Cenozoic Volcanism and Sedimentation, Silver Peak Region, Western Nevada and Adjacent California

Abstract

Cenozoic deposits of the Silver Peak region, western Nevada, and adjacent California consist principally of continental sedimentary and pyroclastic rocks of the Esmeralda Formation and lavas and tuffs of the Silver Peak volcanic center.The sedimentary rocks comprise several thick sequences of tuffaceous volcanic sandstone and siltstone and interbedded air-fall tuff. These rocks were deposited in basins that coincide in a general way with the present valleys. Thick wedges of conglomerate and sandstone occur along the basin margins and reflect source areas.Most of the sedimentary rocks were deposited under fluctuating fluviatile and lacustrine conditions, but paludal conditions prevailed locally. Abrupt facies changes and numerous local unconformities indicate that deposition was not uniform within a given basin.The sedimentary rocks range in age from late Miocene to late Pliocene. The oldest reliably dated rocks in the Esmeralda Formation are 13.1 m.y. 577 on June 26, 2015 memoirs.gsapubs.org Downloaded from 578 STUDIES IN VOLCANOLOGY by K-Ar (Barstovian), and all sedimentary strata are younger than an ashflow sheet dated at 21.5 m.y. by K-Ar. An air-fall tuff in the upper part of the section has a K-Ar age of 4.3 m.y.Rocks of the Silver Peak volcanic center, 4.8 to 6.1 m.y. by K-Ar, crop out principally in the central part of the Silver Peak Range. Along the margins of the range, they overlie and interfinger with the various sedimentary sequences. The volcanic rocks are mostly rhyolite and trachyandesite tuffs and flows with subordinate basalts and andesites.Basin and Range faulting began in late early to middle Miocene time and has continued intermittently to the present, but present topography was largely established by late Pliocene time. CONTENTS

Anisotropy of magnetic susceptibility data bearing on the transport direction of mid-tertiary regional ignimbrites, Candelaria Hills area, West-Central Nevada

“…To the east, the regional ignimbrites may extend to the edge of the Big Smokey Valley, but no conclusively identified exposures of the three regional ignimbrites have been reported east of the Silver Peak Range and there are no mapped occurrences or published correlations of the ignimbrites east of the Candelaria Hills. Because of the regional distribution of the sequence, most studies have focused only on local sections in specific areas (Page 1959;Ross 1961;Robinson et al 1968Robinson et al , 1976Crowder et al 1973;Robinson and Crowder 1973;Stewart et al 1975;Stewart 1979Stewart , 1981aGarside 1979;Speed and Cogbill 1979a, b, c;Robinson and Stewart 1984). Rather than attempting to reconcile earlier conventions, we maintain the convention proposed by Robinson and Stewart (1984).…”

Mineral resources of the Silver Peak Range Wilderness Study Area, Esmeralda County, Nevada

“…None of the caldera structure is evident and the caldera boundaries (Robinson and others, 1976;Stewart and others, 1974) were presumably drawn on the basis of thickness and location of lavas in and near the caldera (Robinson, 1968;Robinson, 1972Robinson, , p. 1696 Faulting in the study area consists almost entirely of northeast-trending high-angle normal faults (pi. 1).…”

“…According to Robinson (1968), the caldera was formed after the emplacement of the rhyolite of Cottonwood Spring, which would make its age about 6 Ma.…”

Thermal Relaxation of a Magmatic Arc Complex, Mount Barcroft Area, Eastern California:40Ar/39Ar Geochronologic Study of Hornblende and Biotite from Igneous and Metamorphic Rocks

“…Other, relatively fresher diabasic rocks display zoned igneous plagioclase laths, relict augite, and are feebly recrystallized or are virtually unmetamorphosed; most of these are probably Cenozoic in age. Because the unmetamorphosed mafic dikes, as well as the metadiabases, contain small amounts of interstitial quartz (hypersthene normative), they are not correlative with fresh, 4-8 Ma olivine-rich alkali basalt tableland flows (Robinson et al, 1968) that are present along the east side of the study area.…”