Petrogenesis and geochemistry of camptonites and lamprophyres from Central Sakarya, NW Anatolia, Turkey: insights into post-orogenic magmatism and slab rollback

We present petrographic, mineral chemical, whole-rock geochemical, and Sr–Nd–Pb isotopic data for mid-Miocene camptonites and lamprophyres from Central Sakarya, Turkey, to constrain mantle sources and post-orogenic evolution in northwestern Anatolia. Sample MgO contents ranged from 1.3 to 6.7 wt.%. The rocks are porphyritic to locally panidiomorphic and comprise amphibole, clinopyroxene, feldspar, Fe–Ti oxides, and sulphides. Feldspar occurs as prominent phenocrysts in camptonitic samples but mainly as smaller grains or groundmass phases in lamprophyres. Whole-rock data indicate calc-alkaline to high-K calc-alkaline affinities, enriched lithospheric-mantle signatures, positive Pb anomalies, low Ce/Pb values, negative Nb–Ta anomalies, LREE enrichment, and minor negative Eu anomalies. Isotopic compositions are enriched relative to depleted mantle, with 87Sr/86Sr = 0.704785–0.706194, εNd = -0.3 to +2.8, and 206Pb/204Pb = 18.64–18.78. The lack of systematic correlations between radiogenic isotope ratios and differentiation indices indicates that shallow crustal assimilation was not the primary control. Instead, the data support partial melting of a metasomatized lithospheric mantle source influenced by sediment- and/or continent-derived components, with limited crustal interaction during ascent. These data provide local constraints on volatile-rich mafic magmatism and support models linking Miocene extension and slab rollback to mantle melting along the İzmir–Ankara–Erzincan Suture Zone.