Zircon-apatite geochemistry and isotope constraints on VMS fertility in a late cretaceous back-arc basin, Eastern Sakarya Zone, Türkiye
CHEMICAL GEOLOGY, cilt.719, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 719
- Basım Tarihi: 2026
- Doi Numarası: 10.1016/j.chemgeo.2026.123562
- Dergi Adı: CHEMICAL GEOLOGY
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Compendex, Geobase
- Karadeniz Teknik Üniversitesi Adresli: Evet
Özet
Volcanogenic massive sulphide (VMS) deposits are common in submarine back-arc environments, yet mineralization is unevenly distributed even among volcanic successions formed within the same tectonomagmatic system. Here we investigate felsic volcanic sequences associated with the Murgul VMS district and stratigraphically equivalent barren successions from the Hatila Valley in the Eastern Sakarya Zone, northeastern T & uuml;rkiye, to evaluate how magma evolution and crustal magma transfer varied between fertile and barren domains within a single Late Cretaceous back-arc basin. Mafic rocks from both domains display comparable juvenile Nd-Hf isotope compositions, with epsilon Nd(t) = +1.3 to +3.7 and epsilon Hf(t) = +6.8 to +9.8 for Hatila rocks, and epsilon Nd(t) = +3.1 to +4.0 and epsilon Hf(t) = +8.6 to +10.0 for the Murgul VMS district, together with subductionmodified trace-element signatures, including elevated Th/Yb and Th/Nb ratios. These data indicate broadly similar mantle sources and slab contributions. In contrast, felsic rocks associated with VMS mineralization show restricted whole-rock epsilon Nd(t)-epsilon Hf(t) variability, with epsilon Nd(t) = +3.0 to +3.5 and epsilon Hf(t) = +8.3 to +9.2, limited intra-sample zircon epsilon Hf(t) dispersion, and coherent zircon trace-element arrays involving U, Th/U, and Nb/Ta versus Hf. Barren felsic suites show broader isotopic and geochemical dispersion, including whole-rock epsilon Nd(t) = -9.4 to +0.4, epsilon Hf(t) = -11.1 to +5.9, and zircon epsilon Hf(t) = -9.2 to +10.2. Zircon oxybarometry indicates broadly overlapping low- to moderately oxidized conditions in barren and fertile suites, with mean Delta FMQ values of +0.79 + 0.87 and + 0.31 + 0.34, respectively, suggesting that oxygen fugacity alone did not distinguish fertile from barren systems. Apatite compositions and Nd isotopes broadly parallel the zircon record, with Murgul apatite yielding epsilon Nd(t) = +1.6 to +3.6 compared with -1.0 to +2.2 in Hatila apatite. We interpret the fertile domain to reflect coherent juvenile felsic magma evolution, limited open-system crustal modification, and vertically connected magma transfer within a back-arc basin supplied by compositionally similar mafic magmas. These results highlight isotopic focusing, defined here as restricted isotopic dispersion expressed by limited whole-rock Nd-Hf variability and limited intra-sample zircon epsilon Hf(t) variation, together with accessory-mineralscale geochemical coherence, as indicators of magmatic conditions favorable for VMS development in submarine felsic volcanic successions.