Geochronology, geochemistry, and petrogenesis of the Eocene Bayburt intrusions, Eastern Pontides, NE Turkey: Evidence for lithospheric mantle and lower crustal sources in the high-K calc-alkaline magmatism. (15th August 2015)

• Record Type: Journal Article
• Authors: Kaygusuz, Abdullah; Öztürk, Mürşit
• Is Part Of: Journal of Asian earth sciences. Volume 108(2015)
• Page Start: 97
• Page End: 116
• Publication Date: 2015-08-15
• Subjects: Eocene magmatism -- Sr–Nd–Pb–O isotope -- U–Pb zircon dating -- Eastern Pontides -- Turkey; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2015.04.017
• Languages: English
• ISSNs: 1367-9120

Abstract

Highlights: Eocene I-type plutons are widespread in the Eastern Pontides, NE Turkey. We report new geochemical, Sr–Nd–Pb–O isotopic and LA-ICP MS U–Pb zircon data. Studied intrusions are I-type, high-K calc-alkaline and metaluminous characters. The host rocks and their MMEs have similar geochemical and isotopic compositions. The pluton originated by mixing of lower crustal and mantle-derived end-members. Abstract: Eocene I-type plutons are widespread in the Eastern Pontides, Northeastern Turkey. Geochemical and isotopic results on two Eocene intrusive bodies located in the southern zone of the Eastern Pontides were utilized to achieve a proper reconstruction of their origin. Based on laser ablation ICP-MS U–Pb zircon dating, Kılıçkaya and Kozluk intrusions present similar 206 Pb/ 238 U versus 207 Pb / 235 U concordia ages of 46.75 ± 0.79 and 46.9 ± 0.68 Ma, respectively. Both intrusions exhibit similar petrographical, geochemical, and isotopical features, and contain abundant mafic microgranular enclaves (MMEs). The intrusive rocks are composed of diorite, tonalite, and granodiorite, whereas MMEs are composed of diorite. Both the intrusive rocks and the MMEs are I-type, high-K calc-alkaline in composition and display a metaluminous character. They are enriched in large-ion lithophile and light rare-earth elements and are depleted in high-field strength elements. The intrusive rocks show moderate variation in 87 Sr/ 86 Sr(i) (0.70531–0.70576), εNd(i) (+0.3 to −0.5), and δ 18 O values (+6.6 to +6.9), as well as Nd model ages (0.73–0.82 Ga). Their Pb isotopic ratios are 206 Pb/ 204 Pb = 18.67–18.86, 207 Pb/ 204 Pb = 15.61–15.62, and 208 Pb/ 204 Pb = 38.62–39.03. Although the isotope signatures of MMEs ( 87 Sr/ 86 Sr(i) = 0.70528–0.70561; εNd(i) = +0.7 to −0.3; δ 18 O = +6.7 to +6.8) are significantly similar to those of the host rocks, the MMEs are characterized by relatively low contents of SiO2 (57–59 wt.%), low aluminum saturation index (0.8–0.9), and high Mg numbers (31–36). All of these data suggest magma generation by mixing of enriched lithospheric mantle- and lower crustal-derived melts. Moreover, Sr–Nd isotopic modeling reveals ∼17% to 23% lower crustal magma contribution to the mantle component.