Light hydrocarbons in Red Sea brines and sediments

Light hydrocarbon (C₁-C₃) concentrations in the water from four Red Sea brine basins (Atlantis II, Suakin, Nereus and Valdivia Deeps) and in sediment pore waters from two of these areas (Atlantis II and Suakin Deeps) are reported. The hydrocarbon gases in the Suakin Deep brine (T = ~ 25°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 85‰}$, $\text{CH}{}_4\text{=}\text{~ 71}\text{1}$) are apparently of biogenic origin as evidenced by $\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3$) ratios of ~ 1000. Methane concentrations (6–8 μl/l) in Suakin Deep sediments are nearly equal to those in the brine, suggesting sedimentary interstitial waters may be the source of the brine and associated methane.The Atlantis II Deep has two brine layers with significantly different light hydrocarbon concentrations indicating separate sources. The upper brine (T = ~ 50°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 73‰}$, CH₄ = ~ 155 μl/l) gas seems to be of biogenic origin [$\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3\text{) = ~1100}$], whereas the lower brine (T = ~ 61°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 155‰}$, CH₄ = ~ 120μl/l) gas is apparently of thermogenic origin [$\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3\text{) = ~ 50}$]. The thermogenic gas resulting from thermal cracking of organic matter in the sedimentary column apparently migrates into the basin with the brine, whereas the biogenic gas is produced in situ or at the seawater-brine interface. Methane concentrations in Atlantis II interstitial waters underlying the lower brine are about one half brine concentrations; this difference possibly reflects the known temporal variations of hydrothermal activity in the basin.     

Experimental paleotemperature equation for planktonic foraminifera

Small live individuals of Globigerinoides sacculifer which were cultured in the laboratory reached maturity and produced garnets. Fifty to ninety percent of their skeleton weight was deposited under controlled water temperature (14° to 30°C) and water isotopic composition, and a correction was made to account for the isotopic composition of the original skeleton using control groups.Comparison of. the actual growth temperatures with the calculated temperature based on paleotemperature equations for inorganic CaCO₃ indicate that the foraminifera precipitate their CaCO₃ in isotopic equilibrium. Comparison with equations developed for biogenic calcite give a similarly good fit. Linear regression with Craig's (1965) equation yields: $\text{t = ?0.07 + 1.01}\text{t}\text{?}\text{(r= 0.95)}$ where t is the actual growth temperature and $\text{t}\text{?}$ Is the calculated paleotemperature. The intercept and the slope of this linear equation show that the familiar paleotemperature equation developed originally for mollusca carbonate, is equally applicable for the planktonic foraminifer G. sacculifer.Second order regression of the culture temperature and the delta difference (δ¹⁸Oc ? δ¹⁸Ow) yield a correlation coefficient of r = 0.95: $\text{t}\text{?}\text{= 17.0 ? 4.52(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow) + 0.03(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow)}{}^2$$\text{t}\text{?}\text{, δ}{}^{18}\text{Oc}$ and δ¹⁸Ow are the estimated temperature, the isotopic composition of the shell carbonate and the sea water respectively.A possible cause for nonequilibnum isotopic compositions reported earlier for living planktonic foraminifera is the improper combustion of the organic matter.     

The effect of pressure on the solubility of minerals in water and seawater

The effect of presure on the solubility of minerals in water and seawater can be estimated from In

$\text{(}\text{K}{}^{\mathrm{P}}{}_{\mathrm{sp}}\text{K}{}^0{}_{\mathrm{sp}}\text{) +}\text{(?ΔVP + 0.5ΔKP}{}^2\text{)}\text{RT}$

where the volume (ΔV) and compressibility (ΔK) changes at atmospheric pressure (P = 0) are given by

