Provenance of the conglomerate and siliciclastic rocks from the Gadag Greenstone Belt, Western Dharwar Craton, India: Implications for understanding Neoarchean basin margin sedimentation

• Published in: Geological journal (Chichester, England) England), 2023-05, Vol.58 (5), p.1911-1944
• Main Authors: Pratihari, Asim Ranjan, Hegde, Venkatraman S., McKenzie, N. Ryan, Frimmel, Hartwig E., Shukla, Anil D., Hulaji, Shivani
• Format: Article
• Language: English
• Subjects: basin margin sedimentation; Belts; Chert; Chlorite; Conglomerates; Cratons; detrital zircon dating; Europium; Feldspars; Fractionation; Gadag Greenstone Belt; geochemistry; Geochronology; Greywacke; Isotopes; Plate tectonics; polymictic conglomerate; Quartzite; Radiometric dating; Rare earth elements; Rock; Rocks; Scandium; sediment provenance; Sedimentation; Sedimentation & deposition; Siltstone; Tectonics; Thorium; Transition elements; Weathering; Western Dharwar Craton; Ytterbium; Zircon
• ISSN: 0072-1050; 1099-1034
• DOI: 10.1002/gj.4699

Petrographic, whole‐rock geochemical and geochronological analysis of polymictic conglomerate, associated siltstone and greywacke in the Neoarchean Gadag Greenstone Belt in the Western Dharwar Craton, India, provides new insights into sedimentary provenance and tectonic setting. The polymictic conglomerate contains granitic, gneissic, felsic and mafic volcanic, quartzite and banded ferruginous chert clasts within a quartzo‐feldspathic matrix. Framework grains in the siltstone and greywacke are quartz, feldspar with rock fragments, embedded in a chlorite‐dominant matrix. The chemical index of alteration values (~70) and A‐CN‐K plot for the rocks suggest a low‐to‐moderate degree of weathering. Rare earth element (REE) patterns show moderate fractionation (LaN/YbN ~ 12.31) with a weak negative europium anomaly (0.82). Enrichment in transition elements (Ni, Cr, Co, Sc) and depletion in high‐field‐strength elements, as well as relatively low La/Co (0.62), moderate to high Th/Yb (3.06), La/Th (5.16), La/Yb (17.5), and La/Sc (~2.37) ratios, suggest a mixed felsic‐mafic provenance. U–Pb dating of detrital zircon from the conglomerate and greywacke revealed major age peaks at ca. (3.2, 2.9, 2.8, 2.6, 2.5 Ga) and a maximum age of deposition of 2,508 ± 26 Ma, 2,493 ± 20 Ma, respectively. The above data suggest low to moderately weathered proximal sources for both conglomerate and greywacke, indicating that these two rock types were not deposited simultaneously, but rather separately. The association of these conglomerates and greywacke with continental arc‐related volcanics indicates the closing of an arc at the time of sedimentation. Complex provenance consisting of recycled and magmatic arc during basin closure confirm the notion of modern style plate tectonics operating during Neoarchaean. Petrography, geochemistry, and geochronological data were used to investigate the provenance of the Neoarchean siliciclastic rock sequence from the Majjur and Attikatti Domains of the Gadag Greenstone Belt, Western Dharwar Craton, India. A mixed approach suggests moderately weathered proximal sources deposited in the backarc setting. Geochronological data revealed a new maximum age of sedimentation, whereas a combined method of modal proportion of the various clasts with rare earth element mixing calculations is used to show a complex mixed felsic‐mafic provenance.