Introduction Evaluation Prospects










Low-Angle Normal Fault Domain

The Low-Angle Normal Fault Domain encloses ranges and basins characterized by imbricate low-angle extensional faults that place younger-over-older rocks with the elimination or attenuation of variable amounts of stratigraphic section. Along with low-angle normal faults, this domain is segmented by intense high-angle faulting of variable orientation and displacement. These high-angle faults both cut and are cut by low-angle normal faults suggesting at least two periods of extensional deformation. The Low-angle Normal Fault Domain also exposes regionally metamorphosed Precambrian and Paleozoic rocks both in small patches, and across broad core complex areas.

The Low-Angle Normal Fault Domain is well displayed across a broad eastern portion of the evaluation area east of a line which marks the easternmost limit of Golconda and Roberts Mountains thrusting. This domain is adjacent to the Large-Scale Fold and Simple Fault Block Domains with a boundary formed in large part by lateral faults and lineaments such as the Warm Springs and Independence-Pequop Lineaments, and lateral faults in the southern Cherry Creek Range. These lateral faults and lineaments are separating regions that exhibit large changes in the amount and intensity of extension.

Major Low-angle normal faults are present within the following ranges with an estimate of the amount of stratigraphic attenuation in feet where known: the Ruby Mountains (7,500-9,000), East Humboldt (7,500-9,000) and Pequop (2,500-10,700) Ranges, Wood Hills (9,000) Toana-Goshute (1,200-4,500), southern Pilot (2,000), Antelope (6,500), and southern Deep Creek (1,000-3,500) Ranges, Kern Mountains (500-1,500), southern Cherry Creek (500-1,000), Schell Creek (1,000-11,000), Snake (500-8,000), Bristol (4,500-13,000) Egan (1,000-16,500), Grant (1,400-4,300), Quinn Canyon (2,000), White Pine (1,000-8,000), Horse (1,500-4,400), and Reveille (500-1,000) Ranges. The regionally metamorphosed rocks are exposed within core complexes in the Snake, Grant, Ruby, and East Humboldt Ranges, as well as discontinuous patches of greenschist to amphibolite facies in the Wood Hills, northern Pequop and Toana Ranges, Northern Egan-southern Cherry Creek, Schell Creek, southern Deep Creek and Pilot Ranges.

The geometry and estimated attenuation along most of the major low-angle faults are described within the range structure portion of this volume and are summarized here. It is important to realize that these low-angle normal faults form in complexes of multiple faults that merge with or cut one another, and exhibit upper plates with numerous, imbricate high-angle listric normal faults with small to relatively large displacements and brecciation. In the metamorphic core complex areas, low-angle detachment faults are present which separate ductily deformed and metamorphosed lower plate rocks from brittlely deformed and unmetamorphosed upper plate rocks.

The low-angle faults have variable positions in the stratigraphic section within Cambrian through Permian units. Over broad areas however, prospective source sections such as the Pilot and Chainman Formations, and potential Ordovician through Mississippian reservoir sections such as the Laketown Dolomite, and Guilmette, Simonson, and Sevy Formations have been thinned or structurally eliminated. Potential hydrocarbon traps are also severely affected, although possible trap types related to low-angle extension can also be created as discussed in the last section of this volume on potential trap types.

The estimated attenuations listed above point out some significant variation within this domain. The southern Pilot, southern Deep Creek, Reveille, and southern Cherry Creek Ranges, Kern Mountains, and portions of the Toana and Egan Ranges have relatively less low-angle attenuation and deformation than surrounding ranges. It is also generally true that the amount of attenuation and intensity of low-angle faulting generally decreases to the southwest within this domain.

Several blocks within the Low-angle Normal Fault Domain mainly expose high-angle normal faults of variable trend and displacement with few or no obvious exposures of low-angle faults. These include parts of the southern Leppy Range, Red Hills, southern Snake Range, central Schell Creek Range, central Egan Range, Spruce Mountain Ridge, northernmost Pequop Mountains, northern White Pine Range, Quinn Canyon Range, and southern Ruby Mountains. Simple Fault Block Domain.

The Simple Fault Block Domain is characterized by relatively large high-angle listric and planar normal fault blocks that do not expose internal low-angle normal or thrust faults. These blocks are cut by relatively few internal high-angle faults that are dominantly long and continuous. This domain is exposed in the southern and southeastern portion of the evaluation area and includes the Wilson Creek Range, White Rock Mountains, Limestone Hills, Fairview, southern Schell Creek, southern Egan, Fortification, Golden Gate and Seaman Ranges, and the southern Pancake Range to the west.

The relatively simple fault blocks within this domain do show varying degrees of internal segmentation by high-angle normal faults, as well as various levels of stratigraphic exposure. The most intact blocks are present in the southern Egan, Schell Creek, and Fairview Ranges and the Limestone Hills. These blocks expose Cambrian through Tertiary rocks which are cut by only a handful of high-angle faults, and locally show gentle folding of the Paleozoic units.

The Wilson Creek, Seaman, Golden Gate, and southern Pancake Ranges, and the White Rock Mountains dominantly expose Tertiary rocks and local Upper Paleozoic units that are cut by more numerous high-angle faults of variable orientation, continuity, and displacement. Still, the blocks in these ranges are relatively simple and intact compared to other areas, particularly within the Low-Angle Normal Fault Domain which surrounds most of the Simple Fault Block Domain. The southern Pancake Range between Black Rock Summit and Portuguese Mountain is the most segmented block in this domain. Even this range is a large east dipping homoclinal block of Ordovician through Mississippian sediments cut by numerous short, small to moderate displacement high-angle fault segments.

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Last modified: 09/12/06