Radiocarbon redating of contaminated samples from a tropical volcano: the Mansion ‘Series’ of St Kitts,West Indies

Heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits, in addition to easy contamination of this wood by root systems and soluble humic material. Because the physical nature of the charcoal varies, some samples are more prone to contamination. Two independent studies of the same volcano, Mt Liamuiga on St Kitts in the Lesser Antilles, sometimes using samples from the same carbonized tree, yielded a systematic difference in radiocarbon ages. An exchange of samples and a re-investigation of three physically distinct types of charcoal yielded the following results. Rare, hard, dense charcoal, lacking contamination, which had yielded a spurious age of 2860 years bp, was redated at 1845±58 years bp. Common soft, friable charcoal with good cellular structure proved to be susceptible to contamination. A field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre-treatment was used, indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets. A previous date of 24870 years bp obtained from powdery charcoal in a horizon beneath the Mansion Series contradicted ages older than 41000 years bp from common friable charcoal in the lower Mansion Series. The soft powdery charcoal was re-investigated using a sample collected a few centimeters from the original, although field decontamination of this sample was not possible, more extensive laboratory treatment yielded an age of ca. 43000 years bp, again proving that routine laboratory pretreatments are inadequate. A revised geochronology for the Mansion Series is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits.     

Dynamics of the plasmasphere in the dusk sector as observed in the outer ionosphere

Summary Direct measurements of the thermal plasma parameters in the topside ionosphere reveal variations of the plasmasphere boundary in the dusk sector. The ACTIVE satellite's near-polar orbits at altitudes of 500 – 1800 km around winter solstice 1989 were used to study the bulge region of the plasmasphere during intervals with different levels of geomagnetic agitation. The narrow, sharply defined trough in electron concentration corresponding to the plasmapause under quiet conditions situated at L = 6 – 7 moved to lower L-values with increasing geomagnetic activity. This narrow trough can be found in all main ion constituents. During periods of moderate geomagnetic activity, following the onset of a weak magnetic storm, a portion of the plasmaspheric bulge region was separated from the main plasmaspheric body. This can be seen in the outer ionosphere as an inner narrow trough at lower L-value. Troughs in light ions need no longer coincide with this in electron concentration. He⁺ is the most sensitive constituent reflecting the dusk sector plasmaspheric situation at this altitude.Dedicated to the Memory of Professor Karel P     

Blind prediction of the site effects at Ashigara Valley,Japan, and its comparison with reality

Weak and strong ground motions were numerically predicted for three stations of the Ashigara Valley test site. The prediction was based on the records from a rock-outcrop station, one weak-motion record from a surface-sediments station, and the standard geotechnical model. The data were provided by the Japanese Working Group on the Effects of Surface Geology as a part of an international experiment. The finite-difference method for SH waves in a 2-D linear viscoelastic medium (a causalQ model) was employed.Comparison with the real records shows that at two stations the predictions fit better than at the third one. Strangely, the two better predictions were for stations situated at larger distances from the reference rock station (one station was on the surface, the other in a borehole). The strong ground motion (the peak acceleration of about 200 cm s^–2) was not predicted qualitatively worse than the weak motion (8 cm s^–2). A less sophisticated second prediction (not submitted during the experiment), in which we did not attempt to fit the available weak-motion record at the sedimentary station, agrees with the reality significantly better.     

