Redefining the tectonostratigraphic and structural architecture of the Almora klippe and the Ramgarh–Munsiari thrust sheet in NW India

Abstract

AbstractWe integrate U–Pb zircon geochronology and εNd(0) values with field mapping to determine which tectonostratigraphic units are represented to the north, south and within the Almora klippe in Kumaun, NW India. Rock in the Almora klippe and north of the Main Central thrust (MCT) have Neoproterozoic (c. 900 Ma) detrital zircon ages, coupled with similar εNd(0) (−7.6 to −11.8) values, suggesting that these two units are the same tectonostratigraphic unit, and that the Almora klippe is the southern continuation of the MCT or another thrust in the Greater Himalayan thrust system. However, north of the Almora klippe, detrital zircon age populations establish the presence of Palaeoproterozoic rock instead of the previous interpretation of Neoproterozoic rocks. These Palaeoproterozoic Lesser Himalayan (LH) rocks are carried by the Ramgarh–Munsiari thrust (RMT) dipping south and folded underneath the klippe. South of the klippe, the RMT carries both the less metamorphosed Palaeoproterozoic and Neoproterozoic LH rocks, in disagreement with the idea that only Neoproterozoic–Cambrian LH rocks are present south of Almora klippe. These results suggest that previous cross-sections in Kumaun are incorrect and must be re-evaluated.Supplementary material:U–Pb zircon geochronological data table is available at http://www.geolsoc.org.uk/SUP18777.