MULTIPLE MANTLE SOURCES OF THE PANJAL TRAPS RELATED TO THE CONTINENTAL RIFT-OCEAN BASIN TRANSITION

The Panjal Traps of northern India are the volcanic remnants of continental rifting which led to the Early Permian formation of the Neotethys Ocean and the development of the ribbon-like continent Cimmeria. Samples collected from the eastern side of the Kashmir Valley are chemically similar to mildly alkaline to tholeiitic, within-plate flood basalts. The low TiO₂ contents (i.e. TiO₂ = 0.6 to 3.2 wt%), La/Yb_N values (i.e. La/Yb_N = 1.8 to 6.0) and εNd_(T) values (i.e. εNd_(T) = -5 to +1.3) along with partial melt modeling indicates that the basalts were derived from a spinel peridotite source that was enriched (i.e. EMII). In contrast, samples collected from the western side of the Kashmir Valley are more primitive in composition and show evidence for clinopyroxene fractionation. Although their TiO₂ (i.e. TiO₂ = 0.7 to 1.5 wt%) compositions and La/Yb_N values (i.e. La/Yb_N = 0.9 to 5.1) are similar to the eastern side, the western samples have much higher Mg# (Mg# = 50 to 77) values and εNd_(T) values (i.e. εNd_(T) = -0.1 to +4.5) suggesting they were derived by slightly higher amount of partial melting and from a more depleted spinel peridotite source. The changing bulk composition of the basalts from more enriched OIB-like on the eastern side to more depleted MORB-like compositions on the western side is likely due to the changing nature of the Panjal rift from a nascent continental setting to one that is transiting to a mature ocean basin. The precise reason for the initial rifting along the northern margin of southern Gondwana is unclear however it may be related to the exploitation of ‘structural heterogeneities’ within the crust which developed as a consequence of de-glaciation of the Late Paleozoic ice sheet.