Geochronological and geochemical analyses of the rocks from the Baijnath Klippe, Kumaun Himalaya, North West India and its implications.
Abstract
The klippen belt in the Himalayan orogen, which includes the Almora, Bajnath, Askot and Chiplakot klippen, outcrop at the core of the orogen in the Kumaun-Garhwal region (Uttarakhand) of northwestern India. Valdiya (1980) opined that these synformal klippen rocks represent erosional remnants of the Palaeoproterozoic Lesser Himalayan Crystalline (LHC) nappe, thrust over the Lesser Himalayan Neoproterozoic-Eocene age sedimentary sequence. The largest of these klippen, the Almora klippe has been shown to consist of ca. 1.85 Ga mylonitized granite gneiss at the base overlain by a quartzite-schist sequence having 0.85 to 0.58 Ga youngest detrital zircon population, the whole being intruded by ca. 0.55 Ga granitoids (Trivedi etal., 1984; Mandal et al., 2015). Mandal et al. (2016) showed that the Askot klippe from the same belt consists of 1857 ± 19Ma granite-granodiorite gneiss at the base with overlying 1800 Ma Berinag quartzite. The Baijnath Klippe being an important member of this belt and situated north of the Almora Klippe, is unexplored till date as far as geochronology and geochemistry of the rocks are concerned. The present study is an attempt to ascertain the tectonostratigraphy of the Baijnath klippe from a combined approach of geochronology, geochemistry and structural studies of the klippe rocks. It has been observed that the klippe is mainly composed of granite gneiss, mylonites, augen gneiss and interlayered quartzite-metapelites of the Berinag Formation. Texturally and geochemically distinct two granitoid suites have been observed in the klippe. The one occurring along the Pindar riverbed, at the core of the klippe is intensely deformed and mylonitised while the other granitoid type occurring in association with the schists or metapelites and quatrzites along the flanks of the klippe, is in general less deformed. However restricted deformation and mylonitization is documented from such schist-granite boundaries, interpreted as a possible result of development of local thrust splays. Geochemically the riverbed granites and gneisses are of I-type character but the other body associated with the metasediments represents the S -type variety. The more evolved alkali-calcic I-type gneisses represents volcanic arcs of late- to post-collisional origin, which is in contrast to the calc-alkaline S-type granites signifying syn-collisional origin. Geochemically, the I-type and the S-type granites of the Baijnath klippe resembles the Ramgarh gneiss and the Almora gneiss of the Almora klippe (Das et al., 2019). However, U-Pb ages obtained from the geochemically distinct S-type and I-type granites of the Baijnath klippe indicate ca. 1823 ± 21 Ma age for all the samples. Detrital zircon data from the interlayered Berinag quartzite exhibits a well-defined peak around ca. 1860 Ma, with a minor peak around 2500 Ma and no grains younger than 1768 Ma (96% concordance). Thus the present data indicate that like the previously described Askot klippe and the Chiplakot klippe (Mondal et al., 2016; Das et al., 2019), the Baijnath Klippe is composed essentially of the Lesser Himalayan Crystalline rocks. This inference is at variance with the Almora klippe where the Lesser Himalayan Crystallines are overlain by the Neoproterozoic Higher Himalayan Sequence (HHS).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.T45C0243M