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James L. Bischoff

Publications and source records attributed to James L. Bischoff.

At least 55 records · Page 3Linked to original sources
USGS1988

Liquid-vapor relations in the critical region of the system NaCl-H 2 O from 380 to 415°C: A refined determination of the critical point and two-phase boundary of seawater

Pressure-temperature-composition ( P - T - x ) relations for coexisting vapor and liquid phases in the system NaCl-H 2 O were determined experimentally in the critical region from 380 to 415°C. The results provide much improved control on the P - T - x critical line in this region. The critical point of seawater (3.2 wt% NaCl solution), which is bracketed in the present study, is at 407°C and 298.5 bar. In addition, the P - T two-phase boundary of seawater was re-determined. These results provide increased precision and accuracy for theoretical models of critical phenomena in this important two-component system and of the limiting P - T conditions of seawater in seafloor geothermal systems.

Geochimica et Cosmochimica Acta↗
USGS1988

The laboratory albitization of mid-ocean ridge basalt

Complete alteration of fresh mid-ocean ridge basalt to albite + actinolite + smectite took place in the presence of quartz and 3.4m NaCl at 350°C and 400 bars. Significant Na-metasomatism occurred in exchange for Ca + Fe + Mn. In contrast, alteration of the basalt/quartz mixture with a synthetically prepared "natural brine," and basalt with 3.4m NaCl or "natural brine" did not produce significant albitization. Based on these and previous experiments that reacted basalt with a variety of fluids, it is concluded that excess silica, a high Na/Ca ratio, and an absence of strong acidity (dissolved Mg) in the altering fluid are important for the albitization of basalt.

Journal of Geology↗
USGS1987

Critical behavior of dilute NaCl in H2O

The compositions of the saturated vapor and liquid phases are measured for the system NaCl-H 2 O at 380°C, which is close to the critical point of pure water. The shape of the phase equilibrium curve is classical, which confirms a conclusion reached earlier on the basis of less accurate data. This implies that the long-range forces introduced by the NaCl suppress the non-classical effects present in pure H 2 O. An empirical equation of a classical type fits these data.

Chemical Physics Letters↗
USGS1987

Pressure-composition relations for coexisting gases and liquids and the critical points in the system NaCl-H 2 O at 450, 475, and 500°C

Pressure-temperature-composition ( P , T , x ) relations for the co-existing vapor and liquid phases in the system NaCl-H 2 O were determined experimentally at 450, 475, and 500°C. Data for each isotherm include P - x relations near the critical point and extend to the three-phase assemblage vapor-liquid-halite on the vapor side. On the liquid side the P - x data range from the critical point to the room-temperature halite saturation point (~25 wt.% NaCl). Critical pressures were calculated from measured pressures and compositions and classical theory. The results generally support the few data points of Urusova (1974, 1975) and Ölander and Liander (1950) but differ markedly from the extensive data of Sourirajan and Kennedy (1962).

Geochimica et Cosmochimica Acta↗
USGS1987

Phase separation in seafloor geothermal systems: An experimental study of the effects on metal transport

Experimental investigations were carried out by reacting natural and evolved sea-water with crystalline basalt from the Juan de Fuca Ridge in order to study the effects of vapour-liquid phase separation on metal mobilization in sea-floor geothermal systems in which phase separation occurs between the top of a magma chamber (300-500 bar) and the sea-floor (230-250 bar). The geochemical processes produced by a combination of closed-system phase separation and adiabatic expansion under the conditions characterizing the sea-floor geothermal systems resulted in a significant increase in the acidity and concentration of heavy metals in the liquid phase and strikingly high concentrations of metals in the vapour.

American Journal of Science↗
USGS1986

The system NaCl-H 2 O: relations of vapor-liquid near the critical temperature of water and of vapor-liquid-halite from 300° to 500°C

Vapor-liquid relations ( P - T - x ) for the system NaCl-H 2 O were determined experimentally at temperatures spanning the critical temperature of water ( T c ), the lowest temperature in the system at which critical behavior occurs. In addition, vapor-liquid-halite P - T - x (vapor) relations were determined from 300° to 500°C. Results show that at 373.0°C, immediately below T c , the vapor side of the isothermal vaporliquid P-x boundary has a shape quite different from that previously conceived. The NaCl content of the vapor increases with pressure in a smooth manner from the pressure of the three-phase assemblage (135 bars, 0.0029% NaCl), to a pressure just below that of the vapor pressure of pure water (0.012% NaCl at 184 bars). Above this pressure the boundary abruptly reverses and projects asymptotically to 0% NaCl in a beak-like shape at 218 bars, the vapor pressure of pure water. At 375.5°, slightly above T c , the asymptote disappears, and is replaced by a rounded nose. At progressively higher temperatures, the nose disappears and by 380°C the familiar symmetrical bell-shaped curve predominates with the critical point defined by the top of the bell. The P - T curve of the three-phase assemblage determined in the present study is in agreement with previous workers. The NaCl content of the three-phase vapor, however, is much higher than some literature values at temperatures above 410°C.

