Zircon U-Pb dating, whole-rock and Sr-Nd isotope geochemistry of the Reshian granite gneiss of Indian Shield in Jhelum Valley, Lesser Himalayas (Azad Kashmir, Pakistan)

摘要

The Reshian area lies in the Lesser Himalayas (LH) in Jhelum valley, Azad Kashmir. The present study is carried out to investigate detailed petrological, geochemical, and geochronological characterization of granitic gneiss. Petrological investigation exhibits that the protoliths of Rashian granitic gneiss (RGG) are syenogranite to monzogranite. Geochronological study infers the protoliths formed in the Neoproterozoic (823 +/- 14 Ma and 843 +/- 12 Ma), representing the crystallization age of early granitic magma. Petrographical and geochemical study suggests the characteristics of the RGG are S-type, less Si, rich K, depletion in rare earth element (REE), the enrichment of light rare earth element (LREE), negative Eu anomaly, alkali to alkali-calcic, and peraluminous to slightly metaluminous granite. Meanwhile, the study implies the source of the RGG was derived mainly from partial melting of greywacke. Moreover, they have initial Sr-87/Sr-86 ratios ranging from 0.705823 to 0.714078, and initial epsilon Nd values varying from - 34.3079 to - 15.1398, revealing that the magma of the RGG was sourced from the fractional melting of the crustal material. Additionally, the RGG was emplaced in the post-collisional setting with the nature of syn-collisional granites and volcanic arc granites, implied probably due to the thermal perturbation associated with the breakup of the Rodinian supercontinent.