Fold-Thrust Belt Architecture and Structural Evolution of the Northern Part of the Nallamalai Fold Belt, Cuddapah Basin, Andhra Pradesh, India

Abstract

Two major structural events characterize the tectonic evolution of the northern part of the Nallamalai Fold Belt (NFB): (1) the Late Paleoproterozoic or Early Mesoproterozoic Dn1 compression due to the thrusting of granitic gneiss and Nellore Schist Belt (NSB) over the eastern part of the NFB possibly related to the Columbia supercontinental activities; and (2) the Late Neoproterozoic-Early Cambrian Dn2 deformation in the NFB due to its overthrust movement on the western and northern part of the undeformed Cuddapah basin (i.e., the Kurnool and the Palnad sub-basins). The late structures with NW to N vergent hanging wall lithounits (NFB) are represented by several map-scale imbricate thrust sheets, flat and ramp structures, asymmetrical to overturned folds, and structures associated with nappe. The nature of deformation in the footwall (Kurnool Group in Palnad sub-basin) and the hanging wall (NFB) structures are also elaborated in view of the possible regional tectonics. Progressive oroclinal model is also proposed here to explain the changes in the structural trend of NFB from NE to E. The variations of the NFB structures in conjunction with the regional structures connotes of thin-skinned deformation during Pan-African period, which are examined to constrain the possible plate kinematics related to the convergence of East Gondwana fragments.