eu* = 0.62 to 0.88), with enrichment of LILE and depletion of HFSE. Initial Nd-Sr isotopic compositions for the host rocks are εNd(43 Ma) = - 0.6 to 0.8 and mostly ISr = 0.70482-0.70548. The Nd model ages (TDM) vary from 0.84 to 0.99 Ga. The Pb isotopic ratios are (206Pb/204Pb) = 18.60-18.65, (207Pb/204Pb) = 15.61-15.66 and (208Pb/204Pb) = 38.69-38.85. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with ISr ranging from 0.70485 to 0.70517, εNd(43 Ma) - 0.1 to 0.8 and with Pb isotopic ratios of (206Pb/204Pb) = 18.58-18.64, (207Pb/204Pb) = 15.60-15.66 and (208Pb/204Pb) = 38.64-38.77. The MMEs have TDM ranging from 0.86 to 1.36 Ga. The geochemical and isotopic similarities between the MMEs and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas. All the geochemical data, in conjunction with the geodynamic evidence, suggest that a basic magma derived from an enriched subcontinental lithospheric mantle, probably triggered by the upwelling of the asthenophere, and interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on the Sr-Nd isotope data indicates that ∼ 77-83% of the subcontinental lithospheric mantle involved in the genesis. Consequently, the interaction process played an important role in the genesis of the hybrid granitoid bodies, which subsequently underwent a fractional crystallization process along with minor amounts of crustal assimilation, en route to the upper crustal levels generating a wide variety of rock types ranging from diorite to granite in an extensional regime.