Neoarchean gabbroids of the Southern Bundelkhand terrane, Bundelkhand Craton: new geochronology data and geodynamic settings

Mafic magmatism is an important indicator of large-scale thermal events associated with the involvement of the mantle. It is also common in Archean cratons, including those of the Indian Shield, and is used for correlation of endogenic activity in them. Distinguished in the Bundelkhand Craton, which is part of a northern group of Indian Shield cratons, is Archean mafic magmatism, which took place before Neoarchean (2.5 Ga) cratonization, and Paleoproterozoic magmatism. The Lalitpur group of gabbroic rock massifs, which has not been studied previously, was revealed in the western South Bundelkhand terrane of the Bundelkhand Craton. The gabbroic rocks are cut by Neoarchean granites and are, therefore, Archean. The massifs consist of leucocratic amphibole gabbro to diorite, and display coarse-grained structure but no signs of layering. The gabbro contains zircon occurring as semi-transparent to transparent palebrown crystals of elongated prismatic habit. The grains are very coarse, varying in size from 200 to 500 μm. Mineral inclusions in the zircon are abundant. They consist of amphibole, pyroxene, plagioclase, quartz and apatite. The zircon grains were dated using the laser ablation method (LA-ICP-MS). The isotopic age of the late stage in the formation of the massifs is 2551 ± 5 Ma. Neither individual grains nor older cores in the zircon grains analyzed have been found. Thus, the age of the gabbroic rocks in the Lalitpur group of massifs is comparable with that of subduction volcanism in the Central Bundelkhand terrane. The geochemical features of the gabbroic rocks suggest that their formation is also associated with subduction geodynamics. The above mafic intrusions were probably formed in the suprasubduction zone of an active continental margin.