$\text{ΔV =}\text{V}\text{?}\text{(M}{}^{\mathrm{+}}\text{, X}{}^{\mathrm{?}}\text{) ?}\text{V}\text{?}\text{[MX(s)]ΔK =}\text{K}\text{?}\text{(M}{}^{\mathrm{+}}\text{, X}{}^{\mathrm{?}}\text{) ?}\text{K}\text{?}\text{[MX(s)]}$

Values of the partial molal volume ($\text{V}\text{?}$) and compressibilty ($\text{K}\text{?}$) in water and seawater have been tabulated for some ions from 0 to 50°C. The compressibility change is quite large (~10 × 10^?3 cm³ bar^?1 mol^?1) for the solubility of most minerals. This large compressibility change accounts for the large differences observed between values of ΔV obtained from linear plots of In K_sp versus P and molal volume data (Macdonald and North, 1974; North, 1974). Calculated values of $\text{K}{}^{\mathrm{P}}{}_{\mathrm{sp}}\text{K}{}^{\mathrm{o}}{}_{\mathrm{sp}}$ for the solubility of CaCO₃, SrSO₄ and CaF₂ in water were found to be in good agreement with direct measurements (Macdonald and North, 1974). Similar calculations for the solubility of minerals in seawater are also in good agreement with direct measurements (Ingle, 1975) providing that the surface of the solid phase is not appreciably altered.     

Sedimentary iron monosulfides: Kinetics and mechanism of formation

The reaction between hydrous iron oxides and aqueous sulfide species was studied at estuarine conditions of pH, total sulfide, and ionic strength to determine the kinetics and formation mechanism of the initial iron sulfide. Total, dissolved and acid extractable sulfide, thiosulfate, sulfate, and elemental sulfur were determined by spectrophotometric methods. Polysulfides, S₄^2? and S₅^2?, were determined from ultraviolet absorbance measurements and equilibrium calculations, while product hydroxyl ion was determined from pH measurements and solution buffer capacity.Elemental sulfur, as free and polysulfide sulfur, was 86% of the sulfide oxidation products; the remainder was thiosulfate. Rate expressions for the reduction and precipitation reactions were determined from analysis of electron balance and acid extractable iron monosulfide vs time, respectively, by the initial rate method. The rate of iron reduction in moles/liter/minute was given by $\text{d(}\text{reduction}\text{Fe)}\text{dt}\text{= kS}{}_{\mathrm{t}}{}^{0.5}\text{(J}{}^{\mathrm{+}}\text{)}{}^{0.5}\text{A}{}_{\mathrm{FeOOH}}{}^1$ where S_t was the total dissolved sulfide concentration, (H⁺) the hydrogen ion activity, both in moles/ liter; and A_FeOOH the goethite specific surface area in square meters/liter. The rate constant, k, was 0.017 ± 0.002m^?2 min^?1. The rate of reduction was apparently determined by the rate of dissolution of the surface layer of ferrous hydroxide. The rate expression for the precipitation reaction was $\text{d(FeS)}\text{dt}\text{= kS}{}_{\mathrm{t}}{}^1\text{(H}{}^{\mathrm{+}}\text{)}{}^1\text{A}{}_{\mathrm{FeOOH}}{}^1$ where $\text{d(FeS)}\text{dt}$ was the rate of precipitation of acid extractable iron monosulfide in moles/liter/minute, and k = 82 ± 18 mol^?1l²m^?2 min^?1.A model is proposed with the following steps: protonation of goethite surface layer; exchange of bisulfide for hydroxide in the mobile layer; reduction of surface ferric ions of goethite by dissolved bisulfide species which produces ferrous hydroxide surface layer elemental sulfur and thiosulfate; dissolution of surface layer of ferrous hydroxide; and precipitation of dissolved ferrous specie and aqueous bisulfide ion.     

