Lower Mesozoic sedimentary and volcanic rocks of the Yerington region, Nevada, and their regional context
Published:July 01, 2008
John M Proffett, John H Dilles, 2008. "Lower Mesozoic sedimentary and volcanic rocks of the Yerington region, Nevada, and their regional context", Ophiolites, Arcs, and Batholiths: A Tribute to Cliff Hopson, James E. Wright, John W. Shervais
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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.