Showing papers in "Geochemical Journal in 1983"

Evaporation metamorphism in the early solar nebula. Evaporation experiments on the melt FeO-MgO-SiO2-CaO-Al2O3 and chemical fractionations of primitive materials.

Abstract: Evaporation experiments were performed in vacuo on the multicomponent melt, FeO-MgO-SiO2-CaO-Al2O3 with the solar elemental abundances. The analysis of experimental results shows that the rate-determining step of evaporation is the vaporization reactions occurring on the melt surface, amongst other possible rate processes. The reaction modes are determined for the components, FeO, MgO and SiO2. FeO, unlike other components, vaporizes through the disproportionation reaction into metallic and ferric irons in the melt phase. ‘Volatility’ is defined as a physical quantity so as to describe the evaporational fractionations of elements. On the basis of this concept, the experimental results of the present and previous works together with thermodynamic data are organized to characterize the evaporation sequence of primitive condensed materials. Its gross feature is the sequential evaporation of the components in the order of Fe, Mg, Si, Ca and Al. The details of the evaporation sequence depend on temperature and initial valences of Fe. The evaporation sequence is comparatively discussed with the condensation sequence of the nebular gas, which has been well examined by previous workers. Both sequences, combined together, provide a basic framework to clarify the chemical fractionation processes which have differentiated primitive materials into the planetary and meteoritic materials. The chemical diversity of chondrules and inclusions in meteorites is interpreted as mainly due to the evaporational or condensational fractionation, but it also invokes other processes such as metal/silicate separation and non-equilibrium reaction with a surrounding gas.

Nitrogen isotope ratio of atmospheric N2O as a key to the global cycle of N2O

Abstract: An analytical system to separate N2O in the air was developed to measure the δ15N value and concentration of N2O. The system was designed so that δ15N value and concentration of ca. 1 μmol N2O from ca. 60 l air could be measured with the accuracy of ±0.2‰ and ±10 ppbv, respectively. Air samples were collected at three individual sites in Japan. The average values of δ15N and concentration of N2O for 32 samples with the standard deviation were +8.1 ± 1.0‰ and 316 ± 14 ppbv, respectively. The diversity of the observed data was attributed to the change in the mixing ratio of air masses of different characteristics. A discussion was made on the global cycle of N2O. Bacterial reduction of N2O was proposed to be the major consuming process of N2O on the Earths surface.

K-Ar ages of dikes in Northeast Japan.

Abstract: Thirteen dike swarms in Northeast Japan were dated by the K-Ar method. The K-Ar ages in this study give some crucial constraints to the volcanostratigraphy and imply that the geological situation of some dike swarms estimated in the other studies should be reexaminned while other dike swarms showed the K-Ar ages concordant with the geological ages. Available K-Ar ages of the volcanic rocks from the present and other studies indicate that the volcanic front in Northeast Japan had a temporal position about 22–23 Ma ago to the east of that in the Quaternary and that the volcanism appears to have been inactive from 17 to 21 Ma ago.

Comprehensive strontium isotope study of Quaternary volcanic rocks from the Izu-Ogasawara arc

Abstract: In the Izu-Ogasawara arc, many Quaternary volcanoes are located in a line parallel to the Izu-Ogasawara Trench. 87Sr/86Sr ratios were determined for 65 samples of Quaternary volcanic rocks, 4 cognate inclusions and one sample of basement rock from 15 volcanic islands and 3 submarine volcanoes. In this arc, the 87Sr/86Sr ratios in several rocks from the same volcano agree with one another within 0.0002, regardless of the difference of the rock types and the eruptive stages. The ratios of the volcanoes along the volcanic front in the Izu-Ogasawara arc were constant over 1, 200 km and were all within the range between 0.7034 and 0.7039, which is significantly lower than those from the Northeast Japan arc (0.7038–0.7044) (NOTSU, 1983). In the northern region of the Izu-Ogasawara arc, across-arc 87Sr/86Sr ratio variation was found. The ratios decrease with increasing depth of the Wadati-Benioff zone. Even in the volcanic rocks distant from the volcanic front, the ratios (0.7033–0.7035) were slightly higher than those in normal-type MORB, so it is suggested that a small amount of oceanic sediment, altered basalt or sea water component that accompanies the subducting slab has been contributed to the source magma which originates from a partially melted, upper mantle wedge. This contribution becomes smaller with increasing distance from the volcanic front.