Methane-producing bacteria: natural fractionations of the stable carbon isotopes

The ${}^{13}\text{C}{}^{12}\text{C}$ fractionation factors ($\text{CO}{}_2\text{CH}{}_4$) for the reduction of CO₂ to CH₄ by pure cultures of methane-producing bacteria are, for Methanosarcina barkeri at 40°C, 1.045 ± 0.002; for Methanobacterium strain M.o.H. at 40°C, 1.061 ± 0.002; and, for Methanobacterium thermoautotrophicum at 65°C, 1.025 ± 0.002. These observations suggest that the acetic acid used by acetate dissimilating bacteria, if they play an important role in natural methane production, must have an intramolecular isotopic fractionation ($\text{CO}{}_2\text{H}\text{CH}{}_3$) approximating the observed $\text{CO}{}_2\text{CH}{}_4$ fractionation.     

Effet de la température sur les distributions de Na,Rb et Cs entre la sanidine,la muscovite,la phlogopite et une solution hydrothermale sous une pression de 1 kbar

The distribution of trace amounts of Na, Rb and Cs, between muscovite, phlogopite, sanidine and hydrothermal solution have been studied by ion exchange in a temperature range from 400 to 800°C.These distributions have been expressed with a partition ratio P^aq?m_x = $\text{(}\text{X}\text{K}\text{)}{}^{\mathrm{aq}}\text{(}\text{X}\text{K}\text{)}{}^{\mathrm{m}}$ (where X is Na, Rb or Cs).In the case of Na and Cs in muscovite, even for the dilute solutions, the ratio P^aq?m_x is not the equilibrium constant k_x of exchange reactions. In other cases, P^aq?m_x does not depend on the trace alkali ion concentration in silicates (X) and is equal to k_x. Variations of P_x or k_x with T are greater for Na and Cs than for Rb. Generally, k_x decreases with increase in T. The function log $\text{P}{}_{\mathrm{x}}\text{= f(}\text{1}\text{T}\text{)}$ is not linear for Na or Cs, but in the case of Rb, $\text{f(}\text{1}\text{T}\text{)}$ is linear and the standard enthalpy and entropy of exchange reactions have been estimated by applying the Arrhenius relation.The distribution relations obtained between silicate and vapour phase permit the determination of distributions of Na, Rb and Cs between two minerals mI and mII, relative to K. These have been expressed with the partition ratio Q_x =$\text{(}\text{X}\text{K}\text{)}{}^{\mathrm{mI}}\text{(}\text{X}\text{K}\text{)}{}^{\mathrm{mII}}$. Variations of Q_x with T are not remarkable, and even for Rb between phlogopite and feldspar are negligible. Nevertheless, one may use the distributions of Rb and Cs between muscovite and feldspar for geothermometry. Experimental results have been applied to some rocks by effecting corrections from the major element composition of the natural minerals. Estimated temperatures are near to 400°C in the granites and pegmatite studied here.     

Radium isotopes in saline seepages,south-western Yilgarn,Western Australia

Water samples from saline seepages in the south-western Yilgarn Block of Western Australia contain high activities of the four naturally-occurring radium isotopes. Activities of up to 310 $\text{pCi}\text{l}$ for ²²⁶Ra and 1720 $\text{pCi}\text{l}$ for ²²⁸Ra were measured and the ${}^{228}\text{Ra}{}^{226}\text{Ra}$ ratio averaged 6.1. Activities of the two short-lived radium isotopes were also high. ²²³Ra activities of up to 94 $\text{pCi}\text{l}$ were found with an average ${}^{226}\text{Ra}{}^{223}\text{Ra}$ ratio of 3.3, considerably lower than the natural abundance ratio of 21.4. Activities of up to 23 $\text{pCi}\text{l}$²²⁷Ac, the long-lived ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 22 years}$) grandparent of ²²³Ra, were also measured. The analysis of surface granite samples, the probable source rocks of the radium, gave $\text{Th}\text{U}$ activity ratios of around 1.5. The higher ${}^{228}\text{Ra}{}^{226}\text{Ra}$ ratios of the waters were attributed to readily leached ²²⁸Ra in the weathered granites as a result of thorium remaining after weathering. Leach experiments on U-Th ore by NaCl solutions showed that all four radium isotopes were equally leached. Sulphate anions reduced the ²²⁶Ra and ²²⁸Ra leaching to a greater extent than for ²²³Ra and ²²⁴Ra, suggesting that the latter isotopes were being supported in solution by parent isotopes. In particular this suggested ²²⁷Ac was leached into the sulphate solution but this does not fully account for the amount of ²²⁷Ac seen in the seepage waters.     

