GD Anadolu Orojenik Kuşağı ofiyolitlerinin manto peridotitleri bileşimleri ve petrolojisi: Ana element, iz element jeokimyası ve mineral kimyası

The aim of this study is to reveal mantle processes such as tectonic environment, partial melting degree and melt-rock interactions of mantle peridotite (harzburgite and dunite) of Kızıldağ, Koçali and Guleman ophiolites outcropping in South Eeast Anatolia Ophiolite Belt. For this purpose, geochemical analyses of whole rock (main oxide, trace element, Rare Earth Element) and mineral base (mineral chemistry) in mantle peridotite samples which are generally harzburgite and dunite, show different degrees of serpentinization, were carried out in various laboratories. As a result of all of this study, the clinopyroxene minerals of harzburgite and dunite type rocks belonging to the mantle peridotites of the ophiolites are extremely depleted. So it seems that these samples have very low Al2O3 (% 0−4,93 %wt.) and CaO (%0.10−2.38 %wt.) and high MgO (39.27−49.58 %wt.) content in whole rock. In addition, the fact that these rocks have high Cr# in spinels is interpreted because the mantle peridotites contain moderate to high degrees of partial melting residues. On the other hand, enrichment of Al2O3 and CaO contents and decrease of Cr# values of spinels in proportion to increasing clinopyroxene abundances of some mantle peridotite samples result from lower degree melting residues than other samples. Enrichment of mantle peridotites, especially light REE and Large Ion Lithophile Elements (LILE), is a result of metasomatism with melts having different composition in subduction zones. As a result, especially considering the results of mineral chemistry, trace element and RRE analysis, it is thought that the mantle peridotites of the ophiolites are the residual rocks which form the subject of the project are formed in the mid-ocean ridge environment and then exposed to the second phase depletion in the subduction zone (forearc environment) and in this period, it is thought that metasomatized by slab derived melt in various composition

A forearc (Guleman, Elaziğ) ophiolite: Evidence from peridotite mineral geochemistry

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

Zircon U-Pb age and geochemical constraints on the origin and tectonic implication of Cadomian (Ediacaran-Early Cambrian) magmatism in SE Turkey

The Bitlis-Pütürge Massifs and Derik volcanics that crop out in the Southeast Anatolian Belt are parts of the Cadomian domain in Anatolia where relicts of the oldest continental crust of Turkey are exposed. The Bitlis-Pütürge Massifs contain a Neoproterozoic basement, with overlying Phanerozoic rocks that were imbricated, metamorphosed and thrust over the edge of Arabia during the Alpine orogeny. The basement consists mainly of granitic to tonalitic augen gneisses and metagranites, associated with schists, amphibolites and paragneisses. Based on whole-rock geochemical data, the augen gneisses are interpreted to have protoliths crystallized from subduction zone magmas. This study conducted the first zircon dating on two augen gneisses that gave 206Pb/238U dates of 551 ± 6 and 544 ± 4 Ma, interpreted as the formation ages of the Pütürge Massif, broadly coeval to those of the Bitlis metagranites and the Derik volcanics that occurred from ca. 581 to 529 Ma (the Ediacaran-early Cambrian). The eHf(t) values (+1.2 to 5.3) of the dated zircons, with crustal model ages (TDM C ) from 1.4 to 1.8 Ga, indicate that formation of the Pütürge Massif involves an older, most likely the Mesoproterozoic, continental crust component. Similar to the Bitlis-Pütürge gneisses, coeval basement rocks are widespread in the Tauride-Anatolide platform (e.g., the Menderes Massif). All these dispersed Cadomian basement rocks are interpreted as fragments of the Ediacaran-Early Cambrian continental arcs bordering the active margin of northern Gondwan

A forearc (Guleman, Elaziğ) ophiolite: Evidence from peridotite mineral geochemistry

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

A forearc (Guleman, Elaziğ) ophiolite: Evidence from peridotite mineral geochemistry

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

Zircon U-Pb age geochemical constraints on the origin and tectonic implication of late cretaceous arc-type magmatism in Pertek region (Tunceli, East Turkey)

