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Gautam, Gulab C.
- Geochemistry of Distinct Mafic Intrusive Rocks from Darba-kukanar and Kerlapal-Sukma-Mokhpal Areas, Southern Bastar Craton: Further Data on the Early Precambrian Mafic Magmatism of Central India
Authors
1 Igneous Petrology Laboratory, Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 69, No 6 (2007), Pagination: 1176-1188Abstract
Geochemistry of mafic igneous rocks of early Precambrian age of the southern Bastar craton in and around Darba-Kukanar and Kerlapal-Sukma-Mokhpal areas are presented. Most of these mafic rocks occur as NW-SE trending dykes intruded into the Archaean granitelgranite-gneiss and over metamorphic rocks. Few intrusives also occur as sills or plutonic bodies. On the basis of field relationships between mafic rocks and other exposed rock types and also between the mafic rocks, available geochronological data, petrological and geochemical characteristics, the studied mafic rocks are classified into three main types: (i) Group I (BDI): Mesoarchaean mafic rocks, metamorphosed under mid-amphibolite facies conditions, showing concentration of high-field strength element (HFSE) higher than the Group 3 (boninite-norite) mafic rocks, and lower than the Group 2 (BD2: dolerite-diorite), (ii) Group 2 (BD2): Paleoproterozoic mafic rocks of dolerite-diorite composition, characterized by higher concentration of HFSE than the other two types, and (iii) Group3 (BN: boninite-norite): Neoarchaean mafic rocks, metamorphosed under greenschist-amphibolite transitional conditions, characteristically showing high-Mg and Si, very low-Ti, and HFSE composition close to boninite. These observations are very similar to the previously studied mafic rocks from the other parts of the southern Bastar craton. It is suggested that the BD1 mafic rocks are derived from depleted sub-alkaline basaltic magma, whereas enriched sub-alkaline basaltic magma was responsible for the BD2 mafic rocks. High-Mg boninite-norite (BN) mafic rocks were probably derived from a primary boninitic magma originated from a refractory lherzolitic mantle source. These observations clearly suggest heterogeneous mantle source beneath the Bastar craton during the early Precambrian.Keywords
Geochemistry, Mafic Intrusive Rocks, Boninite, Bastar Craton, Central India.
- Precambrian Mafic Magmatism in the Bastar Craton, Central India
Authors
1 Igneous Petrology Laboratory, Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 73, No Spl Iss 1 (2009), Pagination: 52-72Abstract
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.