Geochimica et Cosmochimica Acta↗
USGS1985

Uranium-series dating of sediments from Searles Lake: Differences between continental and marine climate records

One of the major unresolved questions in Pleistocene paleoclimatology has been whether continental climatic transitions are consistent with the glacial δ 18 O marine record. Searles Lake in California, now a dry salt pan, is underlain by sediment layers deposited in a succession of lakes whose levels and salinities have fluctuated in response to changes in climate over the last 3 × 10 6 years. Uranium-series dates on the salt beds range from 35 × 10 3 to 231 × 10 3 years. This range of dates allows identification of lake-sediment horizons that are time correlatives of the boundaries of marine isotope stages from the recent 3/4 boundary back to the 8/9 boundary. The 5/6 boundary coincided with a deepening of the lake, but the analogous 1/2 boundary coincided with desiccation. The 3/4, 4/5, 6/7, 7/8, and 8/9 boundaries correspond in age to horizons that record little or no change in sedimentation or climate. These hydrologic results demonstrate that the continental paleoclimate record at this mid-latitude site does not mimic the marine record.

California↗
USGS1984

The critical point and two-phase boundary of seawater, 200–500°C

The two-phase boundary of seawater was determined by isothermal decompression of fully condensed seawater in the range of 200–500°C. The pressure at which phase separation occurred for each isotherm was determined by a comparison of the refractive index of fluid removed from the top and bottom of the reaction vessel. The critical point was determined to be in the range of 403–406°C, 285–302 bar and was located by the inflection in the two-phase boundary and by the relative volume of fluid and vapor as a function of temperature. The two-phase boundary of 3.2% NaCl solution was found to coincide exactly with that of seawater over the range tested in the present study. The boundary for both is described by a single seventh-order polynomial equation. The two-phase boundary defines the maximum temperature of seawater circulating at depth in the oceanic crust. Thus the boundary puts a limit of about 390°C for seawater circulating near the seafloor at active ocean ridges (2.5 km water depth), and about 465°C at the top of a magma chamber occurring at 2 km below the seafloor.

Earth and Planetary Science Letters↗
USGS1983

Uptake and transport of heavy metals by heated seawater: A summary of the experimental results

In general, the chemistry of seawater experimentally reacted with basalt is in accord with the observed chemistry of the 350°C vent waters from 21°N on the East Pacific Rise. Experiments at 350°C, 500 bar, and a water/rock ratio of ≤10 reproduce most of the major components in the vent waters, in particular the low Mg and SO 4 and high Si0 2 , Ca, and K. In comparison with the vent waters however the experimental fluids are deficient in H + and heavy metals. Experiments with natural and evolved seawater (Mg and SO 4 depleted) at ≥400 C and 500 bars or 375°C and ~375 bars under rock-dominated conditions more closely reproduce the vent-water chemistry.

Book chapter↗
USGS1983

A note on the chemistry of seawater in the range 350°-500°C

The chemistry of seawater at conditions of 350° to 500°C, 220 to 1000 bars (22 to 100 MPa) is controlled by reactions involving magnesium hydroxide sulfate (MHSH) and anhydrite. During progressive heating from 350° to 500°C at 1000 bars (100 MPa), MHSH with a ratio of 1.25 is formed via precipitation from solution and via reaction of solution with pre-existing anhydrite. During adiabatic expansion the MHSH extracts additional SO 4 from seawater and converts to a stoichiometry in which . These reactions control and greatly change the concentrations of Ca, Mg, SO 4 in solution and produce significant ionizable hydrogen, attaining 11.7 mmoles kg −1 at maximum conditions.

Geochimica et Cosmochimica Acta↗
USGS1983

Geochemistry and economic potential of massive sulfide deposits from the eastern Pacific Ocean

Bulk chemical analyses are performed for major and minor elements using a variety of techniques on a suite of 9 samples of sea floor massive sulfide deposits from 21?N EPR, Juan de Fuca Ridge and Galapagos Rift. Results indicate that deposits at 21?N and Juan de Fuca are very similar despite a geographic separation of 2300 km and are composed primarily of Zn, Fe, and S, with important minor concentrations of Ag, As, Cd and Ge. The Galapagos Rift massive sulfide is primarily Fe, Cu and S and with important minor contents of only Co and Mo. Au is low, ranging from below detection up to 0.17 ppm. Pt group metals are very low, and average about 0.001 ppm. Consideration of enrichment factors and relative metal abundance suggests that MORB is a sufficient source for all the metals enriched in the sea floor deposits. The economically important metals for the 21?N and Juan de Fuca deposits are primarily Zn and Ag, (97%) with potential by-products of Cu, Cd and possibly, Ge. For the Galapagos Rift, the primary value is with Cu (86%) with potential by-products of Co and Mo. The Galapagos Rift deposit is similar to, but contains about twice the Cu content, of typical ore from the Skouriotisa mine of the Troodos complex of Cyprus. The grade of the 21?N/Juan de Fuca deposits is 4 times greater than that of the Galapagos Rift and about twice that of prime deep-sea manganese nodules.

