A comparative study of the Precambrian Sonakhan(SGB)and Mahakoshal(MGB)greenstones belts of Central India has been undertaken to decipher their provenance,paleoweathering,paleogeography,and tectonics.As compared to th...A comparative study of the Precambrian Sonakhan(SGB)and Mahakoshal(MGB)greenstones belts of Central India has been undertaken to decipher their provenance,paleoweathering,paleogeography,and tectonics.As compared to the Upper Continental Crust(UCC),the MGB samples are enriched while the SGB samples are depleted in mafic elements indicating the presence of mafic rocks in the source of the MGB.This is complemented by the Ni–Cr diagram.The REE concentrations,LREE fractionated patterns and negative Eu anomalies of the MGB and SGB samples indicate derivation of sediments from a highly fractionated granitic source.Since MGB samples also contain the geochemical signature of mafic rocks,it is,therefore proposed that the MGB clastic load were derived from two sources(mafic+felsic)with arc character.This is attested by Cr and Zr relationships,and LILE enrichment,and HFSE depletion.These features suggest that the SGB developed as autochthonous while the MGB developed as an allochthonous belt.The chemical alteration indices such as chemical index of alteration(CIA),plagioclase index of alteration(PIA),and index of compositional variability for MGB samples indicate that they were dominantly derived as the first cycle(with minor recycled)sediments from bimodal sources(dominantly continental arcs)by intense chemical weathering as compared to the SGB samples,which were derived from felsic sources(dominantly cratonic rocks),and partly by recycling through a low chemical weathering.The CIA and PIA values of the samples reveal a change in the climatic conditions from Late Archean to Late Paleoproterozoic.Such change is interpreted in terms of migration of the Indian plate from high latitudes in the Late Archean to lower latitudes during the Late Paleoproterozoic.This is consistent with the paleomagnetic data that placed India in the configuration of 2.45 Ga Ur and 1.78 Ga Columbia supercontinents.展开更多
基金the financial support from UGC,Govt.of India in the form of a research project F.No.40-304/2011(SR)the Department of Science and Technology,Govt.of India for financial support in the form of a Research Project(SR/S4/ES-180/2005)。
文摘A comparative study of the Precambrian Sonakhan(SGB)and Mahakoshal(MGB)greenstones belts of Central India has been undertaken to decipher their provenance,paleoweathering,paleogeography,and tectonics.As compared to the Upper Continental Crust(UCC),the MGB samples are enriched while the SGB samples are depleted in mafic elements indicating the presence of mafic rocks in the source of the MGB.This is complemented by the Ni–Cr diagram.The REE concentrations,LREE fractionated patterns and negative Eu anomalies of the MGB and SGB samples indicate derivation of sediments from a highly fractionated granitic source.Since MGB samples also contain the geochemical signature of mafic rocks,it is,therefore proposed that the MGB clastic load were derived from two sources(mafic+felsic)with arc character.This is attested by Cr and Zr relationships,and LILE enrichment,and HFSE depletion.These features suggest that the SGB developed as autochthonous while the MGB developed as an allochthonous belt.The chemical alteration indices such as chemical index of alteration(CIA),plagioclase index of alteration(PIA),and index of compositional variability for MGB samples indicate that they were dominantly derived as the first cycle(with minor recycled)sediments from bimodal sources(dominantly continental arcs)by intense chemical weathering as compared to the SGB samples,which were derived from felsic sources(dominantly cratonic rocks),and partly by recycling through a low chemical weathering.The CIA and PIA values of the samples reveal a change in the climatic conditions from Late Archean to Late Paleoproterozoic.Such change is interpreted in terms of migration of the Indian plate from high latitudes in the Late Archean to lower latitudes during the Late Paleoproterozoic.This is consistent with the paleomagnetic data that placed India in the configuration of 2.45 Ga Ur and 1.78 Ga Columbia supercontinents.