Solubility of Pt and Pd sulfides and Au metal in aqueous bisulfide solutions

An experimental study of the solubility of Pt and Pd sulfides and Au metal in aqueous bisulfide solutions was conducted at temperatures from 200° to 350 °C and at saturated vapor pressure. A 500-mL Bridgemantype pressure vessel constructed of titanium, and equipped with a motor-driven magnetic stirrer was employed. The pH and the oxidation state were buffered by the coexistence of H₂S/HS^–/SO _inf4 ^sup2– . The pH at temperature was calculated to be in the range 5.91–9.43, and S was 0.3–2.2 m. Under the experimental conditions, the measured solubility of gold is about two to three orders of magnitude greater than that of either platinum and palladium, and the measured solubility of platinum is, in general, approximately equal to that of palladium, in molal units. The solubilities are found to be in the range: platinum 4–800 ppb, palladium 1–400 ppb, and gold 2–300 ppm. The solubility data can be modeled adequately using the following reactions: Au+H₂S+HH^–=Au(HS) ₂ ^– +1/2H₂ (K₁₄); PtS+HS^–+H⁺=Pt (HS) ₂ ⁰ (K₁₅); PdS+HS^–+H⁺=Pd (HS) ₂ ⁰ (K₁₆); PtS₂+H₂=Pt (HS) ₂ ⁰ (K₂₁).With equilibrium constants determined as follows (errors represent two standard deviations): Preliminary measurements of the solubilities of metallic Pt, Pd and Au as hydroxide complexes were also conducted using a second titanium pressure vessel, at temperatures of 200° to 350 °C and vapor saturation pressure, with pH and the oxidation state controlled or buffered by adding known amounts of NaOH and H₂ gas. The concentration of NaOH was in the range 0.01–1.3 m, and the partial pressure of H₂ at 200 °C was 62–275 bars, initially. Under the temperature and pressure conditions of these experiments, the solubility of platinum in 1 m NaOH solution is less than 100 ppb, that of palladium is less than 10 ppb and that of gold is less than 0.2 ppm; and in 0.01 m NaOH solutions, both Pt and Pd solubilities are less than 1 ppb. These data indicate that the contributions of hydroxide complexes to the total solubilities in the bisulfide runs, where the pH was in the range of 5.9–9.4, are negligible. The concentrations of both Pt and Pd as bisulfide complexes in the Salton Sea geothermal system predicted using the stability constants determined in this work agree very well with those values measured by McKibben et al. (1990). This calculation strongly suggests that the PGE are transported in moderately reducing, near neutral hydrothermal fluids as bisulfide complexes, as is gold. However, the much lower maximum solubility of the PGE relative to gold severely constrains models of re genesis, and may explain the relative rarity of hydrothermal PGE deposits compared to the relative abundance of hydrothermal Au deposits.     

Aqueous alteration of the Bali CV3 chondrite: evidence from mineralogy, mineral chemistry, and oxygen isotopic compositions

A petrographic, geochemical, and oxygen isotopic study of the Bali CV3 carbonaceous chondrite revealed that the meteorite has undergone extensive deformation and aqueous alteration on its parent body. Deformation textures are common and include flattened chondrules, a well-developed foliation, and the presence of distinctive (100) planar defects in olivine. The occurrence of alteration products associated with the planar defects indicates that the deformation features formed prior to the episode of aqueous alteration. The secondary minerals produced during the alteration event include well-crystallized Mg-rich saponite, framboidal magnetite, and Ca-phosphates. The alteration products are not homogeneously distributed throughout the meteorite, but occur in regions adjacent to relatively unaltered material, such as veins of altered material following the foliation. The alteration assemblage formed under oxidizing conditions at relatively low temperatures (<100 degrees C). Altered regions in Bali have higher Na, Ca, and P contents than unaltered regions which suggests that the fluid phase carried significant dissolved solids. Oxygen isotopic compositions for unaltered regions in Bali fall within the field for other CV3 whole-rocks, however, the oxygen isotopic compositions of the heavily altered material lie in the region for the CM and CR chondrites. The heavy-isotope enrichment of the altered regions in Bali suggest alteration conditions similar to those for the petrographic type-2 carbonaceous chondrites.     

Geomagnetic activity as a possible cause of changes in the middle atmosphere and troposphere; observations made in Prague in the years 1932–1987

Summary A possible relation between the 10-day, 1-month, and 2-month geomagnetic as well as solar activity, characterized by Kp and Wolf's number R, and temperatures measured at the Prague-Klementinum meteorological station in January–February of the years 1932–1987 was sought. It was found that:1) Kp correlates with the temperature in Prague better than Wolf's number R.2) If the QBO phase is taken into account, the correlations improve.3) Even if the correlations improves with increasing length of the subintervals into which the individual winter periods (January-February) were derived, their statistical significance declines.     

