Deformation patterns in the Jonk Conglomerate of the Sonakhan greenstone Belt, Bastar Craton, India, with evidence of transpressional deformation

The Bastar Craton, a Paleoarchean Precambrian shield in Central India, hosts the Sonakhan Greenstone Belt, which includes the Jonk Conglomerate. This clast-supported, poorly sorted (clast sizes range between 0.5 and 58.0 cm), polymictic metaconglomerate is exposed over an area of 18 km x 16 km along the Jonk river. It displays a crude NNW-SSE foliation parallel to the greenstone belt fabric. Petrography reveals greenschist-facies metamorphism (chlorite, sericite), while clast aspect ratios and structural analysis show horizontal sinistral shear and vertical normal compression. Vertical sections further indicate westward upthrown movement, suggesting thrust-driven uplift. Sigma- and delta-type clasts with recrystallized quartz tails reflect progressive non-coaxial strain. Finite strain analysis (Rf/φ, Fry methods) and a Flinn diagramconfirm flattening-dominated deformation. Vorticity analysis (PHD method) yields a vorticity number (Wk) of 0.917, consistent with general shear (transpression) combining pure and simple shear. This regime generated oblique sinistral kinematics, aligning with regional tectonics. Previous studies propose multi-phase deformation of the Bastar Craton: initial N–S compression followed by E–W thrusting. The Jonk Conglomerate’s transpressive fabric, sinistral shear, and flattening-dominated strain suggest it primarily records the later E–W thrusting phase, overprinting earlier structures. Its structural-metamorphic signature thus positions it as a critical archive of the Bastar Craton’s Paleoarchean evolution, marked by polyphase deformation during greenstone belt stabilization.