Paleoweathering and composition of source of clastic sedimentary rocks of Archean Jamda-Koira basin, Singhbhum Craton

Borgayary, Rupham (2022) Paleoweathering and composition of source of clastic sedimentary rocks of Archean Jamda-Koira basin, Singhbhum Craton. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Rupham Borgayary (17MS221)) 17MS221_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (5MB)

Abstract

It has always been a challenge to understand the early conditions of the Earth. A major part of the crust formed during the Archean has been destroyed either by erosion, subduction or other processes. The processes of formation of sedimentary rocks and the condition of deposition were possibly different in the Archean as compared to the present since the surface environment was different. This work tries to address some of these problems. It includes petrography and geochemical studies to understand the composition of the source rocks that contributed sediments to the Archean Jamda-Koira basin, Singhbhum Craton. This work aims to investigate the weathering pattern of the source rocks during the Archean. The shale and sandstone samples collected from the basin have moderate to high CIA values (74 - 99). This fact indicates that the source rocks of these sediments were under intermediate to extreme weathering conditions. High values of elemental ratios like Th/Sc, La/Sc, La/Cr suggests a source dominated by felsic rocks (mostly granitoids). A few samples indicate significant contribution from mafic sources though. The shales and sandstones are characterized by enriched LREE pattern, negative Eu anomalies and flat HREE pattern. Some shale samples display negative cerium anomalies. The REE pattern suggests that the source rocks of the sedimentary rocks of the Jamda-Koira basin originated from shallow crustal melting. The Ce anomalies suggest that the sediments were deposited in an oxidizing environment.

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