Geochemistry of Palaeoproterozoic Rocks of Aravalli Supergroup: Implications for Weathering History and Depositional Sequence

Abstract

The Paleoproterozoic Aravalli Supregroup of rocks, hosted in Aravalli Craton of NW shield, is deposited in shallow and deep water conditions. The major lithologies are phyllites and quartzites with significant components of greywacks and dolomite. Geochemical indices in particular, CIA (Chemical Index of Alteration) values (avg. phyllites: 51.6 -81.5, avg. quartzites: 57.4 -95.5) calculated from the data of clastic rocks of ASG suggest minimum to highly intense weathering in the source region. Other indices including PIA, CIW and ICV along with plot patterns on the A-CN-K diagram also nearly endorse CIA based interpretation. These rocks possess relatively high Th/U ratios compared to that found in fresh igneous rocks or their high grade metamorphic equivalents. This high Th/U ratio is neither a source inheritance nor a result of oxidation state rather a manifestation of Th hosting mineral accumulation through sorting. Viewed in the context of present stratigraphic succession, the weathering history adduced from geochemistry does not seem compatible but matches well with earlier classification scheme wherein the evolution of Aravalli Supergroup was considered episodic.

Geochemical Analysis of Cretaceous Shales from the Hazara Basin, Pakistan: Provenance Signatures and Paleo-Weathering Conditions

“…ICV values greater than one indicate immature shale, which includes rock-forming minerals such as plagioclase, K-feldspar, amphiboles, and pyroxene. The present study's average ICV results indicate the existence of K-feldspar (0.8-1) [43]. A cross plot of the CIA and ICV values reveals an interesting picture of the chemistry of the key elements.…”

Mineralogical and geochemical characteristics of the iron–duricrust deposit in Adi-Daero area, northwestern Tigray, Ethiopia: implication for the origin and controlling factors

“…An analogous compositional pattern was observed between Th and U in the profile (Table 2), in which their concentration smoothly decreases from the iron-rich duricrust downwards and shows positive correlation (clay-rich horizon: r = 0.83; iron-rich duricrust: r = 0.22; Table 3) between them. However, the significant increment of Th coupled with the decrement of U in the uppermost iron-rich duricrust (AD-1) implies that depletion of U was accompanied by mobilisation during weathering (Giorgis et al 2014; Singh and Khan 2017). Moreover, in an oxidising environment, relatively less soluble U 4+ transforms to more soluble U 6+ during chemical weathering, such that it is dissolved and lost from the system.…”

Sedimentological and petrochemical studies of Jurassic clastic rocks, Habo Dome Basin, Kachchh Mainland, Northwest India: Implications for depositional environment, provenance, and tectonic setting

“…Clastic sedimentary rocks are one of the main sources of information regarding past geological conditions that prevailed on the Earth's surface and exhumed ancient orogens (Absar & Srinivas, ; Fatima & Khan, ; P. K. Singh & Khan, ; Zimmermann & Bahulburg, ). Petrochemical studies including relative abundance of major framework components of sandstones, clay mineral abundance of shales and chemical composition of clastic rocks coupled with lithofacies records provide a better understanding of various sedimentological processes responsible for detritus generation to its final deposition (Condie, , ; Fatima & Khan, ).…”