Water–rock interaction on the development of granite gneissic weathered profiles in Garhwal Lesser Himalaya, India

Abstract

The development and sustainability of weathered profiles are very difficult in the Himalaya due to its complex lithology, tectonic history and fast erosion. Despite this, two weathered profiles namely WPa (weathered profile a) and WPb (weathered profile b) which have sustained erosion are developed on porphyry granite gneiss and granite gneissic lithology in Alaknanda valley of the Garhwal Lesser Himalaya. Systematic sampling of these two weathered profiles was done from bottom to top and they were chemically analysed to understand the elemental mobility in each profile. Major, trace and rare earth element studies show dissimilar behaviour with the advancement of weathering. In WPa profile, the CIA value of LAR (LAR) is 50 which reveals that the rock has not suffered any alteration but in WPb profile, the CIA value of LAR is 64 which indicates significant amount of chemical alteration. A-CN-K projection also exhibits similar behaviour. Further, the relative mobility of all the major and trace elements show variable elemental distribution in both the profiles. Enrichment of Mg, Fe, Ti, Al, Co, Ni, Zr, LREE and depletion of Na, K, P, Ca, Si, LILE and HFSE are observed in WPa profile; while the depletion of Na, K, Ca, P, Si, HREE and enhancement of Fe, Mn, Ti, Sc, Co, Zr, LREE are noticed in WPb profile. The rare earth elements also show a dissimilar mobilization pattern in both the profiles due to their strong dependency on lithology, and corresponding climate and tectonic interaction. Contrasting elemental mobility in both the profiles depict the major role in disparity of lithological characters and subsequent development of fractures produced by the major thrust system (Ramgarh thrust) which made an easy passage for rain water, thus causing the development of a chemically altered profile in the Lesser Himalayan region. Further, the present study infers the climate and tectonic milieu which is responsible for the development of such weathered profiles in Himalayan sector.

Investigations on baseline levels for natural radioactivity in soils, rocks, and lakes of Larsemann Hills in East Antarctica

“…Uranium concentrations observed in the lake water and ice samples from the present study are within the range reported for lakes near McMurdo Dry Valleys (Henderson et al, 2006). The sources of U in the lake water in the study area are mainly from deposition of the sea-salt aerosols and rock/soil-water interactions (Röthlisberger, 2002;Vyshnavi & Islam, 2015). The mean tritium concentration in the lakes of Larsemann Region is around 1.3 Bq/L which is much less than observed by Pourchet et al (1997) as shown in Table 6.…”

Recent Contributions in the Field of Sediment Geochemistry

“…Papers on rock weathering in the Himalayan region were contributed by Vyshnavi and Islam (2015) and Vyshnavi et al (2013). Vyshnavi and Islam (2015) studied two weathered profiles developed on porphyry granite gneiss and granite gneiss in the Alaknanda valley of the Garhwal Lesser Himalaya.…”

“…Vyshnavi and Islam (2015) studied two weathered profiles developed on porphyry granite gneiss and granite gneiss in the Alaknanda valley of the Garhwal Lesser Himalaya. By the use of major, trace and rare earth elements the study found that the climate and tectonic milieu was responsible for the development of such weathered profiles in the Himalayan sector.…”

“…Despite a complex sequence of processes modify the sediment geochemistry, in situ weathering, sediment sorting, and mixing processes are the major defining factors of the sediment's geochemistry. Chemical weathering of rocks fractionates weatherable minerals from resistant minerals (see Vyshnavi et al, 2013;Vyshnavi and Islam, 2015;Gaur et al and Patel et al, 2014). Hydraulic activity during transport fractionates the coarse-grained particles from the fine-grained weathered products (see Khanna et al, 2011;Shynu et al, 2011;Rao et al, 2015).…”

Regolith Profiles Developed from a Granitic Parent Rock in a Sub-Humid Region of India: Implications for Pedogenesis and Chemical Mobility of Elements

“…Rocks exposed to abundant rainfall and hot temperatures in tropical regions weather much faster than similar rocks residing in cold and dry regions (Hunt et al, 2021). Low relief of the area results in more water percolation enhancing weathering that is responsible for the destruction/alteration of unstable minerals in regoliths (Fedo et al, 1995;Vyshnavi and Islam, 2015).…”