Basement–cover structural relationships in the Kaladgi Basin, southwestern India: Indications towards a Mesoproterozoic gravity gliding of the cover along a detached unconformity

Illite crystallinity index from the Mesoproterozoic sedimentary cover of the Kaladgi basin, southwestern India: Implications on crustal depths of subsidence and deformation

“…The total thicknesses of the Mesoproterozoic sediment cover of the Kaladgi basin is 4234 m. The Mesoproterozoic cover of the Kaladgi basin is reported to have been deformed into elongated regional dome-and-basin patterns that are oriented from WNW-ESE to E-W. Deformation is relatively intense in the south-central sectors of the basin and mild to almost no deformation in the northern margins (Jayaprakash et al 1987; Jayaprakash 2007) (figure 2). The deformational architecture of the basin and the structural details of the deformed Mesoproterozoic cover rocks have been comprehensively documented recently and explained in terms of basement-cover structural relationships and the origin of deformation of the cover (Mukherjee et al 2016). On the basis of type, geometry, distribution, association of structural elements, variation and relative chronology of development, the deformation structures of the Mesoproterozoic sedimentary cover rocks of the basin can be grouped to define an extensional domain in the northern sectors and a contractional domain in the south-central sectors of the basin (Mukherjee et al 2016) (figure 2).…”

“…The deformational architecture of the basin and the structural details of the deformed Mesoproterozoic cover rocks have been comprehensively documented recently and explained in terms of basement-cover structural relationships and the origin of deformation of the cover (Mukherjee et al 2016). On the basis of type, geometry, distribution, association of structural elements, variation and relative chronology of development, the deformation structures of the Mesoproterozoic sedimentary cover rocks of the basin can be grouped to define an extensional domain in the northern sectors and a contractional domain in the south-central sectors of the basin (Mukherjee et al 2016) (figure 2). The extensional domain is characterised by development of a gently dipping (10 • -15 • due south) homocline that is affected at places by normal faults, tensile and hybrid joints and contain widely separated segments of the cover that are apparently extensional tear-apart of the cover across strike (Mukherjee et al 2016).…”

“…On the basis of type, geometry, distribution, association of structural elements, variation and relative chronology of development, the deformation structures of the Mesoproterozoic sedimentary cover rocks of the basin can be grouped to define an extensional domain in the northern sectors and a contractional domain in the south-central sectors of the basin (Mukherjee et al 2016) (figure 2). The extensional domain is characterised by development of a gently dipping (10 • -15 • due south) homocline that is affected at places by normal faults, tensile and hybrid joints and contain widely separated segments of the cover that are apparently extensional tear-apart of the cover across strike (Mukherjee et al 2016). In the south-central sectors of the basin, an association of WNW-ESE trending, both northerly and southerly verging, asymmetric-to-overturned, plane non-cylindrical, gently plunging folds with axial planar cleavages, E-W trending thrusts and N-S trending strike-slip faults, together define the contractional domain.…”

“…directed gravity gliding of the cover over the basement along the basement-cover contact (unconformity) that served as a surface of detachment (Mukherjee 2013Mukherjee et al , 2016. The gravity gliding of the cover rocks produced an updip extensional zone and a downdip contractional zone as described above.…”

“…Aggradation of IC index due to layer parallel contractional deformation involving all stratigraphic units simultaneously would produce similar metamorphic grades. The older Muttalgeri argillites, whose temperatures were relatively low (high IC index) compared with the young Hoskatti argillites, were collected from the zone of extension in the northern sector and the Hoskatti argillites were from the contractional zone corresponding to the deformed south-central sectors of the basin, which bear prominent development of penetrative cleavage that are axial planar to the map scale and mesoscale folds (Mukherjee et al 2016). The same Muttalgeri argillites show a low IC index value along with the southern boundary of the basin in the contractional zone.…”