Award Date

5-1989

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geoscience

First Committee Member

Eugene I. Smith, Chair

Second Committee Member

Stephen M. Rowland

Third Committee Member

David L. Weide

Graduate Faculty Representative

Diane Pyper Smith

Number of Pages

119

Abstract

The Arch Mountain area of northwestern Mohave County, Arizona, is typified by rocks that range from Precambrian to Quatemary in age. Arch mountain is a north-trending horst bounded on the west by the Petroglyph Wash graben and on the east by the Virgin Basin. A low-angle normal fault, herein named the Arch Mountain detachment fault, is exposed for 6 km along strike just below the ridge crest of Arch Mountain, and it is typified by a 2-20 cm thick zone of hematite-impregnated breccia and cataclasite. The detachment fault places an upper plate of Precambrian gneiss, Paleozoic quartzite, shale and dolomite, and Tertiary intrusive rock on a lower plate composed of quartz monzonite that is geochemically similar to quartz monzonite of the Wilson Ridge pluton. The western margin of the horst is cut by en echelon, west-dipping, high-angle normal faults that step the detachment fault to the west and rotate it to the east. The Ransome fault forms the western boundary of the horst and separates Arch Mountain from Precambrian gneiss and Tertiary volcanics. The eastern margin of the horst is cut by en echelon, east-dipping, highangle normal faults that step the detachment fault to the east and rotate it to the west. The Boulder Wash fault forms the eastern boundary of the horst and separates Arch Mountain from Tertiary Muddy Creek sediments in the Virgin Basin-Detrital Wash area. The Ransome and Boulder Wash faults may be genetically related to and may have formed synchronously with the left-lateral Lake Mead fault system at approximately 12 Ma. Crosscutting relationships indicate that the Arch Mountain detachment fault is older than the Lake Mead fault system. The Arch Mountain detachment fault is possibly related to the development of the Las Vegas Valley shear zone, and it is interpreted to be correlative with the Saddle Island detachment fault. I propose that the Arch mountain detachment fault represents the brittlely deformed, upper crustal part of a regional detachment fault system that has a breakaway zone adjacent to the Grand Wash Cliffs.

Keywords

Arizona; Fault zones; Faults (Geology); Grabens (Geology); Shear zones (Geology)

Disciplines

Geology | Tectonics and Structure

Language

English

Comments

Signatures have been redacted for privacy and security measures.


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