Zircon U–Pb geochronology and geochemistry of plagiogranites from Bela Ophiolite, Southern Pakistan: implications for the petrogenesis of oceanic plagiogranite

The Bela Ophiolite, located along the western margin of the Indian Plate in southern Pakistan, hosts a suite of intrusive plagiogranites (albitites, albite granites, and epidote granites) within its crustal section. In this study, we present zircon U–Pb geochronology, in situ Lu–Hf and Sr–Nd isotopes, and comprehensive geochemical analyses to constrain the origin and tectonic significance of these rocks. Zircon U–Pb geochronology yielded crystallization ages of ca. 65 Ma, with ε_Nd(t) values (3.9–6.9) and ε_Hf(t) values varying from 12.9 to 24.0, implying a genetic relationship with the depleted oceanic crust. Rare earth elements (REE) and multi-trace element patterns, as well as various trace-element covariations, confirm that the plagiogranites formed in response to partial melting. The low TiO₂ and Nb contents, slight LREE enrichment, and radiogenic (⁸⁷Sr/⁸⁶Sr)_i values of the Bela plagiogranites indicate that these rocks were likely derived from the partial melting of gabbros (oceanic layer 3) within a shear zone during the process of oceanic crust spreading. We interpret the Bela plagiogranites as products of forearc crustal anatexis during the initial subduction of Neo-Tethyan oceanic lithosphere between the Indian and Eurasian plates during the Late Cretaceous to Early Paleogene.