Precambrian mafic magmatism in the Bastar craton,central India |
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| Authors: | Rajesh K Srivastava Gulab C Gautam |
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| Institution: | (1) Igneous Petrology Laboratory, Department of Geology, Banaras Hindu University, Varanasi, 221 005, India |
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| Abstract: | The Bastar craton has experienced many episodes of mafic magmatism during the Precambrian. This is evidenced from a variety
of Precambrian mafic rocks exposed in all parts of the Bastar craton in the form of volcanics and dykes. They include (i)
three distinct mafic dyke swarms and a variety of mafic volcanic rocks of Precambrian age in the southern Bastar region; two
sets of mafic dyke swarms are sub-alkaline tholeiitic in nature, whereas the third dyke swarm is high-Si, low-Ti and high-Mg
in nature and documented as boninite-norite mafic rocks, (ii) mafic dykes of varying composition exposed in Bhanupratappur-Keskal
area having dominantly high-Mg and high-Fe quartz tholeiitic compositions and rarely olivine and nepheline normative nature,
(iii) four suites of Paleoproterozoic mafic dykes are recognized in and around the Chattisgarh basin comprising metadolerite,
metagabbro, and metapyroxenite, Neoarchaean amphibolite dykes, Neoproterozoic younger fine-grained dolerite dykes, and Early
Precambrian boninite dykes, and (iv) Dongargarh mafic volcanics, which are classified into three groups, viz. early Pitepani
mafic volcanic rocks, later Sitagota and Mangikhuta mafic volcanics, and Pitepani siliceous high-magnesium basalts (SHMB).
Available petrological and geochemical data on these distinct mafic rocks of the Bastar craton are summarized in this paper.
Recently high precision U-Pb dates of 1891.1±0.9 Ma and 1883.0±1.4 Ma for two SE-trending mafic dykes from the BD2 (subalkaline)
dyke swarm, from the southern Bastar craton have been reported. But more precise radiometric age determinations for a number
of litho-units are required to establish discrete mafic magmatic episodes experienced by the craton. It is also important
to note that very close geochemical similarity exist between boninite-norite suite exposed in the Bastar craton and many parts
of the world. Spatial and temporal correlation suggests that such magmatism occurred globally during the Neoarchaean-Paleoproterozoic
boundary. Many Archaean terrains were united as a supercontinent as Expanded Ur and Arctica at that time, and its rifting
gave rise to numerous mafic dyke swarms, including boninitenorite, world-wide. |
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| Keywords: | Mafic magmatism Dykes Volcanics Precambrian Bastar craton Central India |
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