Deformation Patterns in the Jonk Conglomerate of the Sonakhan Greenstone Belt, Bastar Craton, India with Evidence of transpressional deformation

The Bastar Craton, a Neoarchean Precambrian shield in Central India, hosts the Sonakhan Greenstone Belt, which contains the Jonk Conglomerate—a 18 km x 6 km metaconglomerate exposed along the Jonk River. This clast-supported polymictic metaconglomerate, with clasts ranging from 0.5 cm to 58 cm, displays a NNW-SSE crude foliation aligned with the regional greenstone belt fabric, indicating syn-deformational emplacement during craton assembly.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 diagram confirm 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.Prior studies propose multi-phase Bastar Craton deformation: 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 Neoarchean evolution, marked by polyphase deformation during greenstone belt stabilization.