Evolution of fractures and tertiary fold-and-thrust deformation in the central Brooks Range foothills, Alaska

Abstract

Fractures form in foreland basin rocks during their progressive incorporation into fold-and-thrust deformation and subsequent uplift. This study investigates the relationship between fracture distribution and the evolution of the fold-and-thrust belt. This study identifies four fracture sets in pre-orogenic carbonates of the Brooks Range northward into foreland basin. Fracture distribution, structural style, and apatite fission-track (AFT) data define four structural domains. Domain I consists of strongly deformed Mississippian through Triassic rocks. Fracture sets 1, 2 and 4 are present in domain I, reflecting Valanginian through early Tertiary deformation. Domains II-IV consist of clastic basin deposits hosting fracture sets 2-4. Domains II and IV share fracture set distributions (sets 3 and 4), AFT cooling ages (70-60 Ma) and deformational style of open ~symmetric detachment folds. Domain III includes fracture sets 2-4, AFT cooling ages of ~100 Ma, reflecting thermal immaturity and south-vergent structures consistent with back thrusting. Restoration of early Tertiary deformation is constrained by surface, seismic and thermal data. Reconstruction shows the importance of back thrusting within domain III during the early Tertiary, the northern extent of the orogenic wedge, and the relationship between fold-and-thrust deformation and the relative timing and distribution of fracture sets in the Brooks Range foothills.