The silicon isotopic composition of surface waters in the Atlantic and Indian sectors of the Southern Ocean

We report here the silicon isotopic composition (δ³⁰Si) of dissolved silicon (DSi) from 42 surface water samples from the Drake Passage, the Weddell Gyre, other areas south of the Southern Boundary of the Antarctic Circumpolar Current (ACC), and the ACC near the Kerguelen Plateau, taken between the beginning of February and the end of March 2007. From the beginning to end of the cruise (ANTXXIII/9), DSi diminished in the Antarctic by 50 μmol L⁻¹ while concentrations of nitrate + nitrite and phosphate showed no net decline, indicating that the high seasonal Si/N removal ratios well known for the Southern Ocean may be more related to the strength of the silicate pump in the Southern Ocean than to the instantaneous Si/N uptake ratio of diatoms. The δ³⁰Si of DSi in samples containing more than 20 μM DSi were strongly negatively correlated to DSi concentrations, supporting the use of δ³⁰Si as a proxy for DSi removal. The “open system” fractionation observed, ε = −1.2 ± 0.11‰, agrees well with results from previous work in other areas, and the estimate of the initial δ³⁰Si of DSi of +1.4‰ is not far off observations of the δ³⁰Si of DSi in Winter Water (WW) in this area. Results were used to model DSi draw down in the past from the δ³⁰Si of sediment cores, although isotopic fractionation during silica dissolution appeared to influence the δ³⁰Si of some surface water samples, inviting further study of this phenomenon.     

The temporal stability in lead isotopic signatures at selected sites in the Southern and Northern Hemispheres

A recent survey by [Bollh?fer and Rosman 2000] and [Bollh?fer and Rosman 2001] has defined the extent to which Pb isotopic ratios in aerosols vary on a global scale. However, it is also important for some applications to know how stable these signatures are. Here we report time series from 38 sites distributed worldwide in which aerosols have been sampled for periods of between 4 months and 4 yr. Apart from a few sites that have atypical conditions, European sites exhibit variations of <0.6% in the ²⁰⁶Pb/²⁰⁷Pb ratio. There is, however, evidence of seasonal variations at sampling sites closer to Eastern Europe that probably reflect an enhanced westward transport of pollution in winter. The variability in Canada and the United States is now larger than before due to a decrease of airborne Pb levels coupled with an increase in the variety of industrial sources. The temporal changes observed in the United States do not exhibit a seasonal pattern. One site in Winnipeg, Canada, showed an extremely large variation, probably the result of seasonal changes influencing the direction of movement of local smelting emissions. Temporal variations in mainland Australia are comparatively small, with a typical range of 0.2% in the ²⁰⁶Pb/²⁰⁷Pb ratio and isotopic ratios that indicate leaded petrol was still a major source of atmospheric Pb over the sampling period.     

Rare elements and Nd and Sr isotopic composition in micronodules from the Brazil Basin,Atlantic Ocean

The Sr isotope stratigraphy of the biogenic apatite was used to determine the age of pelagic sediments in the Brazil Basin (Station 1541) that contain ferromanganese micronodules, nodules, and coatings on the weathered volcanic rocks. The age of sediments at horizons 0–5 and 86–90 cm was estimated at 24.1 ± 0.2 Ma and 24.8 ± 0.2 Ma, respectively. The average sedimentation rate in the Late Oligocene was about 13 mm/ka. The hydrogenous Fe–Mn nodule on the sediment surface with the Mn/Fe value of 1.05–1.95 was formed at a rate of 1.2–2.4 mm/Ma, which is 1000 times lower than the growth rate of buried nodule (Mn/Fe 0.4) at depth of 83 cm. Diagenesis provoked changes in the mineral composition of the buried nodule (asbolane-buserite partially replaced by goethite), leading to the loss of a part of Mn, Ni, Li, and Tl but accumulation of trace elements linked with iron oxyhydroxides (Ce, Th, Be, As, and V) were retained. The composition of manganese micronodules at two studied depths in sediments evolved in the course of two stages of ore formation: related to the oxic and suboxic diagenesis. The Sr isotopic composition in manganese micronodules from both horizons do not differ from that of dissolved Sr in the ocean water. The ¹⁴³Nd/¹⁴⁴Nd ratio, which reflects the Nd isotopic composition in the paleocean during the micronodule formation, varies in manganese micronodules from different horizons and is constant in different size fractions.     

