Age and Petrogenesis of the Paleogene Rapakivi-Textured Granites from the Central Pamir, Tajikistan

Rapakivi granites are commonly interpreted as products of interaction between mantle-derived and crustal magmas, yet their origin in collisional orogens remains poorly understood. Here we investigate the petrogenesis and tectonic significance of the middle Eocene Jamak pluton in the Central Pamir using zircon U–Pb geochronology, zircon trace-element geochemistry, mineral chemistry, and whole-rock geochemical data. Zircon U–Pb dating yields a crystallization age of 40.20 ± 0.24 Ma, confirming emplacement during a regional pulse of Eocene magmatism associated with the early stages of the India–Asia collision. The granites display characteristic rapakivi textures and high-K calc-alkaline, metaluminous to weakly peraluminous compositions. Trace-element patterns are marked by enrichment in large-ion lithophile elements, depletion in high-field-strength elements, high Sr/Y and La/Yb ratios, and adakitic affinities, indicating a significant lower-crustal contribution. Zircon trace-element compositions, Ti-in-zircon thermometry, and oxygen fugacity estimates reveal episodic thermal perturbations, magma replenishment, and the involvement of high-temperature mantle-derived melts. Distinct rare-earth-element patterns recorded by zircon cores and rims, together with the bimodal character of the pluton and widespread rapakivi textures, indicate interaction between two compositionally contrasting magmas. While bearing I-type-like geochemical affinity, they show signatures of post-collisional magmatism. We interpret the granites as products of mixing between asthenosphere-derived mafic melts and felsic melts generated by partial melting of garnet-bearing lower crust, from which they inherited the I-type geochemical signatures. The geochemical characteristics of the Jamak pluton are most consistent with localized convective removal of lithospheric mantle beneath the Central Pamir, which promoted asthenospheric upwelling, mafic underplating, lower-crustal melting, and magma hybridization.