Brittle failure mode plots for compressional and extensional tectonic regimes

Equations governing different macroscopic modes of brittle rock failure (extensional fracturing, extensional-shear fracturing, compressional shear failure and reshear of existing faults) can be represented on plots of differential stress vs effective vertical stress for a set of material properties. Such plots can be constructed for different tectonic regimes and correlated to depth for particular fluid pressure conditions, allowing easy evaluation of the physical controls on brittle rock failure, and ready comparison of the fields occupied by the three failure modes in different tectonic settings. They emphasize the relative ease, in terms of differential stress and fluid-pressure levels, of deforming a rock mass by brittle fracturing and faulting in extensional regimes compared with compressional. Aside from their relevance to general structural mechanics, these generic failure plots have wide-ranging application to understanding the initial development and progressive evolution of fault–fracture systems, both in sedimentary basins and as hosting structures for hydrothermal mineralization in different tectonic settings.