Determnination of fluid pressure conditions using 3D mohr circle in and around G.R.Halli region,chitradurga schist belt, dharwar craton South India

Abstract

In this study, the orientations of 402 quartz veins occurring in metabasalts in and around G.R.Halli region (West Dharwar craton, southern India) are studied and finally used to plot the 3-D Mohr stress circle, which provides information about relative stress/fluid pressure (Pf) conditions, as well as stress state during Pf fluctuation and the formation of these veins. The quartz veins have a wide range of orientations, with two very prominent orientations NNE-SSW and NW–SE striking veins. Vein emplacement is inferred to have taken place under NW–SE compression that is known to have caused late deformation (D3) in the region. 3-D Mohr circle analysis indicates that the driving pressure ratio (R′) was 0.87, which was a high fluid pressure phase and it reactivated previous fractures and finally produced veins with wide range of orientation. The study area has two more clusters of NW–SE oriented and NNE-SSW oriented veins indicationg two more fluid saturation phases. R′ is calculated to be 0.31 and 0.38 from 3-D Mohr circle analysis at low Pf. The whole complex and wide orientation of veins formed in at least three phases. Using unscaled Mohr circle we can get an idea about local stress and fluid pressure condition and how the interplay between them helped in formation of the quartz veins in G.R.Halli region.