Strain patterns in Archaean dome-and-basin structures: The Dharwar craton (Karnataka, South India)

Models simulating the role of gravity in the Earthʹs crust are the main source of criteria used for the field identification of diapirs. After a short review of the distribution of finite strain in experimental diapir models, we describe an example where differential erosion of a tilted craton has provided 3D geometrical information on patterns in a diapiric system at various depths (from greenschist to granulitic facies conditions) within the Archaean continental crust of the Dharwar craton, South India. Diapirs and anti-diapirs (‘sagducted’ greenstones) are observed at different levels: structures and strain are consistent with all the field identification criteria inferred from experimental simulation, but some peculiar structural features are also observed which are not predicted by the models. These features, such as strain trajectory triple junctions, result from (i) the progressive deformation of diapiric domes or sagducted basins, (ii) interferences between diapiric structures (body forces) and (iii) the superimposition of diapiric strain fields on regional horizontal shortening (boundary forces).