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Geology topics

M.L. Silberman

Publications and source records attributed to M.L. Silberman.

At least 37 records · Page 2Linked to original sources
USGS1979

Recent crustal movements in the Sierra Nevada-Walker lane region of California-Nevada: Part i, rate and style of deformation

This review of geological, seismological, geochronological and paleobotanical data is made to compare historic and geologic rates and styles of deformation of the Sierra Nevada and western Basin and Range Provinces. The main uplift of this region began about 17 m.y. ago, with slow uplift of the central Sierra Nevada summit region at rates estimated at about 0.012 mm/yr and of western Basin and Range Province at about 0.01 mm/yr. Many Mesozoic faults of the Foothills fault system were reactivated with normal slip in mid-Tertiary time and have continued to be active with slow slip rates. Sparse data indicate acceleration of rates of uplift and faulting during the Late Cenozoic. The Basin and Range faulting appears to have extended westward during this period with a reduction in width of the Sierra Nevada. The eastern boundary zone of the Sierra Nevada has an irregular en-echelon pattern of normal and right-oblique faults. The area between the Sierra Nevada and the Walker Lane is a complex zone of irregular patterns of ho??rst and graben blocks and conjugate normal-to right- and left-slip faults of NW and NE trend, respectively. The Walker Lane has at least five main strands near Walker Lake, with total right-slip separation estimated at 48 km. The NE-trending left-slip faults are much shorter than the Walker Lane fault zone and have maximum separations of no more than a few kilometers. Examples include the 1948 and 1966 fault zone northeast of Truckee, California, the Olinghouse fault (Part III) and possibly the almost 200-km-long Carson Lineament. Historic geologic evidence of faulting, seismologic evidence for focal mechanisms, geodetic measurements and strain measurements confirm continued regional uplift and tilting of the Sierra Nevada, with minor internal local faulting and deformation, smaller uplift of the western Basin and Range Province, conjugate focal mechanisms for faults of diverse orientations and types, and a NS to NE-SW compression axis (??1) and an EW to NW-SE extension axis (??3). ?? 1979.

Tectonophysics↗
USGS1979

Preliminary report on the petrography and geochemistry of basalt from the Pribilof Islands and vicinity, southern Bering Sea

Alkali basalt from the Pribilof Islands has been described by several workers (Washington and Keyes, 1930; Barth, 1956; Cox and others, 1966; and Kay, 1977). This report complements the previous reports by providing new petrographic and geochemical data for samples from St. Paul and St. George Islands and from two dredge hauls near St. George Island (Fig. 1). The geologic setting of the Pribilof Islands region is given by Barth (1956), Hopkins and Einarsson (1965), Cox and others (1966), Hopkins and others (1969), Marlow and others (1976), and Hopkins and Silberman (1978). Quaternary basalt (Table 1) (Cox and others, 1966; Hopkins, 1976; Simpson and others, 1979) is extruded onto the structurally high Pribilof Ridge (Marlow and others, 1976) which consists of rocks as old as late Jurassic (Vallier and others, 1979). Barth (1956) recognized the structural implication of alkalic volcanism in back-arc environments. We plan to interpret alkalic volcanism in the Pribilof Islands within the context of recent tectonic and petrologic findings in the southern Bering Sea. Funds for this project were provided jointly by the U.S. Geological Survey and Bureau of Land Management. Funds from the Bureau of Land Management were managed by the Outer Continental Shelf Environmental Assessment Program (OCSEAP) office of the National Oceanic and Atmospheric Administration (NOAA).

Alaska↗
USGS1978

Potassium-argon ages of basement rocks from Saint George Island, Alaska

Potassium-argon ages from basement granitic rocks that intrude serpentinized peridotite on St. George Island, Alaska, range from 50 to 57 million years, with an initial argon isochron age. interpreted as a minimum figure, of 52 ± 2 m.y. The age of the granitic rocks and their association with serpentinized peridotite near the continental margin, which apparently marks the site of a Mesozoic subduction zone, suggest that the position of the subduction zone shifted southward to the Aleutian Trench in early Tertiary time.