Ordering of Opal-CT in diagenesis

Abstract: Opal-CT in sediments is formed from opal-A and is converted to quartz during diagenesis. In that process, opal-CT becomes progressively ordered as is distinctly indicated by the decrease in d(101) spacing. Based on a kinetic equation experimentally found by KANO (1979) and KANO and TAGUCHI (1982), the decreasing rate of d(101) spacing has been calculated from previously reported d(101) spacings (MITSUI, 1975) and thermal history of sediments in a borehole, MITI Hamayuchi. The calculated rate makes a subtle difference between the reported and calculated d(101) spacings, suggesting the availability of the equation applied. However, even if compared at the same temperature, the rate is much slower than that in hydrothermal alkaline conditions. Thus, the ordering process of opal-CT is more or less chemically controlled. Taking the thermal history of sediments into account, a model based on the kinetic equation well fits the previously reported relationship between the d(101) spacing of Neogene siliceous sediments and the maximum temperature to which the sediments have been subjected (IIMIMA and TADA, 1981), suggesting that the ordering process of opal-CT in diagenetic conditions is controlled mainly by temperature. The features of distribution of d(101) spacing in sediment piles have been discussed by using the model.

Geochemical investigations of kimberlites from the Kimberley area, South Africa

Abstract: Fifteen major components and 21 trace elements (Li, F, S, Cl, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Cd, Ba, Hg, Tl, Pb and Bi) were analyzed for 11 kimberlites and 3 xenoliths (garnet peridotite, eclogite and gabbro) from South Africa. Selected major and trace element contents of olivine, serpentine, pyroxene, phlogopite, perovskite, spinel, magnetite, Fe-Ni-Cu-S ores and native copper in several kimberlites were also measured. Sulfur isotope compositions of 5 kimberlites and a garnet peridotite range from δ34S -3 to +9.6‰. The concentrations of major elements and Cr, Co, Ni, Zn, Hg have a small, but those of Li, Na, K, Rb, Cl and Tl a wide range of variation. Good correlations of K-Rb have to be mentioned. Large Fe2O3/FeO ratios indicate relatively high oxygen fugacities during eruption. Additional data on about 60 elements in bulk kimberlites have been compiled from the literature to estimate the average chemical composition of kimberlites. In order to know the accumulation and depletion of elements during magma formation, the elemental abundances of kimberlites were compared with those of undepleted mantle rocks. Kimberlites are characterized by very high concentrations of incompatible and volatile elements such as La, Ce, C, Nd, Th, U, F, Cs, Nb, Sm, Ta, Rb, Ba, K, P, Pb and Sr, and low concentrations of Si, Na, Al and heavy REE. Concentrations of the former elements suggest that kimberlite magmas are produced by a small degree of partial melting in the presence of CO2 and H2O under upper mantle conditions.

K-Ar ages of dikes in Southwest Japan.

Abstract: Eleven samples from six dike swarms in Southwest Japan were dated by the K-Ar method. Most K-Ar ages obtained for these samples indicate that a volcanism as dike intrusions occurred about 15 Ma ago at some areas in the inner zone of Southwest Japan. The previous geochronological studies by other workers have already revealed the occurrence of granitic intrusions and their related effusive rocks at about 14 Ma ago in the outer zone of Southwest Japan. Hence, it is inferred that the igneous activity was intensive in the relatively wide regions of Southwest Japan about 15 Ma ago.

