Geochemistry of the Archaean metasedimentary rocks of the Bundelkhand Mauranipur-Babina greenstone belt, central India: Implications for provenance characteristics

Abstract

Abstract

Metasedimentary rocks occurring as minor components of Mauranipur- Babina greenstone belt of the Bundelkhand craton were analyzed for major oxides and trace elements to constrain the composition and weathering history of their provenance and the tectonic setting prevailing at the time of deposition. On the basis of mineralogy and geochemical compositions, two types of lithologies are identified. First, a texturally immature, medium to coarse grained, light-coloured rock distinguished as Arkose. Second, a fine grained, dark coloured metapelitic rock containing adequate amount of mafic minerals, identified as greywacke. CIA (chemical index of alteration) and CIW (chemical index of weathering) values and Th/U ratios suggest that the source area of these sedimentary rocks had only been weekly weathered. ICV (Index of compositional variability) values of these rocks are <<1, suggesting that the sediments are generally immature. Low degree of weathering in their source region, immature nature and minor sorting influence on the detritus are the features which suggest high rate of erosion, rapid sedimentation, potentially marked relief and short distance transportation of the debris, derived from a tectonically active source region. Th- Sc- Zr systematic suggests insignificant degree of recycling. Assessment of provenance composition using Al₂O₃ - TiO₂, Sc-Th/Sc and (CaO+MgO) - SiO₂ – (Na₂O₊ K₂O_), variation diagrams, REE patterns and (La/Yb)n ratios suggest that the studied sedimentary rocks were derived from mixing of debris of felsic and mafic composition in different proportions. The provenance modelling using REE data indicates that the arkoses can be best modelled with an 80% TTG and 20% granite mixture. On the other hand the greywacke can be best modelled with a mixture having 50% TTG, 40% basaltic rocks and 10% granite.  It is suggested that the basin experienced contemporaneous sedimentation of immature detritus derived from a young craton comprising TTG and granitic batholiths and syn-depositional volcanic centres in an active tectonic environment.