Thermomechanical origin of regional fracture systems

Regional fracture systems are characterized by subparallel opening-mode fractures formed as a result of brittle deformation in the Earth's crust. Understanding the origin and distribution of these fracture systems is of great practical importance because they can control the flow of underground fluids, such as water, oil and gas, ore-forming fluids, and geothermal fluids. As the world's remaining hydrocarbon reserves continue to be depleted, the rapidly increasing importance of unconventional fractured reservoirs for oil and gas is widely recognized. Here, it is demonstrated that thermal contraction caused by cooling may be an important mechanism for creating tensile fractures in rock during major exhumation events. The extent of this phenomenon is particularly dependent on the magnitude of cooling and on the mechanical properties of the rock. Thermally induced fracture systems are more likely to develop in stiffer rocks, such as well-cemented sandstones and carbonates. The process described herein can be modeled and tested with field data and provides another mechanism to account for and to predict the presence of permeable tensile fractures in the subsurface.