Fracture and Lineament Patterns across the Midcontinent Indicate Post-Cretaceous Reactivation of Basement-Involved Faults

Abstract

Reactivation of pre-existing weaknesses in the upper crust can be documented using surface features, and has occurred throughout time and space, particularly in regions where the basement material dates from the Precambrian and has undergone successive deformation events. This study aims to use surface features such as fracture patterns to document evidence of such reactivation in the Paleozoic and Cenozoic of Nebraska and Kansas (units separated by an unconformity in the study area). The most prominent basement features in southeast Nebraska and northeast Kansas are oriented NE-SW, likely related to the midcontinent rift, and oriented NW-SE, likely related to fabrics from the Central Plains Orogen. These features are well defined in the potential fields data. Fracture patterns in the study area show an E-W oriented trend, as well as clearly discernable NE-SW and subsidiary N-S and NW-SE trends. The E-W trend is interpreted to be related to far-field stresses from Laramide and Ancestral Rocky Mountain orogenic events, whilst the NE-SW trend is interpreted to be related to subtle reactivation on the Mid-continent rift and related faults, observed in basement data. These movements produced stresses of sufficient magnitude to produce extensional fractures in the overlying rock units, but not sufficient to generate shear. Similarly, the ~N-S and NW-SE fracture trends are taken as evidence of subtle reactivation on the Nemaha Uplift and Central Plains Orogen systems, generating fractures but not shear movement. This contribution therefore provides a convincing case-study of the value of fracture orientations (that is, surface morphodynamics) in discerning buried tectonic trends and subtle reactivation thereon.