Magma nature and tectono-magmatic context of the Eocene Uludağ granitoids (NW-Türkiye): Insights into the Cenozoic geodynamics of the Tethyan Orogenic Belt

Abstract

<p>Late Paleocene to Middle-Eocene magmatism provides critical insights into the reconstruction of the Cenozoic geodynamic evolution of NW Anatolia. In this study, we mapped individual petrographic facies from the Eocene Uludag Plutons (Topuk and Tepeldag) and present zircon U-Pb geochronology, Sr-Nd isotope data, and comprehensive geochemical analyses for the entire plutons. We examined the Delice tonalite-granodiorite (D4) and Delice alkali-feldspar granite (D8) from the Topuk Pluton, as well as the Southern Tepeldag quartzmonzodiorite (ST1) from the Tepeldag Pluton. U-Pb zircon ages were 54.56 +/- 0.21 Ma for ST1, 47.35 +/- 0.21 Ma for D4, and 45.90 +/- 0.29 Ma for D8. Initial 87 Sr/ 86 Sr and 144 Nd/ 143 Nd values were calculated, showing 0.706693 and 0.512428 for ST1, 0.707309 and 0.512452 for D4, and 0.705896 and 0.512448 for D8, respectively. The new zircon U-Pb ages for these facies cover nearly the entire interval from 54 to 45 Ma, enabling a comparison of magma evolution with the Late Paleocene to Middle-Eocene (58-45 Ma) magmatism. Locally, patterns of magma replenishment, early-stage plagioclase accumulation, and later-stage dominance of amphibole fractional crystallization suggest a shift to fluid-related magma sources and sustained fluid release from the subducting Neotethys slab. Although changes in magma nature are common to both slab rollback and slab break-off, a comparative evaluation of Late Paleocene to Middle-Eocene granitoids supports continuous subduction and slab rollback for the Cenozoic geodynamic evolution of NW Anatolia. Continuous, systematic changes in magma character, a gradual decrease in Moho depth, and continuous tectonic shifts and evolution collectively indicate ongoing subduction and slab rollback dynamics rather than abrupt cessation. Our model for Western Anatolia proposes that early shallow subduction transformed into prolonged slab rollback in the west and early slab rollback transitioned to a more stable slab steepening regime in the east, shaping the tectonomagmatic evolution across the region.</p>