The shoshonite porphyry Cu-Au association in the Goonumbla District,N.S.W., Australia

Summary The Goonumbla porphyry copper-gold deposit in N.S.W., Australia, is hosted by late Ordovician (439.2 ± 1.2 Ma)shoshonitic igneous rocks. In terms of their petrography, the rocks vary from andesitic to dacitic lavas and tuffs which are partly intruded by monzonite stocks; they are characterized by high and variable Al₂O₃ (13.4–19.9 wt%), very high K₂O values (up to 6.8 wt%), and high K₂O/Na₂O ratios (0.58–1.48), which are typical for the shoshonite association. The rocks also have enriched LILE concentrations (Ba up to 1200 ppm, Sr up to 1350 ppm), low HFSE (TiO₂ < 0.67 wt%, Zr < 125 ppm, Nb < 10 ppm, Hf < 3.4 ppm), and very low LREE (La < 22.4 ppm, Ce < 31 ppm), which are typical for potassic volcanic rocks formed in alate oceanic-arc setting.Mineral chemistry of selected magmatic mica and apatite phenocrysts from host rocks reveals relatively high SrO and BaO contents (micas: 0.15 wt% and up to 0.28 wt%, respectively; apatites: up to 0.28 wt% and 0.19 wt%, respectively) and very high halogen concentrations. Micas are characterized by up to 3.9 wt% F and 0.14 wt% Cl, whereas apatites have up to 3.6 wt% F and 0.68 wt% Cl. These very high halogen contents compared to those from barren intrusions imply that the shoshonitic magmatism was the source of mineralization.Copper-gold mineralization consists mainly of bornite, chalcopyrite, chalcocite and minor pyrite and tetrahedrite. Native gold occurs mainly as minute grains within silicates of the host rocks, and more rarely as fine inclusions in the sulphides. Mineralization is accompanied by wallrock alteration comprising a spatially restricted potassic type and a regional propylitic alteration type.Thus, the porphyry copper-gold deposit in the Goonumbla district can be viewed as an additional example of a worldwide association between potassic/shoshonitic magmatism and base- and precious-metal mineralization. More specifically, it appears to be the oldest recorded example of a shoshontie-associated porphyry Cu-Au deposit from a late oceanic-arc setting, a possible modern analogue being Ladolam at Lihir Island, Papua New Guinea

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Die Shoshonit Porphyry Cu-Au Assoziation im Goonumbla Distrikt, N.S.W., Australien

Zusammenfassung Die Porphyry Cu-Au Vererzung im Goonumbla Distrikt in New South Wales, Australien, sitzt in oberordovizischen (ca. 439.2 ± 1.2 Ma) Shoshoniten auf. Das petrographische Spektrum dieser Gesteine reicht von andesitischen bis dazitischen Laven und Tuffen, die lokal von Monzonit-Stöcken intrudiert werden; die Gesteine besitzen hohe, aber variable Al₂O₃ Gehalte (13.4–19.9 Gew%), sehr hohe K₂O Gehalte (bis zu 6.8 Gew%) und hohe K₂O/Na₂O Verhältnisse (0.58–1.48), die typisch sind für Shoshonite. Außerdem weisen sie hohe Konzentrationen an LILE Elementen (Ba bis 1200 ppm, Sr bis 1350 ppm) auf und geringe Konzentrationen an HFSE (TiO₂ < 0.67 Gew%, Zr < 125 ppm, Nb < 10 ppm, Hf < 3.4 ppm) sowie an LREE (La < 22.4 ppm, Ce < 31 ppm), die als typisch gelten für potassische Vulkanite von ozeanischen Plattengrenzen.Die Mineralchemie von repräsentativen Glimmer- und Apatit-Phänokristallen ist charakterisiert durch hohe SrO und BaO Gehalte (Glimmer: 0.15 Gew%, bzw. bis 0.28 Gew%; Apatite: bis 0.28 Gew%, bzw. 0.19 Gew%). Sie enthalten ferner sehr hohe Halogen-Konzentrationen. Die Glimmer enthalten beispielsweise bis zu 3.9 Gew% F und 0.14 Gew% Cl, während Apatite bis zu 3.6 Gew% F und 0.68 Gew% Ci aufweisen. Dies erscheint nicht ungewöhnlich, weil Glimmer und Apatite von vererzten Mag matiten zumeist deutlich höhere Halogengehalte besitzen, als solche von unvererzten Magmatiten. Die hohen Halogen-Gehalte in Phänokristallen aus den Shoshoniten legen nahe, die Vulkanite als den Ursprung der Vererzung zu interpretieren.Die Cu-Au Vererzung besteht überwiegend aus den Sulfiden Bornit, Kupferkies, Kupferglanz und vereinzelt auftretendem Pyrit und Tetrahedrit. Gediegen Gold wird in der Regel nur als kleine Partikel innerhalb von Silikaten der shoshonitischen Wirtsgesteine und seltener als feine Einschlüsse in Sulfiden gefunden.Die Vererzung wird von hydrothermaler Alteration der Wirtsgesteine begleitet und zwei Alterationsarten lassen sich unterscheiden: eine potassische sowie eine regional zu beobachtende propylitische Alteration.Die Porphyry Cu-Au Lagerstätte im Goonumbla Gebiet ist ein Beispiel für die weltweit beobachtete Assoziation von Bunt- und Edelmetallvererzungen und potassisch/shoshonitischem Magmatismus. Der Goonumbla Distrikt stellt die älteste bisher bekannte Porphyry Cu-Au Lagerstätte aus einerspätgenetischen ozeanischen Plattengrenze dar. Einmodernes Beispiel für eine Cu-Au Lagerstätte vergleichbaren Typs ist Ladolam auf Lihir Island, Papua New Guinea.

