Metamorphosed Triassic and Jurassic volcanic and sedimentary rocks have been mapped, described, and measured in the Singatse, Buckskin, and northern Wassuk Ranges near Yerington, west-central Nevada. Herein, we establish new formation names for these rocks and correlate them regionally with other Triassic-Jurassic rocks, in part by use of fossil and radiometric ages. From oldest to youngest, rocks in the Singatse Range consist of a Middle Triassic or older volcanic sequence (McConnell Canyon volcanics), an Upper Triassic sequence of interbedded fine-grained clastic sedimentary rocks, carbonate rocks, tuffaceous sedimentary rocks, and tuffs (Malachite Mine Formation and tuff of Western Nevada Mine), a thick Upper Triassic limestone (Mason Valley Limestone), an uppermost Triassic and Lower Jurassic siltstone sequence (Gardnerville Formation), an Early and/or Middle Jurassic limestone-gypsum-quartzite sequence (Ludwig Mine Formation), and Middle Jurassic volcanic rocks. The sequence is exposed in septa between two Middle Jurassic batholiths and was folded and metamorphosed during emplacement of the batholiths. The Middle Jurassic volcanic rocks are best exposed in the Buckskin Range to the west, where they consist of a lower andesitic sequence (Artesia Lake volcanics) and an upper sequence of more felsic, porphyritic rocks (Fulstone Spring volcanics). The Triassic and Early Jurassic rocks are also exposed in the Wassuk Range to the east and include a thick section of andesitic and silicic volcanics, which may be in part equivalent to the McConnell Canyon volcanics, the lower part of which is intruded by the possibly cogenetic Middle Triassic Wassuk diorite and associated quartz monzonite and quartz porphyry. The McConnell Canyon volcanics apparently formed as part of an Early to early Late Triassic continental-margin volcanic arc that extended from the Mojave Desert area to northern California and Nevada. Volcanism waned in Late Triassic time, and the volcanic rocks were covered by interbedded volcaniclastic, clastic sedimentary, and carbonate rocks that include the Malachite Mine Formation and tuff of Western Nevada Mine. Late Triassic carbonate sequences, such as the Mason Valley Limestone, succeed the interbedded rocks, but this appears to have taken place earlier to the north, whereas volcanism persisted for a longer time to the south. Fine-grained siliciclastic sedi ments, with minor carbonate and local volcanic-derived strata, were deposited above the more massive carbonates in a wide area during latest Triassic and Early Jurassic deposition of the Gardnerville Formation and correlative rocks. The Ludwig Mine Formation is part of a sequence of quartz-rich sandstone, evaporates, and carbonates that is widespread in western Nevada and lies on top of and ties together diverse older rock sequences of quite different character. In addition to the arc volcanic, carbonate, and clastic sequence of Yerington and surrounding regions, these older rock sequences include thick, lithologically different, basinal turbidite-mudstone sequences of similar Late Triassic to Early Jurassic age to the north, strata of the shelf terrane to the northeast and east, and probably also rocks of the North American continental platform and parts of the Sierra Nevada. The Artesia Lake and Fulstone volcanics comprise a Middle Jurassic volcanic center related to the Yerington batholith and to nearby igneous centers that is part of a volcanic arc that extended from north of the Yerington district southward through the Mojave Desert and Arizona.

Abstract The Buckskin Range lies approximately 4 km west of the Yerington porphyry copper district and hosts the Artesia Lake and Fulstone Spring volcanic sequences that structurally overlie the Yerington batholith. Hy-drothermal alteration minerals characteristic of advanced argillic, sericitic, and marginal porphyry copper-type alteration assemblages have been detected via infrared spectrometry, X-ray diffraction, petrography, micro-probe analysis, and hand-lens based-field mapping in the central Buckskin Range. It is postulated that high-level alteration in the Artesia Lake Volcanics may be contemporaneous with the main event of sericitic alteration and pyrite deposition in the deeper porphyry copper environment. The presence of sericitic alteration underlying or overprinting hypogene advanced argillic assemblages may imply that fluids responsible for porphyry copper mineralization have ascended to epithermal depths. The spatial relationships of hydrothermal alteration in the Buckskin Range suggest an evolution of low-pH, sulfide-bearing fluids to nearly neutral, oxide-rich hydrothermal fluids. Sulfide-rich, feldspar-destructive advanced argillic and sericitic alteration is crosscut and overlain by feldspar-stable, oxide-rich sericite-hematite-chlorite alteration. Sericite-hematite-chlorite alteration is abruptly overlain by potassium-added, feldspar-stable calcite-chlorite-hematite alteration, produced by late sodic-calcic or potassium-enriched fluids possibly derived from sedimentary or evaporitic brines.

Abstract: The life cycle of a fault following initiation is governed in part by the reshear criterion, of which rock surface friction is the critical factor limiting the dip of a fault at its death. Using structural restorations where the initial and final dips of faults can be ascertained, the coefficient of rock surface friction is calculated for well-characterized extended locales ( n = 20) in the Basin and Range province, many with multiple fault generations ( n = 34). The calculated values exhibit a considerably wider range (0.19–1.33) than previously reported. The amount of tilting associated with each fault generation is compared with eight characteristics (mean slip magnitude, tilting per unit of slip, fault spacing, percentage extension, absence or presence and composition of magmatism, duration of extension, timing of extension and strain rate). No statistically strong correlation was found with any of the examined characteristics, although tentative linkages were noted with percentage extension, strain rate and mean slip magnitude from weighted regression analysis. These results are consistent with normal faults behaving as non-linear systems, with friction being an emergent property.