The mantle section of Guleman ophiolite, southeast (SE) Turkey consists mainly of harzburgites and dunite lenses and large chromitite pods. The average Cr ratio ¼ [100 Â Cr/(Cr þ Al) atomic ratio] of Crspinels in harzburgites and dunites is remarkably high (>63). The forsterite (Fo) content of olivine is between 90.9 and 92.3 in harzburgites and dunites. These features indicate that the harzburgites and dunites resulted from >35% of partial melting of a depleted mantle source. Discriminant geochemical diagrams based on the mineral chemistry of harzburgites indicate a supra-subduction zone (SSZ) origin. Orthopyroxene and clinopyroxene from the Guleman harzburgites have low CaO, Al 2 O 3 and TiO 2 contents, resembling those of depleted harzburgites from modern forearcs and contrasting with moderately depleted abyssal peridotites. Consequently, we propose that the Guleman peridotites formed in a forearc setting during the subduction initiation that developed as a result of northward subduction of the southern branch of the Neo-Tethys in response to the convergence between the Arabian and Anatolian plates.
In this study, the petrographic and geochemical characteristics of Late Cretaceous-Middle Eocene Keban magmatic rocks were examined in Keban-Elazığ. Apart from the Keban Magmatic rocks, the other units outcropping around the region are the Late Devonian-Late Triassic Keban Metamorphics, Paleogene-Neogene sedimentary units and Plio-Quaternary alluviums. The investigated rocks are represented by syenite porphyry and quartzmonzonites belonging to Keban Magmatic rocks, which cut the Keban metamorphic rocks. The Keban Magmatic rocks consist of the main minerals are K-feldspar (mega-phenocrystal), plagioclase, amphibole, biotite and quartz minerals, which shows porphyric, porphyric holocrystalline, poikilitic texture in general. All the samples are shoshonitic in composition and fall into the A-type granitoid region. The tectonic environment of the investigated rocks is post-collisional granites.
Bu çalışma Elazığ Bölgesinde yüzeyleyen Kuvaterner yaşlı Harput volkanik kayaçlarının jeokimyasal ve izotop analizlerinin değerlendirilmesini kapsamaktadır. Sol yönlü doğrultu atımlı olan Doğu Anadolu Fay Zonu (DAFZ) Türkiye'nin en önemli faylarından birisidir. Elazığ bölgesinde DAFZ boyunca mafik alkali özellikte volkanik kayaçlar yüzeylemektedir. Bu volkanik kayaçlar, yüksek LILE ve HFSE içeriklerine ve düşük LILE/HFSE oranlarına (Ba/Nb=2.28-10.7) ve düşük 87 Sr/ 86 Sr (0.703149-0.703915) ve yüksek 143 Nd/ 144 Nd (0.512751-0.512895) oranlarına sahiptirler. Kimyasal bileşimleri levha içi magmaların bileşimlerine benzemektedirler. Yüksek Nb (34-76.6 ppm), ve Nb/La oranları (>1.0) gösterirler. Nb/La oranları lavların kirlenmemiş veya çok az kirlenmiş olduğunu belirtmektedir. Pozitif Sr anomalisi ve Eu anomalisinin olmaması plajiyoklasların esas fraksiyonlaşma mineral fazı olmadığını belirtir. Farklı veriler Harput volkanitlerinin spinel lerzolitin düşük derecede kısmi ergimesi (~% 0.4-4) ile Doğu Anadolu Fay Zonu'na ait fay sistemlerinin kesişme noktalarında oluşmuştur.
The Guleman ophiolite, one of the most important ophiolitic massifs of the Southeast Anatolian Ophiolitic Belt, consists of a core of serpentinized mantle rocks overlain by an ultramafic sequence, layered and isotropic gabbro, and sheeted dykes. The ophiolite structurally overlies the Lower Miocene Lice Formation and is overlain by young sandstones and shales of the Upper Maashtrichtian‐Lower Eocene Hazar Complex and Middle Eocene Maden Complex. The Guleman ophiolite tectonically overlain by Precambrian to Upper Triassic Bitlis metamorphic massif.
The mantle peridotites compose mainly of fresh and in place serpentinized harzburgite tectonite with local bands and lenses of dunites with large‐sized chromitite pods. The Guleman peridotites commonly show porphyroclastic texture, high‐temperature fabrics such as kink‐bands in olivines.
According to microprobe analyses, the harzburgite and dunite have low CaO and Al2O3 abundance similar to Mariana forearc, and their average Cr‐ (=Cr/(Cr+Al) atomic) ratio of Cr‐spinelsis surprisingly high (>0.63) besides Fo content of olivine is between 90.9 to 92.3 in peridotites. According to Mg# (Mg/(Mg+Fe2+)) versus Cr# in spinel diagram, the degree of partial melting is higher than 35% and spinel values plot in the forearc peridotites field. The Gulemanharzburgites have low CaO, Al2O3 and TiO2 contents in orthopyroxene and clinopyroxene lammelles, resembling those of depleted harzburgites from modern forearcs and different from moderately depleted abyssal peridotites.
Consequently, we propose that the Guleman peridotites form in a forearc setting during the subduction initiation that developed as a result of northward subduction of the southern branch of the Neo‐Tethys in response to the convergence between Arabian and Anatolian plates.
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