Petrography, geochemistry and regional significance of crystalline klippen in the Garhwal Lesser Himalaya, India

• Published in: Journal of Earth System Science 2011-06, Vol.120 (3), p.489-501
• Main Authors: ISLAM, R, GHOSH, S K, VYSHNAVI, S, SUNDRIYAL, Y P
• Format: Article
• Language: English
• Subjects: Calcium magnesium silicates; Chemical composition; Composition; Corundum; Crystallization; Deformation; Diopside; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; Fractional crystallization; Geochemistry; High temperature; Lithology; Mountains; Nucleotide sequence; Outliers (landforms); Oxides; Petrography; Petrology; Rocks; Similarity; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Strontium; Tectonics; Zirconium
• ISSN: 0253-4126; 2347-4327; 0973-774X
• DOI: 10.1007/s12040-011-0086-1

Uphalda gneisses (UG) is a crystalline klippe located near Srinagar in Garhwal Himalaya. These gneisses are compared with Debguru porphyroids (DP) (≈Ramgarh group) of Garhwal–Kumaun Himalaya and Baragaon mylonitic gneisses (BMG) of Himachal Himalaya. Petrographic study reveals that the deformation of UG was initiated at higher temperature (above 350°C) and continued till lowering of temperature and deformation led to the mylonitization. Geochemically, these granitic gneisses (UG, DP and BMG) exhibit similar composition. Features such as high molecular A/CNK value (>1), presence of normative corundum and absence of normative diopside, enhanced Rb/Sr, Rb/Zr ratios, enrichment of Th and containing rounded zircons support their crustally-derived S-type granitic nature. The linear plot in major oxides is interpreted in terms of fractional crystallization processes. Mantle normalized multi-element spider diagram of UG illustrates depletion of Ba, Nb, Sr, P and Ti and enrichment of Th and show similarities with DP and BMG. Similarities were observed in lithology, petrographic characters and chemical composition of UG, DP, BMG and Ulleri augen gneisses (Nepal). Comparison with the rocks of Higher Himalayan crystallines (≈Vaikrita), suggests that these rocks (UG) are not transported from Higher Himalaya as understood earlier. This study however proposes that, these gneissic bodies represent an older basement occurring as a tectonic sliver which emplaced within the cover sequence as wedges at different structural levels. This is a regional phenomena observed throughout the Lesser Himalayan region.