Geochronology and geochemistry of the Panjal Traps from the southern Pir Panjal Range, Kashmir, India

The eruption of the Panjal Traps is associated with rifting along the Tethyan margin of Gondwana. A CA-ID-TIMS zircon U-Pb age of basalt collected from the southern Pir Panjal Range (SPPR) yielded a weighted-mean ²⁰⁶Pb/²³⁸U age of 288.2 ± 0.3 Ma. The rocks from the SPPR can be divided into three compositionally distinct groups (basalt: SiO₂ < 52 wt%; Mg# = 56–36, basaltic andesite: SiO₂ = 52–60 wt%; Mg# = 32–48, and silicic: SiO₂ > 64.0 wt%; Mg# = 27–23) and are chemically correlated with rocks from the eastern Kashmir Valley rather than the northern Pir Panjal Range (NPPR). The Sr-Nd isotopes (⁸⁷Sr/⁸⁶Sr_i = 0.70860–0.71104; ε_Nd(t) = −6.1 to −4.4) of the mafic rocks are similar and indicate that their magmas were derived from a subduction modified subcontinental lithospheric mantle (SCLM) source. The silicic rocks were derived by partial melting of the continental crust (⁸⁷Sr/⁸⁶Sr_i = 0.71022–0.71093; ε_Nd(t) = −8.7 to −7.2) and their discovery in the SPPR indicates that silicic volcanism was far more extensive than previously thought. The ¹⁸⁷Os/¹⁸⁸Os_i isotopic ratios of basalts from different regions of the Panjal Traps range from 0.1230 to 0.2832. Two samples from the NPPR have ratios of 0.1230 and 0.1256 that are slightly higher than primitive upper mantle at the time of eruption whereas the remaining samples show enriched values (0.1343–0.2832). The new data suggest that it is likely that the mantle source of the Panjal Traps transitioned from a SCLM source to a sublithospheric source over time as seafloor spreading developed.