Miocene synextension sedimentation patterns, Whipple Mountains, southeastern California: Implications for the geometry of the Whipple Detachment System

A sedimentary basin formed in the southern and eastern Whipple Mountains during early to middle Miocene detachment faulting. Stratigraphic relations and facies patterns indicate that the shape and size of the sedimentary basin was controlled both by fault activity and by sedimentary processes. High-angle normal faults formed the southwestern, and perhaps also the northeastern boundary of the half graben, whereas a transfer fault probably formed the southeastern boundary. The transfer fault influenced the earliest synextension sedimentation in the basin. The location of this fault and similar faults in the Mohave Mountains and Aubrey Hills of Arizona is inferred to have been controlled by the position of primary irregularities or corrugations of the detachment fault. Shifts in facies patterns, particularly a shift in the position of the basin depocenter, reflect changes in basin geometry. Comparison with adjacent areas is necessary to distinguish between tectonic and nontectonic causes. A shift in depocentral position parallel to regional transport direction in the Whipple Mountains basin is interpreted as resulting from a change in the location of the high-angle normal fault forming the southwestern margin of the basin, whereas a shift perpendicular to transport direction probably resulted from overtopping of topographic barriers within a fault block. The most active phase of faulting occurred prior to deposition of stratigraphic units younger than the 18.5 Ma Peach Springs Tuff. Relative uplift of the core of the Whipple Mountains, probably as a result of isostatic rebound following tectonic denudation, influenced sedimentation patterns after deposition of the Peach Springs Tuff.