Geochronology, whole-rock geochemistry and Sr-Nd isotopes of the Bhanupratappur mafic dyke swarm: Evidence for a common Paleoproterozoic LIP event at 2.37–2.36 Ga in the Bastar and Dharwar cratons

Abstract

Mafic dykes and dyke swarms in continental settings provide information on the evolution of the subcontinental mantle and can be key elements in the reconstruction of paleo-geographic settings of now separated crustal terranes. This study focuses on the petrogenesis and geochronology of mafic dykes of the WNW (~125°) trending Bhanupratappur swarm in the central Bastar Craton, central India. Dykes of the Bhanupratappur swarm yield an average U-Pb (ID-TIMS) baddeleyite age of 2360 ± 4 Ma, which is interpreted as their emplacement age. The compositions of the dykes range from tholeiitic basalt to basaltic-andesite. Their rare earth element and multi-element patterns indicate the involvement of a crustal component in their petrogenesis. The whole rock initial 87Sr/86Sr2360 Ma ranges from 0.70097 to 0.70506 with most being more radiogenic than the contemporaneous undifferentiated mantle reservoir (i.e. 87Sr/86Sr2360 Ma = 0.70173). The initial εNd 2360 Ma (+0.85 to −2.7) are chondritic to sub-chondritic. The Sr-Nd Isotope composition and major- and trace element chemistry suggest an enriched-heterogeneous mantle source. The closely matching ages and chemistry of the Bhanupratappur swarm (2360 Ma) and the Karimnagar-Bangalore swarms (2363–2369 Ma) of the Dharwar Craton indicate affinities to a common Large Igneous Province, which further implies that the Bastar and Dharwar cratons were already juxtaposed at 2.37–2.36 Ga. The dykes of the Bhanupratappur (WNW-trending) and Bangalore (E-W trending) swarms converge towards the east indicating a plume center in the east. If the Karimnagar swarm was also linked (and was converging) to the same plume, the present-day mismatch in the orientations of the Karimnagar dykes (NE- to ENE-trending) with the Bangalore and Bhanupratappur dykes may indicate a ~55° counterclockwise rotation of the northern block of the Eastern Dharwar Craton with respect to the southern block after 2.37–2.36 Ga. © 2020 Elsevier B.V.