The plutonic units of the Elazıg Magmatics crop out in the Pertek-Tunceli (Turkey) region in the Southeast Anatolian Orogenic Belt. This study reports geochemical data, Sr-Nd isotope ratios and U-Pb zircon age of the Late Cretaceous granitoids. Granitoids belonging to Elazıg Magmatics consist of tonalite, granodiorite, monzogranite, gabbro, diorite, monzodiorite and quartz monzodiorite. Geochemically, they have SiO2=45.56-76.03%, MgO=0.07-8.99%, Mg# =8.7- 75.4 and Al2O3=12.19-23.76%. Geochemical analyzes suggest that granitoids are peralüminous and I type and vary from low-K tholeiitic to shoshonitic in composition. The result of LA-ICP-MS U-Pb zircon dating revealed that these granitoids formed, in the Late Cretaceous (77.2±1.1-80.6±0.9 Ma). Trace element patterns normalized primitive mantle and chondrite normalized REE indicate that in LREE relating to HREE and in LILE relating to HFSE have enrichments. (87Sr/86Sr)i values of these rocks vary between 0.7039 and 0.7072 in the compositions. On the other hand, ƐNdi is between -1.7 and 6.7. Therefore, the variation is indicative of changing in the source components in the Elazıg Magmatism that we attribute to tectonic switching from an intra-oceanic subduction setting to a collision with the Arabian continent in the region

Mineral chemistry and petrology of mantle peridotites from the Guleman Ophiolite (SE Anatolia, Turkey): Evidence of a forearc setting

The Guleman ophiolite situated in SE Anatolia, Turkey is regarded as a fragment of Late Cretaceous oceanic lithosphere, consisting a core of mantle rocks overlain by an ultramafic sequence, layered and isotropic gabbros, sheeted dykes structurally overlies the Lower Miocene Lice Formation and is depositionally overlain by sandstones and shales of the Upper Maashtrichtian-Lower Eocene Hazar complex and Middle Eocene Maden Complex (Righo de Righi and Cortesini, 1964; Erdogan, 1977; Perinçek, 1979; Özkaya, 1978; Perinçek, and Çelikdemir, 1979; Bingöl, 1986; Beyarslan and Bingöl, 2014). The mantle peridotites consist mainly of fresh and in place serpentinized harzburgites with local bands and lenses of dunite and large-sized chromitite pods. The harzburgites contain 70-80 modal % of olivine and 15-25 modal % of orthopyroxene. The minor phases are clinopyroxene (2-3 modal %) and chrome-spinel (2-3 modal %). They commonly display high-temperature deformation fabrics such as kink-bands in olivines. The main texture of the harzburgites is porphyroclastic texture, and occasionally mylonitic textures can be observed. Orthopyroxene and spinel are stretched in some samples. Chrome-spinel exhibits vermicular and xenomorphic, and rarely idiomorphic habits in peridotites. They contain 2-3% clinopyroxene as exsolution lammelles in orthopyroxene. The harzburgite and dunite have low CaO and Al2O3 abundances similar to Mariana fore-arc peridotite (Pearce et al. 1992). The average Cr-ratio = (Cr/(Cr + Al) atomic ratio) of Cr-spinels in harzburgites, and dunites is remarkably high (>0.63). The Fo content of olivine is between 90.9 to 92.3 in harzburgites and dunites. In the Mg# (Mg/(Mg+Fe2+)) versus Cr# in spinel diagram used to determine the degree of partial melting and the tectonical environment, the spinel plot in the forearc peridotites field and the degree of the partial melting is > 35% (Fig.1). Orthopyroxene and clinopyroxene lammelles from the Guleman harzburgites have low CaO, Al2O3 and TiO2 contents, resembling those of depleted harzburgites from modern fore-arcs and different from moderately depleted abyssal peridotites. Fore-arc peridotites are typically more depleted than abyssal peridotites, except for some lherzolites from the South Sandwich forearc (Arai and Ishimaru, 2008; Pearce et al. 2000). In fertile abyssal lherzolites, spinels with Cr#< 30 are dominant (Dick and Bullen, 1984), while spinel in fore-arc peridotites may cover a slightly wider range, 40 < Cr# < 80 (Arai, 1994). The unusually depleted nature of forearc peridotites requires unusual melting conditions: abnormally high temperature, volatile flux, or both. Higly depleted harzburgites, dunites and chromitites in the ophiolites form by melts of the mantle wedge overlying the new subduction zone (Shervais, 2001). These melts form in response to continued melting of previously depleted asthenosphere brought about by increasing flux of fluids and melts from the subducting slab (Shervais, 2001). According to Whattam and Stern (2011), most ophiolites are fragments of exhumed forearcs and that forearcs form during subduction initiation allows us to use ophiolites to explore how subduction zones form. 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