Extension of the empirical Alyavdin equation for representing batch grinding data

The Alyavdin equation for batch grinding data is:

$\text{1 ? P(χ, t) = [1 ? P(χ, 0)]}\text{exp}\text{?}\text{c(x)t}{}^{\mathrm{p}}\text{]}$

where P(χ,t) is the weight fraction less than size χ after grinding time t, c (χ) is constant with t and p is a constant close to one. It is shown that this equation is illogical (except for a single size of feed) unless c (χ) varies with P(χ,0), which makes the equation of little utility. A new empirical equation is developed for finite size intervals:

which reduces to the Alyavdin equation for a single size of feed, and which gives consistent computations for any feed size distribution. Techniques are given for determining K_i, γ values from sets of batch grinding data. The values are then used to predict size distributions for other times and other feed size distributions. The equation was quite successful in predicting size distributions in batch milling: (a) providing the feed size distribution was not un-natural, that is, not truncated or (b) if a truncated feed was used, the values of K_i and γ are determined from size distributions of grinding of the same type of feed. Thus, K_i, γ are not, unfortunately, completely independent of the starting feed size distribution.     

Experimental hydrogen isotope studies—I. Systematics of hydrogen isotope fractionation in the systems epidote-H2O,zoisite-H2O and AlO(OH)-H2O

$\text{H}\text{D}$ Fractionation factors between epidote minerals and water, and between the AlO(OH) dimorphs boehmite and diaspore and water, have been determined between 150 and 650°C. Small water mineral ratios were used to minimise the effect of incongruent dissolution of epidote minerals. Waters were extracted and analysed directly by puncturing capsules under vacuum. Hydrogen diffusion effects were eliminated by using thick-walled capsules.$\text{H}\text{D}$ Exchange rates are very fast between epidote and water (and between boehmite and water), complete exchange taking only minutes above 450°C but several months at 250°C. Exchange between zoisite and water (and between diaspore and water) is very much slower, and an interpolation method was necessary to determine fractionation factors at 450 and below.For the temperature range 300–650°C, the $\text{H}\text{D}$ equilibrium fractionation factor (α^e) between epidote and water is independent of temperature and Fe content of the epidote, and is given by 1000 In α_epidote-H2O^e = ?35.9 ± 2.5, while below 300°C 1000 In , with a ‘cross-over’ estimated to occur at around 185°C. By contrast, zoisite-water fractionations fit the relationship 1000 In .All studied minerals have hydrogen bonding. Fractionations are consistent with the general relationship: the shorter the O-H -- O bridge, the more depleted is the mineral in D.On account of rapid exchange rates, natural epidotes probably acquired their H-isotope compositions at or below 200°C, where fractionations are near or above 0%.; this is in accord with the observation that natural epidotes tend to concentrate D relative to other coexisting hydrous minerals.     

The variation of the marine 87Sr86Sr ratio during Phanerozonic time: interpretation using a flux model

The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio in sea water has varied over geologic time due to the addition of strontium to the sea from rocks with a variety of ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios. The measurements by Petermanet al. (Geochim. Cosmochim. Acta34, 105–120, 1970) of the value of the marine ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio have been confirmed by several other workers and by some new measurements on JOIDES samples. They form the basis of a model calculation of the relative proportions of ‘basaltic’ (${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.704}$) and ‘granitic’ (${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.718}$) strontium being supplied to the sea. For the last 200 million years, the proportions of these two sources appear to reflect the history of global tectonics; ‘basaltic’ during rifting and increasingly ‘granitic’ during the present episodes of uplift and continental collision     

