Magmatic fertility in post-collisional arcs: contrasting juvenile mafic intrusions and Cu-Mo fertile felsic systems in the Eastern Sakarya Zone (NE Türkiye)

Abstract

The Eastern Sakarya Zone (ESZ) of northeastern T & uuml;rkiye records a remarkable duality in Eocene magmatism, where Cu-Mo fertile felsic porphyries coexist with barren mafic-intermediate intrusions. We present an integrated, multi-proxy investigation of the I(center dot)spir intrusive complex, incorporating whole-rock geochemistry, zircon U-Pb-Hf isotope-trace element systematics, and apatite major-trace element and in-situ Nd isotopic signatures, to delineate the petrogenetic pathways and magmatic processes that control fertility contrasts across this intrusive suite. Zircon and apatite proxies reveal that I(center dot)spir magmas were derived from a juvenile mantle source, retained consistently radiogenic isotopic signatures, and crystallized under relatively reduced, volatile-poor conditions. In contrast, fertile Eocene felsic intrusions in the ESZ show enriched isotopic signatures, elevated oxidation states, and volatile-rich magmas derived from a metasomatized mantle source and buffered in longlived crustal magma reservoirs, conditions favorable for porphyry Cu-Mo fertility. Apatite-derived estimates of Cl, F, S, and Delta FMQ further distinguish these suites, with fertile magmas showing elevated halogens and sulphur contents coupled with oxidized states favorable for delayed sulphide saturation and metal transport. These results demonstrate that in post-collisional arcs, fertility depends not only on tectonic triggers such as slab break-off or lithospheric delamination but also on whether melts are processed through volatile-charged, oxidized hot zones. The I(center dot)spir suite provides a critical juvenile end-member against which fertile felsic counterparts can be contrasted, offering a refined framework to assess magmatic fertility across the Tethyan Metallogenic Belt and other collisional orogens.