Provenance and sedimentation age of the Proterozoic clastic succession of the Garhwal‐Kumaon Lesser Himalaya, NW‐India: Clues from U–Pb zircon and Sr–Nd isotopes

Abstract

The paper presents data on the U-Pb chronology of detrital zircon grains and radiogenic isotopic composition ( 87 Sr/ 86 Sr, ϵNd) from the Proterozoic clastic successions of the Garhwal-Kumaon Lesser Himalaya representing the extended northern Indian cratonic margin, NW India. The Proterozoic Lesser Himalayan Basin in Garhwal-Kumaon Himalaya is divided into two sectors, namely, Inner Lesser Himalaya (ILH) and Outer Lesser Himalaya (OLH) by a tectonic boundary, namely the Tons Thrust (TT). Age distribution from inner and outer sectors of the Lesser Himalaya shows that the U-Pb chronology of most of these zircons provides Palaeoproterozoic (between 1.6 and 1.8 Ga) to Neoproterozoic (800 Ma) ages. The age data suggest sedimentation of the Rautgara Formation (Damtha Group) of ILH continued till the Neoproterozoic ($850 Ma), which was earlier regarded as ≤1.6 Ga. Tracking the detrital U-Pb zircon ages in the near adjacent cratonic parts point towards Aravalli Orogen as the major source region. Wholerock Ɛ Nd(0) values for ILH rocks range from À37.6 to À14.6 and for OLH it ranges from À19.6 to À6.7. More negative Ɛ Nd values along with dominance of Neoarchean-Palaeoproterozoic ages in ILH indicates supply from more evolved protolith or recycled sources and less negative Ɛ Nd values with major Neoproterozic zircon ages from OLH supports for less evolved source rock. The change from more negative Ɛ Nd to less negative Ɛ Nd values progressively upward the stratigraphy can be due to a shift in source with time. Both U-Pb zircon and Ɛ Nd supports for a continuous sedimentation model, rule out the presence of $500 Ma unconformity within the LH and argues for separate evolution of the Lesser Himalayan Basin on the trailing edge of the extended north Indian craton in "Columbia" configuration.

Oceanic Redox State During the Early Cambrian: Insights From Mo‐S Isotopes and Geochemistry of Himalayan Shales

“…Fine laminations with disseminated pyrite grains (mm sized) were observed in hand specimens of the shales. For geochemical comparison, a few shale samples from an underlying (Jaunsar) Group of Neoproterozoic age (Negi et al., 2022; Richards et al., 2005) were also collected from a road‐cut section (30°30′50.40″N, 77°59′49.20″E). The collected samples from both sections were powdered and homogenized (to <100 μm size) using an agate mortar and pestle.…”