The Doonerak multiduplex of the central Brooks Range fold and thrust belt in arctic Alaska developed during footwall collapse beneath the Amawk thrust, which underlies the Endicott Mountains allochthon. The Endicott Mountains allochthon transported Devonian clastic rocks northward over a footwall composed of lower Paleozoic clastic and volcanic rocks of the Apoon assemblage and uppermost Devonian to Carboniferous clastic and carbonate strata. The geometry and kinematic development of the Doonerak multiduplex differ from typical duplex models in that the Doonerak example consists of two stacked duplexes that formed simultaneously. The upper duplex (the Blarney Creek duplex) and the lower duplex (the Apoon duplex) are separated by the Blarney Creek thrust zone, which served both as the floor thrust of the upper duplex and as the roof thrust of the lower duplex. The intervening fault zone between the two stacked duplexes changes character along strike, from that of a sharp tectonic contact to a diffuse zone of distributed shear up to 250 meters thick. In most locations, the fault zone is tens of meters thick and characteristically contains deformed conglomerate. The stratigraphic position of the fault zone was controlled by a thin conglomerate unit which forms the interface between the Apoon assemblage and the overlying clastic and carbonate rocks. The fault zone truncates structures at the base of the upper duplex and at the top of the lower duplex, locally omitting up to 30 meters of section. Where it is broadest, the Blarney Creek fault zone contains interleaved thin slices of both upper-duplex and lower-duplex lithologies.