Award Date


Degree Type


Degree Name

Master of Science in Geoscience



First Committee Member

Wanda J. Taylor, Chair

Second Committee Member

Rodney V. Metcalf

Third Committee Member

Margaret N. Rees

Graduate Faculty Representative

Stanley D. Cloud

Number of Pages



In the northern Hiko Range, extension occurred in four temporally distinct episodes during the Cenozoic. The extensional events are (1) prevolcanic (> 27.31 ± 0. 03 Ma), (2) syn-volcanic (between 22.78 ± 0,03 and 18.5 ± 0.4 Ma), (3) Tertiary(?) post-volcanic ( < 14.7 ± 0.4 Ma), and ( 4) Pliocene(?) - Quaternary. Four fault sets are delineated based on orientation and cross-cutting relationships: (I) northeast- to northwest-striking moderately dipping prevolcanic faults, (2) east-west striking, steeply-dipping syn-volcanic faults, (3) east-west- and east-northeast-striking, steeply dipping Tertiary(?) post-volcanic faults, and (4) generally north-striking steeply dipping Pliocene (?) - Quaternary faults.

Prevolcanic faults in the northern Hiko Range are interpreted to be footwall faults to an Oligocene age extensional system. These faults increase the area affected by Oligocene extension and support existing evidence that suggests this event is widespread.

A tectonomagmatic rift model has been proposed to explain synvolcanic extension during the Tertiary in the northern Basin and Range province. This model suggests that the mechanism for change in the horizontal principal stress direction, from north-south oriented o2 and east-west oriented o3 to east-west oriented o1 and north-south oriented o3, is temporally and spatially associated with the southward passage of a belt of volcanism. A few east-west-striking synvolcanic faults crop out in the Hiko Range and can be explained by a tectonomagmatic rift model. However, the majority of the faults are postvolcanic and are not readily explained by the tectonomagmatic rift model. Both eastwest- and east-northeast-striking oblique-slip faults occur along the Timpahute lineament. These faults are postvolcanic, but should be synvolcanic if the tectonomagmatic rift model applies. In addition, faults in the central part of the Timpahute lineament were active more than once since the Oligocene and the lineament may be related to transform and transverse faults formed during Precambrian rifting.

The Hiko fault zone is a segmented fault of Pliocene (?) - Quaternary age that may still be active and is interpreted to be the bounding fault of a half graben in Pahranagat Valley. A leaky segment boundary, the Hiko segment boundary (named here), is a structural boundary interpreted to be breached by faulting along the Hiko fault zone. Segment boundaries are sites where earthquakes begin or end. Earthquakes associated with the Hiko segment boundary, segments of the Hiko fault zone, and potentially active faults in the Timpahute lineament, pose seismic hazards, such as liquefaction, ground shaking, surface rupture, and rock falls, to the community of Hiko, Nevada.

The geology and the multiple generations of extensional structures exposed at the surface in the northern Hiko Range are similar to that in many of the oil fields in central Nevada. Therefore, this study may help understand complex trapping mechanisms, and thus, aid hydrocarbon exploration.


Cenozoic Geologic Period; Fault zones; Nevada – Hiko Mountains; Rifts (Geology); Volcanism


Geology | Tectonics and Structure | Volcanology




Best copy available