Melting of the juvenile lower crust in a far-field response to roll-back of the southern Neotethyan oceanic lithosphere: the Oligocene adakitic dacites, NE Turkey

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dc.authoridKarsli, Orhan/0000-0002-2904-6227
dc.contributor.authorKarsli, Orhan
dc.contributor.authorCaran, Semsettin
dc.contributor.authorCoban, Hakan
dc.contributor.authorSengun, Firat
dc.contributor.authorTekkanat, Osman
dc.contributor.authorAndersen, Tom
dc.date.accessioned2025-01-27T20:14:27Z
dc.date.available2025-01-27T20:14:27Z
dc.date.issued2020
dc.departmentÇanakkale Onsekiz Mart Üniversitesi
dc.description.abstractLate Cenozoic tectono-thermal events and associated magmatism in the Sakarya Zone (SZ) are still contested. Although documented in the western part of the SZ, thus far, no magmatic activity has been identified in the eastern part of the Oligocene SZ. Here, we report a newly identified Oligocene magmatism to interpret the genesis with tectonic setting and gain new insight into the geological evolution of the eastern SZ. We present extensive geochemical, bulk-rock Sr-Nd and zircon Hf isotope, and zircon U-Pb chronological analyses for the Tepebasi dacites in the Artvin area, NE Turkey. Zircon UPb dating analyses revealed a dacite formation age of similar to 29.8 +/- 0.3 Ma. Geochemically, with a K2O/Na2O ratio of 0.5 to 0.6, they are composed of rocks of a medium-K calc-alkaline adakitic affinity. The samples are further characterized by low Y (6-7 ppm), and high Sr (362-588 ppm) and Sr/Y ratios (58-98), with low Mg# (41-45) values, demonstrating a close affinity with the crustal source of adakitic rocks. They have slightly radiogenic isotope concentrations (Sr-87/Sr-86(t) = 0.70460-0.70544, epsilon(Nd)(t) = +1.7 to +2.0), and single-stage Nd model ages of T-DM1 = 0.61-0.63 Ga, as well as uniform and positive epsilon(Hf) (t) of 8.2-10.5, with young Hf depleted mantle ages (T-DM1 = 0.31-0.41 Ga). These isotopic features, in combination with the geochemical signature, preclude a mantle origin. Instead, they most likely originated from a juvenile mafic lower crustal material by low degree partial melting (<%5) rather than through partial fusion of a subducting slab or thickened lower crust. Trace element modeling reveals that the mafic juvenile lower crust is composed of <10% garnet-bearing amphibolite. Furthermore, trace element compositions imply that adakitic melts formed in an extensional setting without delamination of a thick mafic lower continental crust. We conclude that the Oligocene adakitic magmatism originated in an intracontinental setting, which was subjected to far-field extensional forces induced by roll-back of south Neotethyan oceanic lithosphere just before its detachment in the collision zone. We believe that hot asthenospheric upwelling due to the far-field extension induced by the roll-back of the southern branch of the Neotethyan oceanic lithosphere triggered adakitic magmatism. The heat induced by the upwelling of the asthenosphere likely led to the heat-fluxed melting of juvenile mafic crustal material in such an extensional tectonic setting during the Oligocene epoch in the eastern SZ. (C) 2020 Elsevier B.V. All rights reserved.
dc.description.sponsorshipSuleyman Demirel University [SDUBAPKB 2205-YL-10]; Hefei University of Technology, China
dc.description.sponsorshipThis work was financialy supported by Suleyman Demirel University, with a project (grant#SDUBAPKB 2205-YL-10). We appreciate Dr. Bin Chen from the Hefei University of Technology, China, for the Sr\\Nd radiogenic isotope analyses and thank to Mehdi Ilhan and Emrah Yildiz for their assistance during the zircon preparations. Raif Kandemir is acknowledged for his efforts on the figure designing. This contribution significantly benefited from the reviews by Prof. Dr. Durmus Boztug and one anonymous reviewer as well as the comments from Co-Editor-in-Chief Prof. Dr. Michael Roden.
dc.identifier.doi10.1016/j.lithos.2020.105614
dc.identifier.issn0024-4937
dc.identifier.issn1872-6143
dc.identifier.scopus2-s2.0-85086712513
dc.identifier.scopusqualityQ1
dc.identifier.urihttps://doi.org/10.1016/j.lithos.2020.105614
dc.identifier.urihttps://hdl.handle.net/20.500.12428/21098
dc.identifier.volume370
dc.identifier.wosWOS:000558896300009
dc.identifier.wosqualityQ1
dc.indekslendigikaynakWeb of Science
dc.indekslendigikaynakScopus
dc.language.isoen
dc.publisherElsevier
dc.relation.ispartofLithos
dc.relation.publicationcategoryinfo:eu-repo/semantics/openAccess
dc.rightsinfo:eu-repo/semantics/closedAccess
dc.snmzKA_WoS_20250125
dc.subjectFar-field extension
dc.subjectPartial melting
dc.subjectJuvenile mafic crust
dc.subjectAdakitic magmatism
dc.subjectSakarya Zone
dc.subjectNE Turkey
dc.titleMelting of the juvenile lower crust in a far-field response to roll-back of the southern Neotethyan oceanic lithosphere: the Oligocene adakitic dacites, NE Turkey
dc.typeArticle

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