Sources and petrogenesis of Jurassic granitoids in the Yusufeli area,Northeastern Turkey: Implications for pre- and post-collisional lithospheric thinning of the eastern Pontides |
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| Authors: | Abdurrahman Dokuz Orhan Karsli Bin Chen ?brahim Uysal |
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| Affiliation: | 1. School of Earth Sciences, Damghan University, Damghan 36716-41167, Iran;2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, PR China;3. Geosciences Dept., University of Texas at Dallas, Richardson, TX 75083-0688, USA;4. Geobiotec, Departamento de Geociências, Universidade de Aveiro, 3810-193 Aveiro, Portugal;5. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, PR China;1. Department of Geological Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey;2. Journal Center, China University of Geosciences, 29 Xueyuan Road, Beijing 100083, China;3. Korea Basic Science Institute, YangCheong 804-1, Ochang, Cheongwon, Chungbuk 363-883, South Korea;4. Department of Geological Engineering, Gumushane University, 29000 Gumushane, Turkey;5. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;1. Department of Geological Engineering, Recep Tayyip Erdo?an University, TR-53100 Rize, Turkey;2. Department of Geological Engineering, Gümü?hane University, TR-29000 Gümü?hane, Turkey;3. Department of Geological Engineering, Karadeniz Technical University, TR-61100 Trabzon, Turkey;4. Institute of Earth Sciences, University of Heidelberg, D-69120 Heidelberg, Germany;5. Department of Geological Engineering, Dokuz Eylul University, TR-35000 ?zmir, Turkey;1. Department of Geological Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey;2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;3. Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada;4. School of Earth Science and Mineral Resources, China University of Geosciences, 29 Xue-Yuan Road, Haidian District, Beijing 100083, China;5. Korea Basic Science Institute, YangCheong 804-1, Ochang, Cheongwon, Chungbuk 363-883, South Korea;6. Department of Geosciences, University of Adelaide, SA 5005, Australia |
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| Abstract: | Small granitoids emplaced into the early Jurassic volcani-clastic succession in the Yusufeli area, northeastern Turkey, can be temporally and geochemically classified into two groups: early Jurassic low-K and late Jurassic high-K. 40Ar–39Ar hornblende analyses yielded 188.0 ± 4.3 Ma for the Dutlup?nar intrusion, dating the subduction related rifting in the region. It comprises metaluminous to weakly peraluminous (ASI = 0.94–1.11) granodiorite and, to a lesser extent, tonalite whose K2O-poor (< 2.04 wt.%) nature and weak negative Eu anomalies (Eu/Eu? = 0.9–0.7) preclude derivation by fractional crystallization from a K-rich melt. Sr, Nd and Pb isotopic data reveal derivation by partial melting from an already cooled tholeiitic basic rocks which had mantle-like isotope signature. The Sumbated intrusion formed in the late Jurassic (153.0 ± 3.4 Ma) and consists chiefly of metaluminous (ASI = 0.84–0.99) quartz monzodiorite. Medium to high-K2O, relatively high MgO and Sr contents, flat HREE patterns without prominent Eu anomalies, slightly positive εNd(t) values (+ 1.5 to + 2.5) and low ISr ratios (0.7046–0.7056) are consistent with an origin by dehydration melting of a juvenile source, above the garnet stability field, dominated by likely K-amphibole bearing calc-alkaline mafic rocks. Geochemical data show that fractional crystallization from a Sumbated-like quartz monzodioritic magma is the fundamental process responsible for the evolved compositional range of the Keçikaya intrusion. The geochemical and geochronological data presented here indicate that the late Jurassic magmatism occurred in a post-collisional setting. Slab-breakoff, which was followed by shortly after collision, seems to be the most plausible mechanism for the generation of medium to high-K calc-alkaline rocks of the Sumbated and the Keçikaya intrusions, indicating a switch in the geodynamic setting, e.g., from pre-collision to post-collision in the middle Jurassic in the eastern Pontides. |
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