TITLE:
Geochemistry of Palaeoproterozoic Rocks of Aravalli Supergroup: Implications for Weathering History and Depositional Sequence
AUTHORS:
Pavanesh K. Singh, M. Shamim Khan
KEYWORDS:
Clastic Geochemistry, Aravalli Supergroup, Rajasthan, Palaeoweathering, Indian Shield
JOURNAL NAME:
International Journal of Geosciences,
Vol.8 No.10,
October
31,
2017
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.