Lead isotopes as indicators of old stable craton in Western Australia

Abstract: After some discussion of analytical adequacy, Pb-isotope ratios are presented for galenas from the north-west of Western Australia. The data, all double-spike normalised, subdivide into three distinguishable groups in their relationship to the Cumming-Richards Pb-growth Model III. As noted previously, samples with model age 2.7Ga or older exhibit a higher-than-average source Th/U, and a normal dependence of source U/Pb (μ = 238U/204Pb) on country-rock chemical type. Younger samples, on the other hand, exhibit uniformly high μ-values, regardless of host-rock chemistry, and two distinguishable Th/U regimes. For 206Pb/204Pb in the range 14.0–16.5, source Th/U values are close to growth-curve average, whereas for younger samples, 208Pb/204Pb is observed to be very high. The data seem best interpreted in terms of two ‘events’ involving migration of uranium. In the first, at a time near the defined Archaean-Proterozoic boundary, there appears to have been incursion of U into the Pb-source, at a time close to ‘cratonisation’ of the region. The second event, late in the Precambrian, appears to have involved loss of U from the system. Some parallelisms between the isotopic histories of Western Australia and southern Africa are noted.

Synthetic studies of protodolomite from brine waters.

Abstract: Synthetic studies of protodolomite were carried out for understanding the conditions of protodolomite formation in sedimentary environments. Protodolomite was tried to be precipitated from concentrated sea water (by evaporating sea water) by adding 0.4M-Na2CO3 solution drop by drop. The obtained minerals were amorphous carbonate, aragonite, Mg-poor calcite, Mg-rich calcite, protodolomite, huntite, monohydromagnesite, monohydrocalcite and trihydrocalcite, depending on the concentrations of calcium and magnesium ions in the brine water, the added amount of sodium carbonate and reaction time. Protodolomite seems to be formed diagenetically from metastable minerals given above. The concentration of carbonate ions, Mg2+/Ca2+ ratio and temperature in a parent solution have an important influence on the formation of calcite type carbonate minerals and the Mg contents of these minerals.

Stenols and phytol in lake sediments from Syowa and Vestfold Oases in the Antarctic

Abstract: Phytol and stenols were studied for lake sediments from Syowa and Vestfold Oases in the Antarctic. Phytol and 6 stenols (cholesta-5, 22-dien-3β-ol, cholest-5-en-3β-ol, 24-methylcholesta-5, 22-dien-3β-ol, 24-methylcholest-5-en-3β-ol, 24-ethylcholesta-5, 22-dien-3β-ol and 24-ethylcholest-5-en-3β-ol) were found, with concentrations ranging from 0.099 to 38 and 0.079 to 9.0μg g-1 dry sediment, respectively. The dominant stenols are cholest-5-en-3β-ol, 24-methylcholest-5-en-3β-ol and 24-ethylcholest-5-en-3β-ol. These compounds must be derived mainly from green and blue-green algae, diatoms and mosses. The relative abundances of these stenols should reflect the difference of source organisms in the lakes and the surroundings.

Sulfur isotope ratios of the Akatani, Iide and Waga-Sennin skarn deposits, and their bearing on mineralizations in the "Green Tuff" region, Japan.

Abstract: Sulfur isotope ratios of sulfide minerals from the Akatani, Iide and Waga-Sennin skarn deposits formed in the “Green Tuff” region, fall in a rather broad range from +2.8 to +8.9‰. Estimated formation conditions of ores, that is, high oxygen fugacities and relatively low temperatures and pH, certify the predominance of sulfate sulfur over sulfide sulfur in the ore-forming solutions. Irreversible, fast precipitation of sulfide minerals from such sulfate-dominant solutions is thought to have resulted in insignificant isotopic fractionation between aqueous sulfate and sulfide minerals. The obtained range of isotopic values is almost identical with those for sulfide minerals from other type, vein and kuroko, deposits in the “Green Tuff” region. This regularity of sulfur isotope values for many different type deposits in the region suggests the possibility that ore sulfur was supplied from a common provenance, such as Miocene felsic igneous rocks, without any significant isotopic fractionations in the transportation and precipitation processes.

Behavior of 7Be in Funka Bay, Japan, with reference to those of insoluble nuclides, 234Th, 210Po and 210Pb.

