Geology topics

Research about Roberts Mountains

Source-linked reports with geographic coverage including Roberts Mountains.

3 recordsLinked to original sources

USGS1976

Bootstrap window, Elko and Eureka Counties, Nevada

The Bootstrap window in the Roberts Mountains thrust of north-central Nevada contains a 1,500-ft (460-m)- thick autochthonous section of carbonate assemblage rocks. These carbonate rocks include the upper part of the Roberts Mountains Formation and an unnamed limestone of Devonian age. They contain abundant material that must have been deposited in or near a reef. Allochthonous chert and shale of the siliceous assemblage, presumably Ordovician and Silurian in age, are present around the window and in a north-trending graben within the window. The Paleozoic rocks contain altered dikes, most of which may originally have been granodioritic. The localized recrystallization in the Paleozoic rocks probably occurred during dike emplacement. Sometime after the intrusion; both the dikes and their host rocks were epithermally altered. Some gold has been mined, and relatively high gold values (≥1 ppm) occur in rocks of the siliceous assemblage in and near the northern part of the steep north-trending fault zone on the west side of the graben. Areas of secondary alteration and of high values of silver and mercury are more widespread than the area of high gold values. The highest concentrations of silver and mercury, however, are also found near the same gold-bearing fault zone.

Nevada↗

USGS1974

Stratigraphic evidence on the age of the Roberts Mountains thrust, Eureka and White Pine Counties, Nevada

Several stratigraphic discontinuities in Devonian and Mississippian sedimentary sequences in folded thrust plates east of the Roberts Mountains thrust of central Nevada indicate that the thrust was sporadically active during this interval. From estimates for displacement and time involved for the thrust, the average rate of movement was 1 cm/5 yr, which is comparable to current concepts of the rate of orogenic movements. A further extrapolation of this rate to the longer period during which orogenies have been recognized in the Great Basin suggests total horizontal shortening of 400 to 500 mi (640-800 km).

Nevada↗

USGS1942

Reconnaissance survey of the Roberts Mountains, Nevada

The Roberts Mountains region, central Nevada, provides an excellent section of Paleozoic rocks ranging from Upper Cambrian to Permian. Major low-angle thrusting is indicated by deformed Ordovician strata resting on Paleozoics of varying age. Overlying a thick breccia zone, the upper thrust plate consists of sandstones, andesitic flows and tuffs, black shales, and bedded cherts (Vinini formation). Ordovician age of the Vinini is established on the basis of graptolite faunules. A belt of Lower to Middle Ordovician graptolitic facies similar to the Vinini formation crosses the Great Basin west of Roberts Mountains. Deposits of roughly the same age in the Roberts Mountains meridian and eastward are dominantly limestone, carrying distinct faunas. Axial planes of overturned folds in the thrust plate dip west, a further indication that the upper thrust plate moved from west to east. Minimum horizontal displacement is 16 miles. The date of thrusting is uncertain, but presumably was later Cretaceous or early Tertiary. Following thrusting, an alaskite stock and rhyolite porphyry plugs were intruded; lava flows and tuffs covered the area in part. Thrust plate and cover of volcanics have been broken into normal fault blocks. The post-thrusting igneous rocks, like volcanic rocks of Utah and New Mexico, are characterized by high potash content.

Nevada↗