Geochemistry of clastic sediments from Sargur supracrustals and Bababudan group,Karnataka: Implications on Archaean Proterozoic Boundary |
| |
Authors: | S K Bhushan Priyadarshi Sahoo |
| |
Institution: | (1) Dept. Geology, University of Rajasthan, 302004 Jaipur, India |
| |
Abstract: | The sediments from three stratigraphic levels in the Bababudan schist belt of Dharwar craton exhibit great diversity in major,
trace and rare earth element (REE) geochemistry and thus interpreted to represent significant compositional variation in the
source rocks. Detailed geological and geochemical studies have been carried out on clastic rocks constituting the Archaean
Sargur supracrustals and the Bababudan belt of Dharwar craton (DC), southern India for understanding the geochemical characteristics
and to define the Archaean-Proterozoic Boundary (APB/QPC) in southern India. There is significant contrast in the geochemical
signatures for the sediments from these stratigraphic levles. The Sargur enclave population is characterised by slight LREE
enrichment with (La/Sm)N ranging from 1.45 to 3.58, almost flat HREE with (Gd/Yb)N ranging from 0.65 to 1.29 with Eu/Eu* ranging from 0.49 to 0.91 suggesting mafic-ultramafic source rocks in the provenance.
On the other hand, the Post QPC (PQPC) rocks are characterised by LREE enrichment with (La/Sm)N ranging from 2.66 to 7.07, nearly flat HREE with (Gd/Yb)N ranging from 0.58 to 0.95 and significant depletion of Eu with Eu/Eu* ranging from 0.34 to 0.85, indicating felsic province
in the source area. The conglomerates and quartzites representing the QPC are showing mixed nature of these, reflecting the
transitional character in depositional environment. Increase in abundance of REE, K2O/Na2O, Th/Sc, La/Sc, Th/U, Hf/Ta and Zr/Y ratios are characteristic of the QPC. The PQPC sediments are enriched in Th, U and HFSE
like Hf, Nb, Zr and Y, and depleted in Co and Eu than their older counterparts. These geochemical signatures signify the dominance
of mafic-ultramafic rocks in the source area for Sargur rocks and the existence of granite-granodiorite for PQPC clastics.
Thus, the unconformity related oligomictic quartz pebble conglomerates (QPC) and quartzites at the base of Bababudan Group
resembling the QPC of Witswaterand, South Africa signifies that a stable continental crust had already developed in southern
India prior to ∼3.0Ga. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|