Stress enhanced tensile fractures in elliptical clast in conglomerate

Abstract

Mode-I fractures within the elliptical clasts from Archaean age Chitradurga Schist Belt (Dharwar craton, south India) are analyzed to decipher the paleostress condition. These fractures are characterized as systematic, steeply dipping and parallel to each other. The analysis is performed in three steps – (1) fixing and transforming of the coordinate systems to describe the elliptic domain under far-field stress, (2) proposing suitable complex potentials for inclusion and matrix followed by the plane strain solution for elliptical domain to fractured clasts, (3) obtaining the state of stresses readily inside the inclusion. We conclude that the mode-I fractures in elliptical clasts are developed due to far-field stress enhancement inside the rigid clasts at shallow depth. The deduced paleostress conditions also fit very well with the orientation and sense of previously revealed regional tectonics. We infer that the amplification of stresses in the rigid inclusions is function of elastic moduli of the clast and matrix, ellipticity of the clasts and remote stresses. We interpret that the enhanced intra-clast differential stresses are more for the clast with higher aspect ratio; thus is more susceptible for tensile fracturing, than the lower one for a constant applied far-field stresses. We also estimate the minimum breakage loads as well as minimum depths, required for the clasts of different aspect ratio to develop tensile fractures in them. We imply that fractured elliptical clasts can be regarded as an important paleostress indicator.