Transfer and exchange equilibria in a portion of the pyroxene quadrilateral as deduced from natural and experimental data

Differences in the chemical composition of metamorphic and igneous pyroxene minerals may be attributed to a transfer reaction, which determines the Ca content of the minerals, and an exchange reaction, which determines the relative Mg:Fe²⁺ ratios. Natural data for associated Ca pyroxene (Cpx) and orthopyroxene (Opx) or pigeonite are combined with experimental data for Fe-free pyroxenes, to produce the following equations for the Cpx slope of the solvus surface: $\text{> 1080°C: T =}\text{1000}\text{(0.468 + 0.246X}{}^{\mathrm{Cpx}}\text{? 0.123 ln (1–2 [Ca]))}$$\text{< 1080°C: T =}\text{1000}\text{(0.054 + 0.608X}{}^{\mathrm{Cpx}}\text{? 0.304 ln (1–2 [Ca]))}$, and the following equation for the temperature-dependence of the Mg-Fe distribution coefficient: $\text{T =}\text{1130}\text{(}\text{ln}\text{K}{}_{\mathrm{p}}\text{+ 0.505)}$, where T is absolute temperature, X is $\text{Fe}{}^{\mathrm{2+}}\text{(Mg + Fe}{}^{\mathrm{2+}}\text{))}$, [Ca] is $\text{Ca}\text{(Ca + Mg + Fe}{}^{\mathrm{2+}}\text{)}$ in Cpx, and K_D is the distribution coefficient, defined as $\text{X}{}^{\mathrm{Opx}}\text{/(1 ? X}{}^{\mathrm{Opx}}\text{) ÷ X}{}_{\mathrm{Cpx}}\text{/(1 ?}{}^{\mathrm{Cpx}}\text{)}$.The transfer and exchange equations form useful temperature indicators, and when applied to 9 sets of well-studied rocks, yield pairs of temperatures that are in good agreement. For example, temperatures obtained for the Bushveld Complex are 1020°C (solvus equation) and 980°C (exchange equation), based on 7 specimens. The uncertainty in these numbers, due to precision and accuracy errors, is estimated to be ±60°.     

Carbonate equilibria in hydrothermal systems: First ionization of carbonic acid in NaCl media to 300°C

The ionization quotients of aqueous carbon dioxide (carbonic acid) have been precisely determined in NaCl media to 5 m and from 50° to 300°C using potentiometric apparatus previously developed at Oak Ridge National Laboratory. The pressure coefficient was also determined to 250°C in the same media. These results have been combined with selected information in the literature and modeled in two ways to arrive at the best fits and to derive the thermodynamic parameters for the ionization reaction, including the equilibrium constant, activity coefficient quotients, and pressure coefficients. The variation with temperature of the two fundamental quantities $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ and $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ were examined along the saturation vapor pressure curve and at constant density. The results demonstrated again that for reactions with minimal electrostriction changes the magnitudes and variations of $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ with temperature are small and, in addition, $\text{Δ}\text{C}\text{?}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}$ are approximately independent of salt concentration.The results have also been applied to an examination of the solubility of calcite as a function of pH (in a given NaCl medium) for the neutral to acidic region both for systems with fixed CO₂ pressure and systems where the calcium ion concentration equals the concentration of carbon. The pH of saturated solutions of calcite with P_CO2 of 12 bars increases from 5.1 to 5.5 between 100° and 300°C.     

