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Abstract

Evidence of Cenozoic deformation and sedimentation along the southeasternmost 40 km of the Furnace Creek strike-slip fault zone, in the southwestern Great Basin, is contained in two successions of sedimentary and volcanic rocks. Each indicates a stage in the development of the fault zone and associated basins; each is bracketed by K/Ar age determinations. The older succession, dated at 25 to no less than 14 Ma, occurs in tilted fault blocks of the bordering Funeral Mountains, and predates major crustal extension. The succession is about 1,300 m in maximum exposed thickness, contains remnants of two northeast-sloping alluvial fans, onlaps a Paleozoic basement to the southwest, and includes an unconformity that cuts out progressively older units southwestward. These features indicate that a topographic high persisted where younger formations of the fault-controlled, northwest trending Furnace Creek Basin now occur, and also early vertical movement on the fault zone.

The younger succession, comprising the Artist Drive, Furnace Creek, and Funeral Formations of the basin (McAllister, 1970), ranges in age from about 14 Ma to about 4 Ma. It records the subsidence and deformation of the basin, and was associated with right-lateral slip on northwest-striking faults and with basin-range extension expressed in part by abundant north-to northeast-striking normal faults. The three formations have a composite maximum thickness of about 3,600 m, but the combined thickness varies greatly from place to place, owing to contemporaneous faulting, to changes in depocenters related to the fault movements and to a general thinning southeastward. The sedimentation and faulting also were accompanied by abundant plutonism and volcanism in the Greenwater Range and Black Mountains southwest of the fault zone. The fact that the normal faulting is regional, affecting terranes on both sides of the fault zone, qualifies the Furnace Creek as a special type of divergent strike-slip fault zone.

The contemporaneous strike slip within the 40-km segment of the fault zone probably increases northwestward from zero to no more than a few kilometers, but continues to increase farther northwestward. In the area of Furnace Creek Wash, strike slip is indicated by low-angle grooves and fault mullions, west-northwest-trending en echelon folds, north-northeast-striking normal faults, and by evidence that west-northwest-directed extension was greater on the southwest side of the fault zone than on the northeast side. Vertical movements are recorded by marginal conglomerates in each of the three formations and by northwest-trending folds with features characteristic of drag folds and forced folds. That the fault zone may penetrate deeply into the crust is suggested by the abundance of basalt flows and sills in the three formations of the basin as compared with the bordering terranes.

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