Age and geochemistry of the Paleoproterozoic Bhatwari Gneiss of Garhwal Lesser Himalaya, NW India: implications for the pre-Himalayan magmatic history of the Lesser Himalayan basement rocks

Abstract

The Bhatwari Gneiss of Bhagirathi Valley in the Garhwal Himalaya is a Paleoproterozoic crystalline rock from the Inner Lesser Himalayan Sequence. On the basis of field and petrographic analyses, we have classified the Bhatwari Gneiss into two parts: the Lower Bhatwari Gneiss (LBG) and the Upper Bhatwari Gneiss (UBG). The geochemical signatures of these rocks suggest a monzonitic protolith for the LBG and a granitic protolith for the UBG. The UBG has a calc-alkaline S-type granitoid protolith, whereas the LBG has an alkaline I-type granitoid protolith; the UBG is more fractionated. The trace element concentrations suggest a volcanic arc setting for the LBG and a within-plate setting for the UBG. The U–Pb geochronology of one sample from the LBG gives an upper intercept age of 1988 ± 12 Ma (n = 10, MSWD = 2.5). One sample from the UBG gives an upper intercept age of 1895 ± 22 Ma (n = 15, MSWD = 0.82), whereas another sample does not give any upper intercept age, but indicates magmatism from c. 1940 to 1840 Ma. Based on these ages, we infer that the Bhatwari Gneiss has evolved due to arc magmatism and related back-arc rifting over a time period of c. 100 Ma during the Proterozoic. This arc magmatism is related to the formation of the Columbia supercontinent.Supplementary material: LA–ICP-MS calibration and adjusted major element data used for computing the isometric log-ratio transformations are available at https://doi.org/10.6084/m9.figshare.c.4272158

Zircons from Collisional Granites, Garhwal Himalaya, NW India: U–Th–Pb Age, Geochemistry and Protolith Constraints

“…80-60 Ma ago [9]. In the Paleoproterozoic era, many granites formed in the Himalayas from 1980 to 1750 Ma [12,[47][48][49] (Figure 11), and the 1.85 Ga Chail Group granites in the Garhwal Lesser Himalaya continue to be essential for any geological reconstructions. Evidence of old cores in zircons from granites varying in age from 3.5 to 2.1 Ga is analyzed to understand the genesis of the protolith.…”

Proterozoic felsic and mafic magmatism in India: Implications for crustal evolution through crust-mantle interactions

“…Malani Igneous Suite) with dominant volcanics mainly constitute the Aravalli-Delhi fold belts in NW India. Fort and Rai, 1999;Sharma and Rashid, 2000;Miller et al, 2000;Pandey, 2005;Singh et al, 2009;Rao and Sharma, 2009;Chakungal et al, 2010;Kohn et al, 2010;Rao and Sharma, 2011;Mandal et al, 2016;Ding and Zhang, 2016;Sen et al, 2018;Pathak and Kumar, 2019. The abbreviations and references used for various plots are the same as given in Figure 4.…”

Tectonics of the Western, Sikkim and Arunachal Himalaya

“…Based on field and petrographic analyses, Sen et al (2019) have classified the Paleoproterozoic Bhatwari Gneisses of the Garhwal Himalaya into the monzonitic Lower Bhatwari Gneiss (LBG) and the granitic Upper Bhatwari Gneiss (UBG). The UBG has a calc-alkaline S-type granitoid protolith, whereas the LBG has an alkaline I-type granitoid protolith; the UBG is more fractionated.…”