Geochemical and Sr–Nd Isotopic Characteristics of Porphyritic Basalts from the Sincik Area, Southeastern Türkiye: Insights into the Genesis and Tectonic Setting of the Middle Eocene Maden Complex

Abstract

Porphyritic basalts exposed in the Sincik area of southeastern Türkiye form part of the Middle Eocene Maden Complex and provide an opportunity to characterise the geochemical and isotopic features of mafic magmatism along the Bitlis–Zagros Suture Zone. This study integrates petrographic observations, whole-rock major- and trace-element geochemistry, plagioclase mineral chemistry, and Sr–Nd isotopic compositions to evaluate the characteristics of the Sincik basalts. The studied rocks display porphyritic textures dominated by plagioclase, with subordinate pyroxene and amphibole. Whole-rock compositions are compositionally coherent and basaltic, with subparallel primitive mantle-normalised trace-element and chondrite-normalised rare-earth-element patterns. The samples are enriched in light rare-earth elements and display neutral to slightly positive Eu anomalies. Their trace-element characteristics indicate an enriched MORB- to OIB-like affinity, whereas positive εNd(T) values (+5.2 and +5.3) point to a significant depleted-mantle component. Relatively radiogenic initial Sr isotope ratios, together with AFC and EC-AFC modelling, indicate source enrichment accompanied by a limited contribution from crustal assimilation. Taken together, the geochemical and isotopic characteristics are consistent with derivation from an isotopically depleted but geochemically enriched mantle source, while non-modal batch melting modelling is broadly consistent with approximately 0.5–1.5% partial melting within the spinel-lherzolite stability field. The Sincik basalts represent a compositionally coherent alkaline basaltic phase within the broader geochemical diversity of the Maden Complex and provide new constraints on the nature and evolution of Middle Eocene mafic magmatism in southeastern Türkiye.