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Geology topics

R. L. Smith

Publications and source records attributed to R. L. Smith.

33 records · Page 2Linked to original sources
USGS1990

Petrogenetic evolution of the torfajökull volcanic complex, Iceland I. relationship between the magma types

The Torfajökull volcano, Iceland's largest silicic centre, is situated close to the junction of the active, southerly propagating Eastern Rift Zone and the South Eastern Zone, an older crustal segment. This paper provides major, trace, and some Sr isotope data on postglacial (<10000 y) rocks, i.e., tholeiitic magmas of the Eastern Rift Zone and transitional basalts, icelandites, and rhyolites of the Torfajökull centre, and assesses the relationships between the magma types in terms of the development of the Icelandic crust.Tholeiitic magmas from the Eastern Rift Zone are LILE-enriched relative to MORB. They have undergone extensive olivine-plagioclase-clinopyroxene fractionation at low pressures. Compared with the tholeiites, Torfajökull transitional basalts show LILE/HFS enrichment and higher ( 87 Sr/ 86 Sr) 1 ratios. They define several magmatic lineages and have equilibrated over a wide range of pressures. Both basalt types were derived by very small degrees of partial melting of compositionally similar mantle sources, the main difference being that the tholeiites were generated in the spinel Iherzolite, and the transitional basalts in the garnet lherzolite, stability fields, a conclusion previously reached by Meyer et al. (1985). The mantle sources may have contained LILE-enriched streaks.Low-pressure differentiation of Torfajökull transitional basalt produced an iceiandite to sub-alkaline rhyolite sequence by crystal fractionation, the rhyolites representing >90% crystallization of parental basalts. The rhyolites were emplaced as nine separate lava fields, formed during 11 eruptive episodes. The compositional range within each field is limited, and, although similar, the ranges define several magmatic lineages. Continued fractionation of plagioclase-alkali feldspar-clinopyroxene-magnetite-apatite-zircon assemblages generated peralkaline rhyolites in certain post-glacial eruptions. Chemical variations in the deposits from the Hrafntinnusker peralkaline eruption were related predominantly to alkali feldspar fractionation, and the melts were erupted from a zoned magma chamber. All postglacial volcanic rocks at Torfajokull have been mantle derived and thus represent new additions to the Icelandic crust. © 1990 Oxford University Press.

Journal of Petrology↗
USGS1988

Denitrification in a sand and gravel aquifer

Denitrification was assayed by the acetylene blockage technique in slurried core material obtained from a freshwater sand and gravel aquifer. The aquifer, which has been contaminated with treated sewage for more than 50 years, had a contaminant plume greater than 3.5-km long. Near the contaminant source, groundwater nitrate concentrations were greater than 1 mM, whereas 0.25 km downgradient the central portion of the contaminant plume was anoxic and contained no detectable nitrate. Samples were obtained along the longitudinal axis of the plume (0 to 0.25 km) at several depths from four sites. Denitrification was evident at in situ nitrate concentrations at all sites tested; rates ranged from 2.3 to 260 pmol of N 2 O produced (g of wet sediment) −1 h −1 . Rates were highest nearest the contaminant source and decreased with increasing distance downgradient. Denitrification was the predominant nitrate-reducing activity; no evidence was found for nitrate reduction to ammonium at any site. Denitrifying activity was carbon limited and not nitrate limited, except when the ambient nitrate level was less than the detection limit, in which case, even when amended with high concentrations of glucose and nitrate, the capacity to denitrify on a short-term basis was lacking. These results demonstrate that denitrification can occur in groundwater systems and, thereby, serve as a mechanism for nitrate removal from groundwater.

Massachusetts↗
USGS1988

Microbial and biogeochernical processes Soda Lake, Nevada

Meromictic, alkaline lakes represent modern-day analogues of lacustrine source rock depositional environments. In order to further our understanding of how these lakes function in terms of limnological and biogeochemical processes, we have conducted an interdisciplinary study of Big Soda Lake. Annual mixolimnion productivity (ca. 500 g m -2 ) is dominated by a winter diatom bloom (60% of annual) caused by upward transport of ammonia to the epilimnion. The remainder of productivity is attributable to chemoautotrophs (30%) and photosynthetic bacteria (10%) present at the oxic -anoxic interface from May to November. Studies of bacterial heterotrophy and particulate fluxes in the water column indicate that about 90% of annual productivity is remineralized in the mixolimnion, primarily by fermentative bacteria. However, high rates of sulphate reduction (9-29 mmol m -2 yr -1 ) occur in the monimolimnion waters, which could remineralize most (if not all) of the primary productivity. This discrepancy has not as yet been fully explained. Low rates of methanogenesis also occur in the monimolimnion waters and sediments. Most of the methane is consumed by anaerobic methane oxidation occurring in the monimolimnion water column. Other bacterial processes occurring in the lake are also discussed. Preliminary studies have been made on the organic geochemistry of the monimolimnion sediments. Carbon-14-dating indicates a lower depositional rate prior to meromixis and a downcore enrichment in 13 C of organic carbon and chlorophyll derivatives. Hydrous pyrolysis experiments indicate that the sediment organic matter is almost entirely derived from the water column with little or no contribution from terrestrial sources. The significance of the organics released by hydrous pyrolysis is discussed.

