ABSTRACT U–Pb isotope and trace element geochemistry of apatite combined with whole‐rock geochemistry from four carbonatite bodies (Sillai Patti “SP”, Loe Shilman “LS”, Warsak “WC”, and Jambil “JC”) in the Peshawar Plain Alkaline Igneous Province (PPAIP), western Himalaya were used to elucidate petrogenetic source, magma evolution, emplacement timing, and post‐magmatic hydrothermal/metasomatism of carbonatites. Whole‐rock geochemistry classifies the studied bodies as calcio‐carbonatites, except WC, which shows a transition from calcio‐ to ferruginous variety. Major/trace element geochemistry suggests primary magmatic records in SP and LS samples, localized fluid‐assisted chemical modifications in WC samples, and intense metasomatism in JC samples. Three types of apatites were identified in the four carbonatite bodies. Well‐developed, euhedral, concentric zoned apatite grains, exhibited by CL‐dark homogeneous cores in SP, LS, and WC, are termed as Group I. Apatite grains with irregular or spongy‐type internal structures, spotted CL‐bright patches or overgrowths in LS, SP, and WC are classified as Group II. Whereas structurally and geochemically distinct, possessing murky textures and unclear growth domains in JC were classified as Group III. The U–Pb isotope ratios from the CL‐dark inner and homogeneous domains of Group I apatite in WC and SP carbonatites yielded concordia ages of 280 and 268 Ma, respectively, indicating primary magmatic stage of the carbonatite emplacement, whereas 199 Ma is from apatite from LS samples. The CL‐bright outer domains of Group II apatite in LS, SP, and WC showed ages of 101, 96, and 91 Ma, respectively, suggesting overgrowth or recrystallization due to an additional pulse of magmatism. Group III apatite in JC gave U–Pb age values of 29 Ma, showing a complete overprint on the earlier magmatic records. Trace and rare‐earth element data in Group I apatite reveal carbonated mantle‐derived melts, slightly depleted REE values with some chemical modification in Group II apatite linked with recrystallization or overgrowth, and highly depleted REE and chemically distinct Group III apatite indicating fluid‐mediated metasomatism. Apatite textural features, trace‐element geochemistry, and geochronological records indicate differing magma fertility and REE enrichment that was potentially linked with progressive magmatic evolution and late‐stage fluid activity. The newly obtained U–Pb isotope and geochemical data from apatite and geochemical signatures in whole rock provide strong evidence elucidating the protolith information of PPAIP carbonatites and late‐stage metasomatism.
Rashid et al. (Sun,) studied this question.