Integration of Geophysical and Geological Data of Kimberlites in Narayanpet–Maddur Field, Andhra Pradesh, India

Abstract

The Archean Dharwar craton of India hosts well-known kimberlite fields. The present study area around Narayanpet–Maddur in Andhra Pradesh of South India is a part of the eastern Dharwar craton with ~34 known kimberlite bodies (1400–1080 Ma) that form three clusters. Geophysical studies help to decipher the tectonically complex nature of the area. Regional gravity and magnetic anomaly maps show the subsurface structures in the area depending on the density and susceptibility contrasts respectively. The eastern and western parts of the study area are comprised biotite granite and migmatite gneisses that are separated by a prominent NW–SE trending schist belt that is reflected in both the gravity and magnetic data. Based on the geophysical data, this belt is likely to be the result of basement faulting. Other NW–SE trending deep-seated faults are clearly delineated in both geophysical maps. Along with NW–SE trending major faults, E–W, NE–SW and N–S linear trends indicate structural disturbances, and the intersections of lineaments are likely favorable locations for the emplacement of the kimberlites. Magnetic anomalies are more effective in the identification of faults, fractures and dykes in the granitic terrains. Application of various digital filters to the geophysical data clearly indicates that anomalies correlate with the known surface geology and provide information about the shallow and deeper subsurface features. The analytical signal map demarcates the weathered and unweathered pipes based on the intensity of magnetization.Gravity and magnetic 2D forward modeling of profiles across the Narayanpet, Maddur and Kotakonda clusters reveals intrusive bodies in the host rock and the structural features in the area. Both models correlate with each other in terms of the subsurface geology and the depth of intrusive bodies. Euler deconvolution depth estimation for gravity and magnetic data brought out the location and depth of dykes as well as new potential kimberlite areas to the north of Maddur and in the NE and SW portions of schist belt. These potential areas lie within a conjugate system of fractures and faults, some of which may have been reactivated.