Book chapter↗
USGS1985

Isolation of anaerobic oxalate-degrading bacteria from freshwater lake sediments

Enrichment cultures that anaerobically degraded oxalate were obtained from lake sediment inocula. From these, 5 pure cultures of anaerobic oxalate-degrading bacteria were isolated and partially characterized. The isolates were Gram-negative, non-sporeforming, non-motile, obligate anaerobes. Oxalate was required for growth and was stoichiometrically converted to formate; 14 CO 2 was also recovered when 14 C-oxalate was added. Maximal growth occurred when the oxalate concentration was 50 mM. Acetate stimulated growth in the presence of oxalate, however, 14 C-experiments indicated that acetate was only utilized for cell carbon. The isolates were either spiral-shaped or rod-shaped organisms. The first morphotype grew much more slowly than the second and exhibited 13-fold lower cell yields. These isolates represent a new strain of oxalate-degrading bacteria. The second morphotype was similar to the anaerobic oxalate-degrading bacteria previously found in rumen. This report extends the known habitats in which anaerobic oxalate-degrading organisms have been found to include aquatic sediments.

Archives of Microbiology↗
USGS1982

Progress report on lithium-related geologic investigations in Bolivia

The September 1, 1981, Samoa Islands Region earthquake occurred at the extreme northern end of the Tonga arc in a region where the Pacific plate may be disjointed along a hinge fault. In the last 50 years, magnitude 7 or greater earthquakes have occurred in this region on the average of once every six years, but four 7+ events have now occurred within the last six years. The mainshock was preceded about two hours earlier by a foreshock that was used as a calibration event for the Joint Epicenter Determination relocation of the mainshock and nearby seismicity occurring within a period seven months prior to and one week after the mainshock. The foreshock, better-located events of the prior seismicity, and most aftershocks are concentrated in a group near the mainshock epicenter, but several more distant aftershocks suggest that the aftershock zone may have been as large as 125 km in length and trended about S35?E. Identification of depth phases from a full suite of broadband records gives source depths of 25-3km for the mainshock and 29.5?3 km for the foreshock using a JB earth model. Source parameters were determined for the mainshock utilizing WWSSN analog and GDSN digital data. The preferred fault plane solution based on P-wave first motion data is a south by southwesterly steeply dipping normal fault, remarkably similar to the mechanism reported by Johnson and Molnar (1972) for the nearby earthquake of April 20, 196B. A waveform inversion technique described by Sipkin (1982), when applied to long-period P waveforms, gives an 'average' point source solution for a purely deviatoric moment rate tensor at a preferred source depth of 22 km. Very similar results were obtained from long-period GDSN body-wave and mantle-wave data using a centroid-moment tensor inversion technique described in Dziewonski, and others (1981). Both techniques provide solutions very close to a double couple source with a south by southwesterly shallow-dipping normal fault mechanism. To obtain the scalar mantle wave moment, GDSN vertical and transverse records 20,000 see in length were processed as described by Buland and Taggart (1981). Averaging all the data from Rayleigh and Love waves yields an estimate of 3.8 x 10^27 dyne-cm (as compared to about 1.9 x 10^27 from body-wave moment tensor inversions) or a moment magnitude (Mr) of 7.6. For the portion of the waveform analysed (50-5B sec), the body-wave inversion performed by Sipkin gives a source time function of duration approximately 28 sec with two peaks in activity. Simultaneous analysis of short-period records, and broadband ground displacements and velocities, a method described by Harvey and Choy (1982) and Choy and Boatwright (1981) revealed a complex rupture consisting of two subevents, of about the same moment, separated in time by about 25 sec, and with durations of about 25 sec each. The two peaks in activity resolved by the body-wave moment tensor inversion correspond to the first of these subevents.

Open-File Report↗
USGS1960

Zones and zonal variations in welded ash flows

Welded tuffs are recognized as special parts of ash flows, other pyroclastic flows, or, more rarely, air-fall deposits. Ash flows may be emplaced at any temperature below a maximum eruption temperature. Those emplaced above a minimum welding temperature may show any and all degrees of welding and crystallization.

Professional Paper↗
USGS1958

The deuterium content of water in some volcanic glasses

The deuterium-hydrogen composition (relative to Lake Michigan water = 0.0) of water extractsd from coexisting perlite and obsidian from eleven different localities was determined. The water content of the obsidians is generally from 0.09 to 0.29 per cent by weight, though two samples from near Olancha, California, contain about 0.92 per cent. The relative deuterium concentration is from −4.6 to −12.3 per cent. The coexisting perlite contains from 2.0 to 3.8 per cent of water with a relative deuterium concentration of −3.1 to −16.6 per cent. The deuterium concentration in the perlites is not related to that in the enclosed obsidian. The deuterium concentration in the perlite water is related to the deuterium concentration of the modern meteoric water and the perlite water contains approximately 4 per cent less deuterium than does the groundwater of the area in which the perlites occur. The above relations hold true for perlites from northern New Mexico, east slope of the Sierra Nevada. California Coast Range, Yellowstone Park, Wyoming, and New Zealand. As the water in the obsidian is unrelated to meteoric water, but the enclosing perlite water is related, we believe that this is evidence for the secondary hydration of obsidian to form high water content perlitic glass.

Geochimica et Cosmochimica Acta↗