Abstract

The northeast-, northwest-, and north-northeast-trending basin-range structures that evolved in the late Cenozoic western United States may be explained with a modified version of earlier models within the framework of an intraplate card-deck analogy. Predominantly northwest-trending horst-graben structures began to develop in the southern Basin and Range province during the late Oligocene-early Miocene time (30 to 20 m.y. B.P.) in a wide dextral shear zone extending eastward from the early San Andreas transform fault. Dextral shearing motion in the southern Basin and Range province rotated the entire Colorado Plateau clockwise and opened up the Rio Grande rift in its wake. During Miocene time, dextral shearing continued in the southern Basin and Range province and spread northward into the Great Basin. The Oregon-Nevada lineament and Walker lane were the major dextral wrench faults controlling Miocene deformation in the Great Basin; north-trending pull-apart grabens formed at 45° to these major northwest-trending wrench faults. A transform-fault jump into the Gulf of California 5 m.y. B.P. created the big bend in the San Andreas transform fault that initiated compression along the Transverse Ranges; this squeezed the Mojave fault-bounded block eastward and thus jammed and ended dextral shear deformation in the southern Basin and Range province. Deformation since then has been concentrated in the wide dextral shear zone of the Great Basin.

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