Zircon U-Pb age and geochemical constraints on the origin and tectonic implication of Cadomian (Ediacaran-Early Cambrian) magmatism in SE Turkey

The Bitlis-Pütürge Massifs and Derik volcanics that crop out in the Southeast Anatolian Belt are parts of the Cadomian domain in Anatolia where relicts of the oldest continental crust of Turkey are exposed. The Bitlis-Pütürge Massifs contain a Neoproterozoic basement, with overlying Phanerozoic rocks that were imbricated, metamorphosed and thrust over the edge of Arabia during the Alpine orogeny. The basement consists mainly of granitic to tonalitic augen gneisses and metagranites, associated with schists, amphibolites and paragneisses. Based on whole-rock geochemical data, the augen gneisses are interpreted to have protoliths crystallized from subduction zone magmas. This study conducted the first zircon dating on two augen gneisses that gave 206Pb/238U dates of 551 ± 6 and 544 ± 4 Ma, interpreted as the formation ages of the Pütürge Massif, broadly coeval to those of the Bitlis metagranites and the Derik volcanics that occurred from ca. 581 to 529 Ma (the Ediacaran-early Cambrian). The eHf(t) values (+1.2 to 5.3) of the dated zircons, with crustal model ages (TDM C ) from 1.4 to 1.8 Ga, indicate that formation of the Pütürge Massif involves an older, most likely the Mesoproterozoic, continental crust component. Similar to the Bitlis-Pütürge gneisses, coeval basement rocks are widespread in the Tauride-Anatolide platform (e.g., the Menderes Massif). All these dispersed Cadomian basement rocks are interpreted as fragments of the Ediacaran-Early Cambrian continental arcs bordering the active margin of northern Gondwan

Short lived late Cretaceous arc magmatism in SE Turkey: Temporal geochemical variations and tectonic implications

Neotethyan ophiolites that crop out in the northern margin of Arabia, from SE Turkey to Iran and Oman, have a short “life span” of <20 myr from their birth to death. While this ophiolite belt is widely believed as forming in the forearc environment related to intra-oceanic subduction initiation, the arc magmatic product is rarely observed in this belt. Here we report for the first time zircon U-Pb ages and Hf isotopes, and whole-rock geochemical and Sr-Nd-Hf isotopic data of late Cretaceous (83-73 Ma) magmatic rocks from the areas around Elazığ, SE Turkey, which we argue to be part of the missing arc product subsequent to the formation of the ophiolites. The Elaziğ magmatics that occurred within a short period (~10 myr) are characterized by significant geochemical variations over time, varying from low- K tholeiitic to calc-alkaline and then shoshonitic, with associated enrichments in LREE and LILE, and progressive changes in isotopic compositions. Zircon and whole-rock εHf(T) values, for example, vary from +20 to -3. The temporal variations are interpreted as involving two main components in the magma generation, i.e., a depleted mantle source that prevails in the formation of the Neotethyan ophiolites and an old continental crust that resembles the Bitlis- Puturğe massif in SE Turkey. Moreover, the variations are indicative of changing source regions of the Elazığ magmatism that we attribute to the collision and following continental subduction of Arabian crust, thus resulting in the HP-LT metamorphism of the Bitlis-Puturğe massif during 79-74 Ma. To sum up, the Elazığ magmatism, shortlived in the late Cretaceous while showing significant geochemical variations, suggests a rapid switching of tectonic setting from intra-oceanic subduction to continental collision, a common feature in the Arabia-Eurasia collision zone marked with the “Turkic-type” orogeny