Estimation of Crustal Tilting from Petrotectonic Interpretation of Mesozone Granitoid and its Marginal Parts, Eastern Dharwar Craton, India

Abstract

The outcrops of greenstone belt and granite complex along Ramagiri-Penakacherla tract are analyzed for tectonics and associated deformation history related to crustal evolution. Field data connote more than five deformation events. Initial ductile deformation regime (D₁-D₄) passes through brittle-ductile (D₅) to shallow brittle regime (D₆). Multiple deformation events (D₁-D₅) resulted in shear zones with variable trends and sense. Three major generations of folding (F₂–F₄) imprinted over and obscure F₁ folding in ductile regime. Younger granite intruded after F₃ hence exhibit only F₄ folds. Brittle regime (D₆) is manifested by faults with dominant E-W trend affected all earlier deformation features. They show mainly normal and few strike slip motion with episodic reactivation with dominantly N-S stretching (i.e., σ₃). Contact relationships between granite and country rocks give insight on depth and associated pressure-temperature condition. From deeper catazone through intermediate mesozone to shallow epizone granite the progressive increase in temperature contrast influence contact relationships with country rocks from concordant through gradational to sharp discordant. Structural attributes of the northern and southern end of the study area exhibit remarkable changes in granite character, which give information on changes in crustal depth. Supportive petro-mineralogical and geochemical evidences also imply for exhumed northerly tilted crust. Bhima and Kaladgi basins are developed due to this crustal block tilting and basin fill sediments were supplied from erosion of uplifted southern parts. During erosion, the exhumation leads to retrograde metamorphism which is better manifested in metabasic rocks. From the surface distance between epizone/mesozone and mesozone/catazone boundaries and average crustal depth difference between these two boundaries, a northerly tilt angle of 1.9⁰ is estimated. The obduction at the southern end of Dharwar Craton and late stage N-S stretching is responsible for such tilting.