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The Indravati Basin represents an unmetamorphosed and unfossiliferous sequence and shows a broad similarity in lithological association with other Purana Basins of Central India. The carbonates belonging to Indravati Basin have on average, moderately positive δ13 C values (up to +4.5). Numerous successions reported from other parts of world, show similar δ13 C values and contain evidence to suggest that the latest Mesoproterozoic to early Neoproterozoic period may represent an isotopically recognizable interval globally. The elevated δ13 C values of Indravati Basin are also correlatable with other Purana Basins in India including Upper Vindhyan Supergroup. 相似文献
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U. K. Pandey D. V. L. N. Sastry B. K. Pandey Madhuparna Roy T. P. S. Rawat Rajeeva Ranjan V. K. Shrivastava 《Journal of the Geological Society of India》2012,79(1):30-40
The Dargawan gabbros intrusive into the Moli Subgroup of Bijawar Group, yielded Rb-Sr whole rock isochron age of 1967 ± 140
Ma. Based on the oldest age from overlying Lower Vindhyan (1.6Ga) and the underlying youngest basement ages (2.2 Ga), the
time range of Bijawar sedimentation may be assigned as 2.1–1.6 Ga (Paleoproterozoic). Sm-Nd Model ages (TDM), obtained, for Dargawan gabbros, is c. 2876–3145 Ma. High initial 87Sr/ 86Sr ratio of 0.70451 (higher than the contemporary mantle) and negative ɛNdi (at 1.9 Ga) value of −1.5 to − 4.5, indicate assimilation of Archaean lower crustal component by the enriched mantle source
magma at the time of gabbroic intrusion. The dolerite, from Damdama area, which is intrusive into the basement and overlying
sediments of Chandrapur Group in the central Indian craton, yielded Rb-Sr internal isochron age of 1641 ± 120 Ma. The high
initial 87Sr/86Sr ratio of 0.7098 and ɛNdi value of −3.5 to −3.7 (at 1.6 Ga) is due to contamination of the mantle source magma with the overlying sediments. These
dolerites have younger Sm-Nd Model ages (TDM) than Dargawan gabbros as c. 2462–2675 Ma, which is similar to the age of the Sambalpur granite, from which probably sediments
to this part of Chattisgarh basin are derived. Hence mixing of sediments with the Damdama dyke during its emplacement, gives
rise to high initial 87Sr/86Sr and low initial 143Nd/144 ratios for these dykes. The c. 1600 Ma age indicates minimum age of onset of the sedimentation in the Chandrapur Group of
Chattisgarh basin. Both the above mafic intrusions might have taken place in an intracratonic rift related (anorogenic) tectonic
setting. This study is the first reliable age report on the onset of sedimentation in the Chandrapur Group. The total minimum
time span of Chandrapur and Raipur Group may be 1.6 Ga to 1.0 Ga (Mesoproterozoic). The unconformably underlying Shingora
Group of rocks of Chhattisgarh Supergroup thus indicates Paleoproterozoic age (older than 1.6 Ga). Most part of the recently
classified Chattisgarh Supergroup and Bijawar-Vindhyan sequence are of Mesoproterozoic-Paleoproterozoic age and not of Neoproterozoic-Mesoproterozoic
age as considered earlier. Petrographic study of basic dykes from Damdama area (eastern margin of Chattisgarh Supergroup)
indicated presence of primary uranium mineral brannerite associated with goethite. This is the evidence of mafic intrusive
providing geotherm and helping in scavenging the uranium from the surrounding and later alterations causing remobilisation
and reconcentration of pre-existing uranium in host rocks as well as in mafic dyke itself otherwise mafic rocks are poor source
of uranium and can not have primary uranium minerals initially. It can be concluded that mafic dykes have role in uranium
mineralisation although indirectly. 相似文献
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