Abstract: 7Be in seawater and sediment trap samples in Funka Bay, Japan was determined together with 210Pb, 210Po and Th isotopes. The sampling was carried out in summer in 1977 and 1979, when the Bay constituted a closed system for mixing with water outside the Bay. The concentration of 7Be of atmospheric origin in seawater did not monotonously decrease with depth, but showed a weak maximum in the intermediate layer. The layer also contained larger amounts of 234Th, 210Po and 210Pb in summer, 1979. The results obtained from sediment trap samples suggest that significant portions of these nuclides and some other heavy metals are transported downward by particulate matter. The residence time of Be in Funka Bay (mean depth 60m) was calculated to be 90–160 days from the activity ratio of 7Be/234Th of the trapped material and the removal rate of 234Th from seawater obtained from the disequilibrium with 238U. These facts also support the TSUNOGAI and MINAGAWA's settling model for the removal of isoluble metals from seawater rather than the irreversible removal from seawater and the rapid transport of these metals in particles.

Incorporation of fluoride ions into calcite—Effect of organic materials and magnesium ions in a parent solution

Abstract: The effect of citrate, malate, lactate and acetate ions in a parent solution on the incorporation of fluoride ions into formed calcite has been studied experimentally. Citrate ions in a parent solution containing no magnesium ions increase intensively the amount of fluoride ions incorporated into magnesium-free calcite, and malate ions do so but moderately, while lactate and acetate ions have little effect on the incorporation of fluoride ions into calcite. The amount of fluoride ions incorporated into low Mg-calcite (smaller than 4% magnesium carbonate) formed from a parent solution containing magnesium ions but no citrate ions remarkably increases with increasing magnesium carbonate content of the formed low Mg-calcite. This trend is in agreement with that observed in marine calcareous skeletons (OHDE and KITANO, 1980). The amount of fluoride ions incorporated into high Mg-calcite formed from a parent solution containing both magnesium and citrate ions is large. The fluoride amount slightly increases with increasing magnesium carbonate content of the formed high Mg-calcite.

10Be and 10Be/9Be in manganese nodules

Abstract: Depth profiles of 10Be and 9Be concentrations have been measured in five manganese nodules from widely varying locations of the Pacific Ocean. Mean accumulation rate of these manganese nodules ranges from 2.7 to 8.0 mm·m.y.-1. The variation of 10Be and 10Be/9Be with depth or time is found to be less than ±30% for periods from 0.4–1.0 m.y. back to 6 m.y. B.P. Surface 10Be/9Be atomic ratio is found to be (9–13) × 10-8, that shows authigenic nature of manganese nodule acuumulation by comparison with (12–31) × 10-8 for deep-sea water, (2–7) × 10-8 for clay sediments and (7–9) × 10-8 for fossil-rich sediments.

Removal of anions by carbonate sedimentation from seawater.

Abstract: The authors show the removal of fluoride, chloride, sulfate, phosphate, borate ions and soluble silica from seawater by marine carbonate sedimentation. The authors have estimated the amounts of anions and soluble silica discharged into seawater and those of anions and soluble silica removed from seawater by marine carbonate sedimentation. The balance between both amounts estimated indicates that the significant portions of fluoride, phosphate and borate ions discharged into seawater are removed from seawater by marine carbonate sedimentation.

Deuterium fractionation between water vapor and hydrogen gas in fumarolic gases.

Abstract: The fumarolic condensate and hydrogen gas samples collected from the Showashinzan, Nasudake, Yakedake and Kuju-Ioyama volcanoes, Japan, have been analyzed for the D/H ratio. A comparison between temperatures for isotopic equilibrium and measured outlet temperatures indicates that in high temperature fumarolic gases the deuterium exchange reaction between water vapor and hydrogen gas is rapid enough to readjust the equilibrium to the outlet temperature of fumaroles. For low temperature fumarolic gases, however, the isotopic temperature refers to equilibrium conditions deep in the fumarole.

Fractionation of sulfur isotopes and selenium between coexisting pyrite and chalcopyrite from the Hitachi deposits, Ibaraki Prefecture, Japan.

