Precambrian Rocks from Lesser Garhwal Himalaya and Its Possible Linkage with Northern Indian Peninsular Shield

Understanding the early (older than 2.5 Ga) earth evolution and its geodynamics is one of most fundamental scientific issues in geology. The evolutionary trends of the every segment of planet earth are important with adequate knowledge of this period. Therefore, we select the granitic rocks from lesser Garhwal Himalaya of Proterozoic component and collected about 33 samples of felsic rocks, less studies from Garhwal Himalaya and compare their petrogenesis, geochemistry and Sm-Nd isotope analysis with Bundelkhand craton (northern Indian peninsular shield). . The lesser Himalayan Proterozoic granitic samples are classified as peraluminous with low Na₂O and high K₂O content in the Garhwal region. These granites of Proterozoic ages are characterized by K-rich (K₂O/Na₂O=1.25-9.33) which may be inferred to be formed by delaminated lower continental crust or partial melting of a thickened crust. The avg. Al₂O₃ (12.68 wt.%) in the granites is greater than the avg. total alkalis (7.47 wt.%) with TiO₂ 0.06-0.39. In tectonic discrimination diagram, magnesian rich granites falls in syn-collision tectonic settings (Pearce et al. 1984). With negative Eu (Eu/Eu* =0.11-0.4) anomalies in granites are characterized by variable negative Nb, Ba, Ti and Sr anomalies suggest the contribution of continental crust composition in the source of magma. We analysed Sm-Nd isotopes of three samples of granites from Lesser Garhwal Himalaya and calculated modal ages at c.a. 1.8 Ga, isotopic model ages are extended to 2.89 Ga, which suggest the recycling of older crust of Mesoarchean sources. The geophysical studies of Bundelkhand craton mostly consists of Archean granitic rocks indicative of a northward dipping tectonic fabric of this region which confirms to the subduction towards Himalaya (Gokarn et al. 2013). Therefore, we assume that the c.a. 2.1-1.8 Ga felsic magmatism in the lower part of the Himalaya, believe the involvement of Mesoarchean crust from southern side possibly of Bundelkhand craton of adjoining part.