Alaska↗
USGS1976

Direct dating of mineralization at Goldfield, Nevada, by potassium-argon and fission-track methods

Potassium-argon dating of hypogene alunite and K-mica from hydrothermally altered rocks at Goldfield, Nevada, yields mineralization ages of 20 to 21 m.y., in good agreement with a mineralization age established by potassium-argon dating of unaltered premineralization and postmineralization volcanic units. Premineralization volcanic units that are pervasively propylitized cannot be dated by the potassium-argon method but yield zircon fission-track ages, and in several cases yield concordant apatite fission-track ages. Two samples from premineralization units yield apatite ages concordant with the age of mineralization established by potassium-argon geochronometry, reflecting annealing of the apatite during the hydrothermal episode.Potassium-argon dating of supergene alunite samples yields imprecise ages in the range 9 to 12 m.y. that probably record the first exposure of their hydrothermally altered host rocks to oxidizing conditions. Potassium-argon dating of postmineralization basalts and silicic tuffs interbedded with conglomerates bearing altered rock clasts shows that the altered area was eroded nearly to present topographic levels by 11 m.y. ago, at which time it was covered by basalt flows now represented only by scattered remnants. Apatites from premineralization volcanic units give fission-track ages of 20 m.y. or more, indicating that no significant thermal event has affected altered rocks at Goldfield since mineralization took place.

Nevada↗
USGS1976

Tectonic implications of space-time patterns of Cenozoic magmatism in the western United States

Locations of 2,100 radiometrically dated igneous rocks were plotted on a series of 20 maps, each representing an interval within the period 80 m.y. B.P. to present. Derivative maps showing the distributions in space and time of dated granitic intrusive rocks, silicic lavas and domes, ash-flow tuffs, andesitic-dacitic rocks, and basalts depict well the two main petrogenetic assemblages noted previously by others: (1) mainly intermediate andesitic-dacitic suites, including associated granitic intrusive rocks, silicic extrusive rocks, and minor basaltic lavas, are interpreted as reflecting plate interactions related to subduction along the continental margin; and (2) bimodal suites, dominantly basaltic but with minor silicic extrusive rocks, are interpreted as reflecting extensional tectonics. Space-time distribution of the two assemblages suggests that magmatic arcs extended continously parallel to the continental margin from Canada to Mexico in latest Mesozoic and in Oligocene times. An early Cenozoic null in magmatism in the Great Basin may delineate the region where subduction was arrested temporarily by development of the proto-San Andreas fault as a transform in coastal California or, alternatively, may reflect complex subsurface configurations of subducted plates. The late Cenozoic transition from subduction-related magmatism to extention-related basaltic volcanism in the southern Cordillera occurred at different times in different areas in harmony with current concepts about the migration of the Mendocino triple junction as the modern San Andreas transform fault was formed. The plots also reveal the existence of several discrete magmatic loci where igneous activity of various kinds was characteristically more intense and long-lived than elsewhere.

Earth and Planetary Science Letters↗
USGS1973

Stable isotope and chemical relations during mineralization in the Bodie mining district, Mono County, California

Stable isotope and chemical relations have been determined in a typical epithermal Au-Ag deposit located in the Bodie mining district of California. Analyses were made of altered host rocks, vein minerals, alteration clays, fluid inclusions, modern spring waters, and unaltered rocks of the area.The results indicate that a hydrothermal convection system was set up by the interaction of a cooling shallow intrusion and local meteoric water. The water traveled to depth where it picked up ore constituents and SiO 2 , K, and Rb, without significant shifts in the stable isotope ratios of the water. The altered rocks have equilibrated to various degrees with an ore fluid of constant K/Rb, O 18 /O 16 and D/H ratios. Deposition of ore took place over the approximate temperature range 215 degrees -245 degrees . From C 13 /C 12 ratios of minor calcite, a volcanic source of CO 2 is postulated. The chemical and isotope composition of the ore fluid is strikingly similar to that of modern spring waters in the area.All ore deposition at Bodie took place from essentially isotopically unaltered ground water with delta O 18 = -13ppm and delta D = -98ppm.

California↗