Miocene adakitic granites in central Pamir's Kuzigan region: Melting of thickened continental crust

This study focuses on the Cenozoic granites in the Kuzigan area of the central Pamir, integrating systematic petrogeochemical analyses and zircon U-Pb geochronology to elucidate the magmatic processes and their implications for lithospheric composition and deep-seated dynamics. LA-ICP-MS zircon U-Pb dating reveals that these granites were emplaced during the Miocene (14~11 Ma). Geochemically, the samples exhibit high silica (SiO2 = 71.04%~74.24%), potassium enrichment (K2O = 2.92%~5.81%), and low magnesium contents (MgO = 0.1%~0.56%; Mg# = 11.60~46.70), coupled with depleted Cr (2.26×10-6~21.20×10-6) and Ni (1.30×10-6~3.48×10-6). Notably, they display pronounced Sr enrichment (185.54×10-6~1 393×10-6) and significant Y (10.79×10-6~21.46×10-6) and Yb (0.82×10-6~1.86×10-6) depletion, with elevated Sr/Y (15.35~127.80) and (La/Yb)N ratios (21.83~346.59), consistent with typical high-Sr low-Y (HSRY) adakitic signatures. The low MgO, Mg#, and compatible element (Cr, Ni) concentrations, combined with high (Dy/Yb)N ratios (1.97~2.85) and CaO-Sr covariation trends, indicate the presence of garnet as a residual phase in the magma source, supporting a genesis through partial melting of thickened lower crust (> 50 km). In the context of ongoing India-Eurasia collision, the Miocene (13.5~10.9 Ma) magmatism in the central Pamir is interpreted as a response to localized lithospheric destabilization. Gravitational collapse of thickened crust triggered asthenospheric upwelling, facilitating partial melting of ancient lower crustal materials and generating adakitic granites with HSRY affinities. These findings provide critical insights into the crustal evolution of the Pamir orogen and the mechanisms of post-collisional magmatism.