Late-Stage High-Angle Faulting, Eastern Doonerak Window, Central Brooks Range, Alaska: ABSTRACT

Abstract

Three deformation phases are recognized in the eastern Doonerak window. From oldest to youngest, they are (1) an isoclinal folding event characterized by pervasive axial-planar slaty cleavage, (2) formation of kink bands and chevron-style folds of the slaty cleavage, and (3) development of gentle flexures with associated crenulation cleavage or close-spaced joint planes. First- and second-phase structures are related to thrust faulting. High-angle faulting may be related to third-phase deformation. Most of these high-angle faults strike west to northwest, are subvertical, and exhibit slickenside striations that plunge gently west. Another set of high-angle faults strikes northeasterly and contains two generations of slickenside striations, a younger subhorizontal set and an older subvertical set. These perpendicular slip directions support the existence of two separate stress regimes: (1) a north-trending principal compressive stress axis, ^sgr1, and (2) a west-trending ^sgr1. Structural analysis of several west-northwest-trending high-angle faults and associated extensional fractures demonstrates a stress regime with ^sgr1 plunging gently west-northwest. This regime is incompatible with north-directed thrusting and supports a separate late-stage deformational event. Two possible interpretations are that the high-angle faulting is (1) related to west-northwest thrusting or (2) is a separate phase of deformation involving significant east-west compression. End_of_Article - Last_Page 675------------