Strontium isotopic composition of some brines from the Precambrian Shield of Canada

Twenty-four groundwater samples from seven operating mines at Sudbury, Yellow-knife and Thompson (Ontario, North West Territories and Manitoba, resp.), all from depths greater than 1 km and ranging in total dissolved solids (TDS) from 1900 to 250,000 mg l^?1, were measured for their ${}^{87}\text{Sr}{}^{86}\text{Ar}$ values. Each geographic location gives a limited range in values and each location is distinct from the others. This is interpreted as the result of extensive water-rock interaction on a local scale. For most of the time, these brines were isolated and only recently have been exposed to surface water as a result of the mining operations. The extent of the isolation is shown by the contrasting isotopic values of two “pockets” of water (0.711 vs. 0.716) located on opposite sides of the same fault system on the North Range at Sudbury. The exchange at all sites probably has continued until the present, as indicated by the close agreement between water and present-day${}^{87}\text{Sr}{}^{86}\text{Sr}$ whole-rock values. If so, it suggests that there is no single age for such brines, but it may be possible to date stages in the water's evolution by determining the age of secondary minerals that equilibrated with the water.     

Strontium isotope geology of the South Mountain batholith,Nova Scotia

The South Mountain batholith of southwestern Nova Scotia is a large, peraluminous, granodiorite-granite complex which intrudes mainly greenschist facies metasediments of the Cambro-Ordovician Meguma Group. Using Rb-Sr isochrons constructed from whole rocks and mineral separates, the present study shows a variation in age and initial ratios of the intrusive phases of the batholith as follows: biotite granodiorite (371.8 ± 2.2 Ma, (${}^{87}\text{Sr}{}^{86}\text{Sr}\text{)}{}_{\mathrm{i}}$ ranges from 0.7076 ± 0.0003 to 0.7090 ± 0.0003, with the average = 0.7081); adamellite (364.3 ± 1.3 Ma, $\text{(}{}^{87}\text{Sr}{}^{86}\text{Sr}\text{)}{}_{\mathrm{i}}\text{= 0.70942 ± 35}$); porphyry (361.2 ± 1.4 Ma, $\text{(}{}^{87}\text{Sr}{}^{86}\text{Sr}\text{)}{}_{\mathrm{i}}\text{= 0.71021 ± 119}$); using λ⁸⁷Rb = 1.42 × 10^?11yr^?1.A suite of Meguma country rock samples showed a variation of ${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.7113?0.7177}$ at the time of intrusion of the batholith. A number of xenoliths of this material occurring in the marginal granodiorite had partially equilibrated isotopically with the granodiorite at a higher ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio than elsewhere in the granodiorites. This evidence demonstrates that isotopic (and probably some accompanying bulk chemical) contamination by the Meguma rocks has been an important factor in determining the ultimate chemical composition and mineralogy of the South Mountain batholith.The $\text{(}{}^{87}\text{Sr}{}^{86}\text{Sr}\text{)}{}_{372}\text{= 0.7081}$ of the early granodiorites indicates that the parent magma of the South Mountain batholith was derived from a source unlike the Meguma Group. The precise nature of the source region cannot be determined by Rb-Sr work unless the degree of contamination with Megumalike material is known.     

UThPb systematics of the eucrite “Juvinas”: Precise age determination and evidence for exotic lead

The U-Th-Pb isotope systematics of the eucrite “Juvinas” have been studied in whole rock fragments as well as in plagioclases and pyroxenes. The results show that this monomict breccia crystallized with a very high $\text{U}\text{Pb}$ initial ratio at T = 4.539 ± 0.004 AE ago. There is evidence for a less radiogenic Pb component (${}^{206}\text{Pb}{}^{204}\text{Pb}\text{= 13.0}$; ${}^{207}\text{Pb}{}^{204}\text{Pb}\text{= 13.5}$; ${}^{208}\text{Pb}{}^{204}\text{Pb}\text{= 32.71}$) interpreted as “exotic lead” induced by a meteoritical impact at the surface of the Juvinas parent body, 1.92 ± 0.06 AE ago.     