Abstract: Sulfur isotopes and selenium/sulfur ratios were determined for coexisting pyrite and chalcopyrite from the Kieslager-type deposits of the Hitachi mine, Ibaraki Prefecture, Japan. All pyrite-chalcopyrite pairs analyzed exhibit the normal isotope fractionation, i.e., 34S is more enriched in pyrite than in chalcopyrite. Selenium is more enriched conversely in chalcopyrite than in pyrite. The mean δ34S differences between pyrite and chalcopyrite are 0.84±0.44‰ (11) for the ore bodies of the epidote-amphibolite facies and 0.54±0.24‰ (12) for those of the amphibolite facies. It seems too optimistic, however, to regard the observed differences in the mean value between the two facies as indicating the difference in metamorphic temperature between the two facies, because the magnitude of isotope fractionation is rather variable even within the single ore bodies. Partition of selenium between pyrite and chalcopyrite was found to be virtually the same for both the facies. The mean distribution coefficients of selenium, Dcp-py, are 4.26±0.85 (12) for the epidote-amphibolite facies and 4.44±1.60 (13) for the amphibolite facies. Near-equilibrium trend in sulfur isotope fractionation and rather consistent partition of selenium between pyrite and chalcopyrite strongly suggest that selenium equilibrium is also approached between the two minerals in the Hitachi deposits.

Origin of calc-alkalic andesites, Nasu zone, northeastern Japan: Kuno revisited.

Abstract: KUNO (1950, 1959) first identified the existence of two rock series in the Japanese volcanic arc and proposed the origin of one from the other by assimilation of granitic material. In the Nasu zone in northeastern Japan, both the tholeiitic suite with pigeonite in the groundmass and the calc-alkalic suite with hypersthene as the Ca-poor pyroxene in the groundmass have been shown to have erupted from one volcano and to have differences in major element chemistries (KAWANO and AOKI, 1960; KAWANO et al., 1961). MASUDA and AOKI (1979), using mainly trace elements, showed that the calc-alkalic suite has higher Mg, K, Co, Cr, Ni, Th, and U than the tholeiitic suite, and also that each suite had a separate fractional crystallization. A model is presented here which is intended to explain both the mineralogical and chemical differences. KUNO's idea of assimilation is considered from a different point of view; that is, calc-alkalic basaltic andesite is formed by the partial assimilation of mafic rather than granitic material by a silicic tholeiitic andesite. Changes in the chemistry, mainly in the Mg/Fe ratio in the contaminated magma, prevents the crystallization of pigeonite; a drop in temperature as KUNO suggested is not as important although lower temperatures will help. It is demonstrated how such elements as K, Th, and U, which tend to be concentrated in granitic material, can be increased in the calc-alkalic rocks by addition of mafic xenoliths. This process is offered as an alternative to magma mixing, since it is believed that the mineralogical features used to support magma mixing could be explained equally well by assimilation.

Recent atmospheric injections of nuclear debris: Fallout from the 16 october 1980 nuclear explosion.

Abstract: The concentrations of 89Sr and 90Sr in a total of 117 samples of individual rain and snow collected at Fayetteville (36°N, 94°W), Arkansas, were determined radiochemically during the period between September 1979 and August 1981. A spectacular increase in the concentration of 90Sr in the atmospheric precipitation was observed during the month of March 1981, approximately 5 months after the 25th Chinese nuclear test of 16 Octuber 1980. A complicated pattern of variation of the 89Sr/90Sr ratio in rain observed after this nuclear explosion is interpreted in terms of the general theory of radioactive fallout based on the two-compartment model of the atmosphere, taking into consideration the fact that the nuclear debris released into the atmosphere at Lop Nor (40°N, 90°E), China, is known to travel eastward and circle the world more than once.

Nitrogen in stone meteorites and terrestrial standards

Abstract: Nitrogen contents have been determined by neutron activation method in stone meteorites and silicate standards. Leaching and sieving experiments on standards indicate that contamination from atmospheric nitrogen is negligible. For BCR-1 nitrogen contents show a range from 15 to 62ppm. The study includes 32 chondrites belonging to various classes and six achondrites. Nitrogen is high in C1 and C2 chondrites (500 to 1,000ppm) and in E chondrites (100 - 500ppm). C3 group shows variable amounts of nitrogen. Ordinary chondrites have similar nitrogen contents (~30pm) irrespective of their petrologic group. For all classes of meteorites, chondrules have lower nitrogen compared to the matrix. Dark phases of some gas- rich meteorites are enriched in nitrogen as compared to their light counterparts. Non-magnetic portions have slightly excess N compared to the magnetic portions. Correlation of N with C, In, Bi, Tl, Zn and Cd indicates the presence of two host phases for N.

