Rawhide Mountains, Mohave County, Arizona, USAi

Regional Level Types
Rawhide Mountains	Mountain Range
Mohave County	County
Arizona	State
USA	Country

ABSTRACT

The Rawhide Mountains, western Arizona, consist of a complexly deformed assemblage of Precambrian metaigneous and metasedimentary, Paleozoic sedimentary, Mesozoic(?) igneous plutonic, and Tertiary sedimentary and volcanic rocks. Precambrian rocks include quartzofeldspathic gneisses of granitic parentage, subordinate impure marbles, and biotite granite. Metavolcanic rocks of Precambrian or Mesozoic age are represented by quartz-sericite and biotite-epidote-quartz schists. Paleozoic sedimentary rocks are quartzites, phyllites, and carbonates. The lowest quartzite and phyllite members are correlated with the Tapeats Sandstone (Bolsa Quartzite) and Bright Angel Shale (Abrigo Formation), respectively. The carbonates are similar to Paleozoic limestones and dolomites in western Arizona, but they are too badly dismembered to make positive correlations. Tertiary rocks include the Artillery (Eocene?) and Chapin Wash (Miocene) Formations. The Artillery Formation is a varicolored sequence of interbedded conglomerates, arkoses, siltstones, limestones, and volcanic rocks. The Chapin Wash Formation consists of red conglomerates, arkoses, siltstones, basalt, and latite. Late Tertiary basalt and Quaternary alluvium comprise the youngest stratigraphic units, which lie unconformably above older rocks.

The structural history of the Rawhide Mountains includes (1) Precambrian intrusion of granitic rocks and the possible extrusion of basaltic to rhyolitic rocks; (2) Mesozoic(?) metamorphism and penetrative deformation of the Precambrian crystalline rocks and overlying Precambrian(?) and Paleozoic rocks; (3) late Tertiary gravity sliding involving Precambrian(?) through Miocene rocks; and (4) latest Cenozoic development of northweststriking oblique dip-slip and reverse dip-slip faults.

Mesozoic(?) deformation is characterized by the development of a metamorphic infra structural complex. Precambrian igneous, sedimentary, and metamorphic(?) rocks that form the core of this complex were metamorphosed to amphibolite grade. Penetrative cataclasis (mylonitization) of these rocks occurred synchronously with late(?) stages of metamorphism. Greenschist-facies metamorphism affected some of the overlying Precambrian(?) metavolcanic and Paleozoic rocks. This deformation resulted in the development of a penetrative cataclastic foliation and a strong N50°E mineral lineation. Major northeast-directed tectonic transport is inferred for this terrane.

The dominant structural feature of the range is the late Tertiary gravity-slide complex. This complex appears to cover more than 1,000 km2 in west-central Arizona. In the Rawhide Mountains the complex is characterized by a chaotic assemblage of Precambrian(?) through Miocene rocks that are separated from underlying mylonitic gneisses by a remarkably sharp basal dislocation surface. Superposition of rock units is primarily younger over older. Almost all of the major rock units are separated from each other by low-angle dislocation surfaces. The chaotic slicing and shuffling of upper-plate rocks has occurred along a complex series of high- and low-angle dislocation surfaces that merge with or are subparallel to the basal dislocation surface. Bedding and foliation in the allochthon typically dip to the southwest at a high angle to the basal dislocation surface. The persistent northwest strike and southwest dip of upper-plate rocks, the geometry of the fault sets, and the orientation of minor structures indicate northeast-directed movement for the slide complex. Gravity sliding occurred between 15.9 m.y. and about 10 m.y. ago.

Latest Cenozoic, high-angle, oblique, normal dip-slip, and reverse dip-slip faulting postdate formation of the gravity-slide complex. The eastern border of the Rawhide Mountains is formed by a major fault with left-lateral dip-slip components. This fault cuts the mylonitic-gneiss terrane and the overlying gravity-slide complex. In the central part of the range, reverse dip-slip faults cut the basal dislocation surface and place mylonitic gneisses on top of isolated slide blocks of Chapin Wash material.

Late Tertiary low-angle deformation is widespread in the Basin and Range Province. Structures in this province previously referred to as late Tertiary thrust faults are here interpreted as gravity slides. The gravity sliding appears to have been the thin-skinned crustal response to the rapid rise of discrete crustal blocks just prior to or contemporaneous with Basin and Range faulting.