Intensive sampling of noble gases in fluids at Yellowstone: I. Early overview of the data; regional patterns

The Roving Automated Rare Gas Analysis (RARGA) lab of Berkeley's Physics Department was deployed in Yellowstone National Park for a 19 week period commencing in June, 1983. During this time 66 gas and water samples representing 19 different regions of hydrothermal activity within and around the Yellowstone caldera were analyzed on site. Routinely, the abundances of five stable noble gases and the isotopic compositions of He, Ne, and Ar were determined for each sample. In a few cases the isotopes of Kr and Xe were also determined and found to be of normal atmospheric constitution.Correlated variations in the isotopic compositions of He and Ar can be explained within the precision of the measurements by mixing of only three distinct components. The first component is of magmatic origin and is enriched in the primordial isotope ³He with ${}^3\text{He}{}^4\text{He}\text{≥ 16}$ times the air value. This component also contains radiogenic ⁴⁰Ar and possible ³⁶Ar with ${}^{40}\text{Ar}{}^{36}\text{Ar}\text{≥ 500}$, resulting in a ${}^3\text{He}{}^{36}\text{Ar}$ ratio ≥ 41,000 times the air value. The second component is assumed to be purely radiogenic ⁴He and ⁴⁰Ar (${}^{41}\text{He}{}^{401}\text{Ar}\text{= 4.08 ± .33}$). This component is the probable carrier of observed excesses of ²¹¹Ne, attributed to the α,n reaction on ¹⁸O. Its radiogenic character implies a crustal origin in U. Th, and Krich aquifer rocks. The third component, except for possible mass fractionation, is isotopically indistinguishable from the noble gases in the atmosphere. This component originates largely from infiltrating run-off water saturated with atmospheric gases.In addition to exhibiting nucleogenic ²¹¹Ne, Ne data show anomalies in the ratio ${}^{20}\text{Ne}{}^{20}\text{Ne}$, which correlate roughly with the ${}^{21}\text{Ne}{}^{22}\text{Ne}$ anomalies for the most part, but not as would occur from simple mass fractionation. Some exaggerated instances of the ${}^{20}\text{Ne}{}^{22}\text{Ne}$ anomaly occur which could be explained by combined mass fractionation of Ne and Ar isotopes to a severe degree coupled with remixing with normally isotopic gases. Otherwise exotic processes have to be invoked to explain the ²⁰Ne data.Relative abundances of the non-radiogenic and non-nucleogenic noble gases (²²Ne, ³⁶Ar, ⁸⁴Kr, and ¹³²Xe) are highly variable but strongly correlated. High Xe/Ar ratios are always accompanied by low Ne/ Ar ratios and vice versa. Except for water from the few cold (T < 20°C) springs analyzed, none of the samples have relative abundances consistent with air saturated water and the observed variations are not readily explained by the distillation of air saturated water.In characterizing each area of hydrothermal activity by the highest ${}^3\text{He}{}^4\text{He}$ ratio found for that area, we find that within the caldera this parameter is somewhat uniform at ~7 ± 1 times the air value. There are exceptions, most notably at Mud Volcano, an area located along a crest of recent and rapid uplift. Here the maximum ${}^3\text{He}{}^4\text{He}$ ratio is ~ 16 times the air value. Also noteworthy is Gibbon Basin which is in the vicinity of the most recent rhyolitic volcanism and exhibits a ${}^3\text{He}{}^4\text{He}$ ratio ~ 13 times the air value. Immediately outside the caldera the maximum $\text{sol}{}^3\text{He}{}^4\text{He}$ ratio decreases rapidly to values < ~3 times the air value.     