Record of lead pollution in sediments of the Tokyo Bay, Japan

Abstract: Lead concentration and 210Pb activity profiles of 8 core samples from the inner Tokyo Bay were determined. The lead profiles showed a typical lead pollution pattern by human activities. Generally the lead concentration increased gradually from the background level of about 15 ppm before 1900 A.D. to the level in 1940's and then grew up rapidly until 1970. The pollution lead went up as high as about 7 times the natural value in around 1970 in some cores. Since 1970, lead concentration has been decreasing clearly up to date. The average lead accumulation rates in the bay were estimated to be 7.1μg/cm2/y in 1980 and 13μg/cm2/y in 1970. The value of 2.2μg/cm2/y in around 1880 seems close to the natural input rate. More than 75% of the accumulated lead during 1945–1980 was contributed by the pollution lead. Even before that time, 1900–1945, a half of the accumulated lead resulted from the human activities. The values indicate that the Tokyo Bay has been exposed to severe lead pollution for a long time.

The dissolution of lithium minerals in salt solutions: Implication for the lithium content of saline waters

Abstract: Lithium minerals, petalite (Li[AlSi4O10]) and lepidolite (K2(Li, Al)5-6[Si6-7Al2-1O20](OH, F)4), were reacted with seawater and NaCl solutions for 240 hours at 150 to 250°C and with a water/mineral ratio of 25 by weight, to clarify the role of dissolved salts on the enrichment of lithium in natural saline waters such as coastal thermal waters and fossil seawaters Lithium leaching from the minerals was enhanced with increasing salt concentration and temperature It was proved from the experiments using various salt solutions that NaCl solution and seawater are effective for the leaching of lithium from rocks and that even the altered seawaters containing low magnesium have the ability to extract lithium from rocks This investigation suggests that the non-volcanic saline waters of high lithium content (eg fossil seawater) can be produced by a long term seawater-rock interaction at relatively low temperature without a contribution from the so-called “magmatic emanation”

Apparent penetration of fallout 137Cs into rocks in Izu-Oshima.

Abstract: The distribution of 137Cs in volcanic rocks was measured for sliced samples of solid lava blocks from Izu-Oshima island, Japan. The decrease in 137Cs concentration with the increase in depth, together with the uneven spatial distribution, suggested that the fallout was responsible for the occurrence of 137Cs and that 137Cs might have penetrated into lavas as deep as several centimeters.

Geochemistry of Precambrian phosphate-carbonate intrusives from Bahia (Brazil)

Abstract: Pegmatoid bodies predominantly consisting of calcite and apatite occur associated with metasediments within Precambrian high-grade metamorphic basement rocks in the Fazenda das Panelas area, central Bahia State, Brazil. Petrology, trace elements, stable and radiogenic isotope chemistry of the carbonate-phosphate intrusives have been studied in order to clarify their genesis. K-Ar data give approximately 2.0b.y. that is likely to coincide with the metamorphic recrystallization of the basement rocks which occurred during the Transamazonic tectonic event. Rb-Sr data give somewhat older ages. C and O isotope data on the intrusive carbonates are distributed within the values of marine carbonates of Precambrian ages. Trace element chemistry and REE patterns in mineral phases (calcite, apatite, micas) give intermediate figures between sedimentary marine and igneous (carbonatitic) materials. The pegmatoids are supposed to have derived from the crystallization of carbonate-phosphate liquids formed by partial melting of phosphate-rich layers contained in the sedimentary sequence. The enrichment in REE and in large charged elements is explained by interaction of the phosphate-carbonate liquid with fluids of metamorphic origin. A possible paleoenvironmental characterization of the source phosphate rocks is presented.