A new ca. 1.73 Ga mafic magmatic event in the Indian Shield: Evidence from an in-situ SIMS U-Pb baddeleyite date and geochemistry of the mafic intrusions within the Gwalior basin, Bundelkhand craton

Abstract

A suite of mafic sill intrusions is present in the Gwalior sedimentary basin of the Indian Shield, and is herein dated. An obtained in-situ SIMS U-Pb baddeleyite date of 1733 ± 23 Ma, represents a new mafic magmatic event in the Bundelkhand craton, in particular, and in the Indian Shield, in general. Gwalior mafic sill samples are typically doleritic in nature and show ophitic or sub–ophitic textures. Their geochemical characteristics classify them as sub-alkaline high-iron tholeiitic basalts. Geochemistry suggests emplacement of these mafic sills in a within-plate setting and derived from a melt originated from a subduction-zone-modified lithospheric mantle (SZLM) source in spinel-garnet transition zone. Mafic magmatic/LIP events of the same age (i.e., ca. 1.73 Ga) are known only from the North China, North Australia and Siberian cratons. However, the date uncertainties would allow matches over the range of 1756–1710 Ma, and additional blocks that could be relevant include Laurentia, West Africa, East Antarctica, and Sao Francisco cratons. Based on the new U-Pb Gwalior sill age and other available ages on the basement rocks and sedimentary units, it is suggested that the Gwalior sediments were deposited between 1980 and 1710 Ma.