     

Environmental geochemistry of the River Gomti: A tributary of the Ganges River

Water and sediment samples collected from the Gomti River, a tributary of the Ganges River system, during the postmonsoon season have been analyzed to estimate major elemental chemistry. Water chemistry of the River Gomti shows almost monotonous spatial distribution of various chemical species, especially because of uniform presence of alluvium Dun gravels throughout the basin. The river annually transports 0.34×10⁶ tonnes of total suspended material (TSM) and 3.0×10⁶ tonnes of total dissolved solids (TDS), 69 percent of which is accounted for by bicarbonate ions only. Samples collected downstream of the city of Lucknow show the influence of anthropogenic loadings for a considerable distance in the river water. Na⁺, Cl^–, and SO₄ ^2– concentrations build up downstream. The bed sediment chemistry is dominated by Si (36 percent), reflecting a high percentage of detrital quartz, which makes up about 74 percent of the mineralogy of the bed sediments in the River Gomti. The average Kjeldahl nitrogen concentration (234 g/g) indicates indirectly the amount of organic matter in the sediments. The Hg concentration in sediments has been found to be higher (average 904 ppb) than the background value. The suspended sediments are well sorted, very finely skewed, and extremely leptokurtic, indicating a low energy condition of flow in the Gomti River. The influence of chemical loads in the Gomti has been found to be small or nonexistent on the Ganges River, perhaps because the water discharge of the Gomti (1.57 percent) to the Ganges is quite low.     

Strömgren and Hβ photometry of OB stars in Serpens

Strömgren and H photometry of 25 stars in the field of Serpens are presented. The excesses, the absolute magnitude and the temperatures of the stars are obtained. The masses and the ages are also estimated.     

Long,accurate time series measurements of radial velocities of solar-type stars

We have been measuring changes in the radial velocities (RV's) of solar-type stars to search for gravitational perturbations by planets. We transmit violet starlight through a Fabry-Perot etalon interferometer and sense changes in Doppler shift from changes in the fluxes of light on the slopes of stellar absorption lines. Our data now span 6 years. Our observations of the Sun showed earlier that both our technique and the profiles of solar photospheric violet absorption lines can be stable enough to reveal planetary perturbations. We now carry this validation to the spectra of other near-solar-type stars. Annual averages of our RV's of Draconis and Virginis are stable to ±6 m s^–1. The slope of our five-year series of RV's of Bootis A is consistent with the star's well-determined visual astrometric orbit about Bootis B. The Fabry-Perot technique of Doppler shift measurement is fully capable of detecting perturbations due to planets with masses and orbits similar to those of Jupiter.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.