The thermal significance of potassium feldspar K-Ar ages inferred from 40Ar39Ar age spectrum results

${}^{40}\text{Ar}{}^{39}\text{Ar}$ age spectrum analyses of three microcline separates from the Separation Point Batholith, northwest Nelson, New Zealand, which cooled slowly (~5°C-Ma^?1) through the temperature zone of partial radiogenic ⁴⁰Ar accumulation are characterized by a linear age increase over the first 65 percent of gas release with the lowest ages (~80 Ma) corresponding to the time that the samples cooled below about 100°C. The last 35 percent of ³⁹Ar released from the microclines yields plateau ages (103,99 and 93 Ma) which reflect the different bulk mineral ages, and correspond to cooling temperatures between about 130 to 160°C. Theoretical calculations confirm the likelihood of diffusion gradients in feldspars cooling at rates ≤5°C-Ma^?1. Diffusion parameters calculated from the ³⁹Ar release yield an activation energy, E = 28.8 ± 1.9 kcal-mol^?1, and a frequency factor/grain size parameter, $\text{D}{}_0\text{l}{}^2\text{= 5.6}{}_{\mathrm{?3.9}}{}^{\mathrm{+14}}\text{sec}{}^{\mathrm{?1}}$. This Arrhenius relationship corresponds to a closure temperature of 132 ± 13°C which is very similar to the independently estimated temperature. From the observed diffusion compensation correlation, this $\text{D}{}_0\text{l}{}^2$ implies an average diffusion half-width of about 3 μm, similar to the half-width of the perthite lamellae in the feldspars. The range in microcline K-Ar ages from the Separation Point Batholith is the result of relatively small temperature differences within the pluton during cooling. Comparison of the diffusion laws determined for microcline with those for anorthoclases and other homogeneous K-feldspars (E = 40 to 52 kcal-mol^?1) reveals that Ar diffusion is more highly temperature dependent in the disordered structural state than in the ordered structural state. Previously published U-shaped age spectra are probably the result of the superimposition of excess ⁴⁰Ar upon diffusion profiles of the kind described here.     

Diffusion of ions in sea water and in deep-sea sediments

The tracer-diffusion coefficient of ions in water, D_j⁰, and in sea water, $\text{D}{}_{\mathrm{j}}{}^1$, differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective $\text{D}{}_{\mathrm{j}}{}^1$ or D_j⁰ values. The tracer diffusion coefficients of ions in deep-sea sediments, D_j,sed., can be related to $\text{D}{}_{\mathrm{j}}{}^1$ by $\text{D}{}_{\mathrm{j,sed.}}\text{= D}{}_{\mathrm{j}}{}^1\text{·}\text{α}\text{θ}{}^2$, where θ is the tortuosity of the bulk sediment and a a constant close to one.     

Density calculations for silicate liquids. I. Revised method for aluminosilicate compositions

Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature T_r, is given by $\text{V}{}_{\mathrm{r}}\text{= ∑X}{}_{\mathrm{i}}\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{i}}\text{+ X}{}_{\mathrm{A}}\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$, where the summation is taken over all oxide components except A1₂O₃, X stands for mole fraction, terms are constants derived independently from an analysis of volume-composition relations in alumina-free silicate liquids, and $\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is the composition-dependent apparent partial molar volume of Al₂O₃. The thermal expansion coefficient of aluminosilicate liquids is given by $\text{α = ∑X}{}_{\mathrm{i}}\text{}\text{?}\text{ga}{}_{\mathrm{i}}{}^{\mathrm{o}}\text{+ X}{}_{\mathrm{A}}\text{}\text{?}\text{ga}{}_{\mathrm{A}}{}^{\mathrm{o}}$, where $\text{}\text{?}\text{ga}{}_{\mathrm{i}}{}^{\mathrm{o}}$ terms are constants independent of temperature and composition, and $\text{}\text{?}\text{ga}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is a composition-dependent term representing the effect of Al₂O₃ on the thermal expansion. Parameters necessary to calculate the volume of silicate liquids at any temperature T according to V(T) = V_rexp[α(T-T_r)], where T_r = 1400°C have been evaluated by least-square analysis of selected density measurements in aluminosilicate melts. Mean molar volumes of aluminosilicate liquids calculated according to the model equation conform to experimentally measured volumes with a root mean square difference of 0.28 $\text{cc}\text{mole}$ and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of $\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is discussed in terms of several possible interpretations of the structural role of Al³⁺ in aluminosilicate melts.