A Classification of Thrust Fronts

Abstract

Variations in structural style at thrust fronts are examined to determine whether they represent different stages of typical thrust sheet development or unique events as orogenic stresses declined. Thrust fronts are classified as buried or emergent, in which either the sole thrust died out in the subsurface or emerged to the synorogenic surface. Buried thrust fronts are subdivided into two types: type 1 fronts end in broad zones of low strain; type 2 fronts end in zones of high strain. Emergent thrust fronts may display significant horizontal displacement (strongly emergent) or limited displacements of about 1 km (weakly emergent). Tip-stick thrust fronts exhibit high strains and out-of-sequence thrusting. Different types of thrust fronts are linked by transitional tip-li e anticlines and strike-slip zones. Most thrust front types represent different stages of typical thrust sheet development, but those in type 1 display atypical development unique to thrust fronts.