Geometry and timing of tertiary deformation of the Dome Rock Mountains, Yuma County, Arizona

Thesis, (M.S.) Geological Sciences.\ud One latitude and one longitude were used on base map.\ud Values taken from Google Earth satellite imagery.\ud Base maps; Dome Rock Mountains, Arizona, and Trigo Peaks, Arizona Quadrangle.\ud Plate 1; Tertiary Geology of the Dome Rock Mountain, Yuma County, Arizona, in back pocket.Mid-Tertiary, extensional deformation is widespread in the detachment terrane of Arizona, California, Nevada, and Sonora. Detachment-related, upper-crustal folding and faulting have been described in ranges throughout this region, so that a general model of mid-Tertiary extension based on the presence and geometry of detachment faults has become generally accepted. Upper-crustal folding, or doming, without the presence of a distinct detachment fault, is also present in the region but has been largely ignored. The Dome Rock Mountains of western Arizona are perhaps the best examples of large-scale doming without the production of a visible detachment fault. Tertiary doming appears to have been deformed by penetratively distributed shear through the well-foliated rocks of the "lower-plate" of the Dome Rock Mountains Mesozoic clastic rocks. "Upper-plate" extension is clearly expressed by normal faulting and tilting of a distinctive Tertiary sequence of redbeds, tuffs, and volcanic rocks. Basin-and-range type normal faulting has also affected the area, creating a major repetition of both Tertiary units, and truncation of the Mesozoic clastic rocks of the Dome Rock Mountains along its steep western margin. Tilting of the "upper-Plate" indicates relative west to southwest transport of the "upper-plate" over inferred detachment faults at depth. Late Miocene alluvial units and the Miocene-Pliocene Bouse Formation are deposited unconformably over the rotated redbed, volcanic, and metamorphic rocks of the Dome Rock Mountains. Deformation by basin-and-range style faulting has rotated the Late Miocene alluvial fan sediments, indicating that extension occurred up to Late Miocene time. Mid-Tertiary crustal extension as displayed in the Dome Rock Mountains may be representative of a hitherto poorly recognized style of detachment-related deformation. Similar styles of deformation appear to have affected other regions containing thick sequences of well-foliated rocks, such as the Pelona-Orocopia Schist terrane of southern California and western Arizona