STRUCTURE, PALEOGEOGRAPHY, AND EXTENSIONAL FOUNDERING OF THE KINGMAN UPLIFT, NORTHWEST ARIZONA AND SOUTHEAST NEVADA

The Kingman uplift is a north-plunging Laramide-age uplift between the Colorado Plateau and eastern edge of the Cretaceous-age Sevier thrusts. The uplift post-dates intrusion of ~ 70 Ma plutons and is earlier than or synchronous with carving of paleocanyons containing sediments as old as Paleocene. The flanks of the uplift exhibit a gentle progressive beveling of the lower and middle Paleozoic section. However, the Upper Permian Kaibab and Toroweap Formations form a SW-facing scarp, visible on the north side of the Grand Canyon where it has retreated no more than about 8 km to the northeast since ~ 19 Ma. Before Miocene extension, the paleoscarp continued around the north-plunging axis of the arch and formed a topographic barrier. In the core of the uplift Oligocene-Miocene volcanic and sedimentary rocks overlie Proterozoic basement south of the paleoscarp, whereas the pre-extension Oligocene Rainbow Gardens Member of the Horse Spring Formation overlies mostly Mesozoic sedimentary rocks north of the paleoscarp.

Paleocanyons cut into the SW Colorado Plateau contain Paleocene and Oligocene fill, capped by ~ 18-20 Ma volcanic rocks that were sourced west of the plateau and deposited eastward across the beveled surface. Therefore, the uplift was still high relative to the plateau at 18 Ma. The Peach Springs paleocanyon is the deepest and broadest. A similar ENE-trending paleovalley lies between the Cerbat and Hualapai Mountains at Kingman. Surface profiles of these two paleovalleys are strikingly similar in width and depth and are herein correlated.

The northern Grand Wash and Cerbat Mountain faults may represent reactivated west-dipping Laramide reverse faults, separating a terrane of two-mica, garnet-bearing 64 -73 Ma plutons intruded as much as 10 km deep from similar age but shallowly intruded plutons east of these faults. If so, the faults formed a steep east side to the north-plunging uplift just west of Kingman and most likely lost displacement northward; the paleocanyons may have originated along the faulted east front of the uplift and have relatively local sources. The highest part of the Kingman uplift subsequently foundered and evolved into the northern Colorado River Extensional corridor, as large-magnitude extension ripped across the central part of the highlands beginning ~ 16 Ma.