Open-File Report↗
USGS1982

The solubility of quartz in aqueous sodium chloride solution at 350°C and 180 to 500 bars

The solubility of quartz in 2, 3, and 4 molal NaCl was measured at 350°C and pressures ranging from 180 to 500 bars. The molal solubility in each of the salt solutions is greater than that in pure water throughout the measured pressure range, with the ratio of solubility in NaCl solution to solubility in pure water decreasing as pressure is increased. The measured solubilities are significantly higher than solubilities calculated using a simple model in which the water activity in NaCl solutions decreases either in proportion to decreasing vapor pressure of the solution as salinity is increased or in proportion to decreasing mole fraction of water in the solvent.

Geochimica et Cosmochimica Acta↗
USGS1981

Seawater sulfate reduction and sulfur isotope fractionation in basaltic systems: interaction of seawater with fayalite and magnetite at 200–350°C

Sulfate reduction during seawater reaction with fayalite and with magnetite was rapid at 350°C, producing equilibrium assemblages of talc-pyrite-hematite-magnetite at low water/rock ratios and talc-pyrite-hematite-anhydrite at higher water/rock ratios. At 250°C, seawater reacting with fayalite produced detectable amounts of dissolved H 2 S, but extent of reaction of solid phases was minor after 150 days. At 200°C, dissolved H 2 S was not detected, even after 219 days, but mass balance calculations suggest a small amount of pyrite may have formed. Reaction stoichiometry indicates that sulfate reduction requires large amounts of H + , which, in subseafloor hydrothermal systems is provided by Mg metasomatism. Seawater contains sufficient Mg to supply all the H + necessary for quantitative reduction of seawater sulfate. Systematics of sulfur isotopes in the 250 and 350°C experiments indicate that isotopic equilibrium is reached, and can be modeled as a Rayleigh distillation process. Isotopic composition of hydrothermally produced H 2 S in natural systems is strongly dependent upon the seawater/basalt ratio in the geothermal system, which controls the relative sulfide contributions from the two important sulfur sources, seawater sulfate and sulfide phases in basalt. Anhydrite precipitation during geothermal heating severely limits sulfate ingress into high temperature interaction zones. Quantitative sulfate reduction can thus be accomplished without producing strongly oxidized rocks and resultant sulfide sulfur isotope values represent a mixture of seawater and basaltic sulfur.

Geochimica et Cosmochimica Acta↗
USGS1981

Uranium-series and soil-geomorphic dating of the Calico archaeological site, California

Lithic specimens identified as artifacts have been recovered from near the base of the Yermo fan deposits at Calico, California. The soil on the fan surface is a strongly developed relict paleosol. Comparison of this soil with dated paleosols elsewhere in the southwestern United States suggests that the surface is about 80,000 to 125,000 yr old. Clasts near the base of the deposit are well cemented by laminated CaCO 3 that probably formed from groundwater action while the fan was still active. Uranium-thorium assays on the CaCO 3 indicate an age of 200,000 yr.

California↗
USGS1981

Tectonic elements of the southern part of the Gulf of California

Closely spaced seismic and bathymetric surveys in the southern province of the Gulf of California reveal a tectonically active and structurally complex plate boundary. While heat-flow measurements, seismicity, large sediment accumulations on continental margins, and the presence of oceanic crust in deep basins strongly suggest divergent plate motion, magnetic anomaly patterns are conspicuously absent in the Gulf as a whole. The rate of sediment accumulation (range: 6-1,000 m/m.y.), however, provides an alternative for the differentiation of two types of fault traces and suggests a process by which recently formed plate boundary zones evolve. Active faults manifest themselves as steep, elongate scarps delineating the active plate boundary zone. These fault traces appear to converge and diverge, for example in the Pescadero Basin complex, in a manner similar to the Southern California borderland. The floors of the intervening basins are flat and relatively sediment free. Relict faults, also elongate fracture zones, are distinguished from active traces in that they are completely filled with hemipelagic muds. The relict faults are located along both sides of the active plate boundary zone and subparallel to it. These features infer that plate motion is relatively rapid, thus explaining the paucity of sediment accumulation in actively spreading basins in spite of high sedimentation rates. Substantial plate boundary readjustment in short time periods is suggested by the periodic abandoment and subsequent infilling and attachment of formerly active transform faults to the more stable margins of the plates involved. The Gulf of California, therefore, represents a working model of the evolution of a plate boundary and its sedimentological consequences in the early tectonic developmental stage of a passive margin ocean basin such as the Atlantic.

southern Gulf of California↗