Pre-Himalayan tectono-metamorphic impresses in the Baijnath klippe, Kumaun Himalaya, NW India: Implications on a veiled saga of Paleoproterozoic−Neoproterozoic crustal evolution and thermal history of the northern Indian cratonic margin

Rocks of the Lesser Himalayan Sequence are important from a global tectonic perspective as they represent a crucial evolutionary chronicle of the Indian continent from the Paleoproterozoic to the Cenozoic Himalayan orogeny. Eroded remnants of tectonically transported crystalline thrust sheets overlying the Lesser Himalayan metasedimentary zone along the Main Central thrust are represented by the Almora, Baijnath, Askot, and Chiplakot klippen belts in the Kumaun Himalaya, India. In this work, we present the deformation history, geochemistry, and U-Pb zircon-apatite geochronology of the Baijnath klippe rocks and its footwall. Our age and tectonic setting results for the klippe rocks help to illustrate the continental accretion processes that prevailed during Paleoproterozoic−Neoproterozoic time along the northern Indian cratonic margin.

Granitoids within the Baijnath klippen yield crystallization ages varying from ca. 1870 Ma to ca. 1850 Ma, while the supracrustal sequence preserves a prominent age signature of ca. 1855 Ma. The metasediments of the Berinag Formation at the klippe footwall yield a detrital age of ca. 1810 Ma. Based on these results and the geochemistry, we infer that the Baijnath klippe rocks bear an affinity with the inner Lesser Himalayan Sequence, and the granitoid magmatism took place within a span of ∼20 m.y. (1870−1850 Ma) in an arc setting linked to active subduction along the north Indian continental margin, possibly due to the formation of the Columbia supercontinent during the Paleoproterozoic. Textural and mineralogical data from the amphibolite-facies supracrustals of the Baijnath klippe suggest that the progressive metamorphism (M₁) reached peak at ∼580 °C and ∼8.6 kbar followed by a decompression-dominated retrogression (M_1R) down to ∼450 °C and ∼5.8 kbar, possibly through a clockwise pressure-temperature (P-T) trajectory that was overprinted by the Cenozoic reworking (M₂ metamorphism?) and deformation (D₂) related to the Himalayan orogeny. Texturally constrained apatite grains from M₁ metamorphic domains preserve traces of a Neoproterozoic-age tectonothermal imprint that affected the Lesser Himalayan Sequence rocks, possibly during the assembly of the Gondwana supercontinent.