The geochemistry of Mesoproterozoic clastic sedimentary rocks from the Rautgara Formation, Kumaun Lesser Himalaya : Implications for provenance, mineralogical control and weathering

The Mesoproterozoic clastic sedimentary rocks, comprising pelites and quartzites from the Rautgara Formation, Kumaun Lesser Himalaya, have been analysed for major and trace elements, including Rare Earth Elements (REEs) to evaluate their provenance and weathering history. The pelitic rocks are characterized by moderate SiO 2 and Al 2 O 3 contents and show consistent REE patterns with LREE (light REE)-enriched and HREE (heavy REE)-depleted patterns (La N /Yb N = 7.4-10.3). The total REE abundances of Rautgara pelites are high (up to 266 ppm) with large negative Eu-anomalies (Eu/ Eu* = 0.57-0.64). Except high SiO 2 contents, the other major and trace element concentrations are significantly low in the associated quartzites. Although the quartzites contain low REE abundances (up to 41 ppm), their patterns, including negative Eu anomalies, are akin to pelites, suggesting that both the rock types be derived from similar source. The Chemical Index of Alteration and A-CN-K parameters indicate that moderate chemical weathering has taken place in the source region of the Rautgara rocks. The linear correlation coefficients between Al 2 O 3 , K 2 O, TiO 2 and total REE reveal that the accessory minerals (mainly Ti-bearing phases) have hosted the REEs. The striking similarities between the REE patterns of Rautgara pelites and BGC of Aravalli and Bundelkhand granitoids, which are consistent with the palaeocurrent studies of the area, indicate that the granitoid rocks from these regions have supplied detritus to the Lesser Himalayan Rautgara sedimentary basin.