Galena mineralization in the Orcadian Basin,Scotland: Geological and isotopic evidence for sources of lead

Galena and other sulphides are widespread in the Old Red Sandstone (Devonian) Orcadian Basin. Syndiagenetic occurrences are associated with organic-rich sedimentary rocks, especially algal limestones. Epigenetic galenas are often spatially related to these syndiagenetic occurrences, particularly in the vicinity of Permo-Carboniferous igneous intrusions. Mineralization is concentrated about the granite-gneiss basement inlier in southwest Orkney.Orcadian Basin galenas have lead isotope compositions which show a linear trend related to Lewisian granulite facies metamorphism at about 2,700 Ma. The most radiogenic leads must include a component of average orogene or upper crustal lead. The isotopic compositions are notably similar to those of Caledonian granite feldspar leads measured by Blaxland et al. (1979). Granite was probably a source for lead in galena deposits about the basement in south-west Orkney, but away from the basement an average orogene component would have become increasingly important. There was no major input of magmatic lead to the basin during Permo-Carboniferous times, only a remobilization of existing lead.     

云南富宁者桑金矿床硫铅同位素地球化学特征与成矿物质来源

者桑金矿床赋存于上二叠统吴家坪组沉积碎屑岩中,矿体受构造破碎带控制,呈似层状、透镜状产出,是滇东南金成矿带上一个典型的卡林型金矿床。硫铅同位素地球化学研究显示,沉积黄铁矿和热液硫化物(黄铁矿和毒砂)的δ34S值均为正值,变化范围较窄(8.4‰～11.3‰),与二叠纪沉积时期海水硫酸盐δ34S值一致,具有地层硫的特征。矿石中的硫主要通过地层中有机质与海水硫酸盐的热还原作用(TSR)提供。铅同位素组成中,206Pb/204Pb变化范围较宽,207Pb/204Pb和208 Pb/204 Pb较为稳定,计算获得的模式年龄变化范围大(-62～389Ma),甚至出现"负年龄",表明除正常铅外,还有较多的放射性成因铅的混入。铅主要来自于上地壳,有少量岩浆物质的混入。矿石与围岩的硫铅同位素具有一定的继承性,成矿物质主要来自地层。     

Metallogeny and lead isotopic composition of base metal sulfide deposits in the Rappen area,northern Sweden

Early Proterozoic volcanic and sedimentary rocks of the Rappen district in northern Sweden were deposited at a destructive plate margin to the south of the Archaean craton of the western Baltic Shield. The volcano-sedimentary suite was intruded by two generations of early Proterozoic granites at ca. 1.89–1.85 Ga and ca.1.82–1.78 Ga, respectively, and metamorphosed at upper amphibolite facies conditions. Small stratabound iron, copper, and zinc deposits occur in felsic to mafic tuffs and arkosic sediments. Small deposits of molybdenum, tungsten, and uranium formed during the emplacement of the younger granites. The lead isotopic compositions of sulfide trace lead from the various deposits are highly heterogeneous. In the ²⁰⁶Pb/²⁰⁴Pb–²⁰⁷Pb/²⁰⁴Pb diagram they fall on mixing arrays between little evolved early Proterozoic lead and highly radiogenic Caledonian lead. The least radiogenic lead isotopic compositions from the various deposits have a wide range of ²⁰⁷Pb/²⁰⁴Pb ratios and thus indicate variable involvement of Archaean crustal lead in the Proterozoic deposits. Deposits hosted by siliciclastic rocks have higher ²⁰⁷Pb/²⁰⁴Pb ratios than deposits hosted in mafic to felsic tuffites. The lead isotopic heterogeneity suggests that the lead in the various deposits was locally derived and, furthermore, that the sedimentary rocks in part originated from the Archaean craton to the north. Lead mixing arrays in the ²⁰⁶Pb/²⁰⁴Pb–²⁰⁷Pb/²⁰⁴Pb diagram demonstrate that in Paleozoic time radiogenic lead was mobilized and transported in the basement. Source ages calculated from the mixing arrays (ca.1.9 Ga and ca.1.8 Ga) correspond to the age of the Early Proterozoic volcanism and metamorphism respectively. One group of deposits includes lead from at least three sources and illustrates that radiogenic lead was multiply mobilized and transported in the Proterozoic basement. It occurs in deposits that occur in zones that became permeable during the reactivations of the basement.     

Lead isotopic composition and lead source of the Tongchanghe basalt-type native copper-chalcocite deposit in Ninglang, western Yunnan, China

1 Introduction The native copper-chalcocite deposits associated with the Emeishan basalt have attracted great attention of many scientists engaged in ore deposits in recent years, but their focus is more put on the deposits hos- ted in the high-Ti basalt …     

The concentration and isotopic composition of carbon in basaltic glasses from the Juan de Fuca Ridge, Pacific Ocean

The abundance and 13C/12C ratios of carbon were analyzed in basaltic glass from twenty locations along the Juan de Fuca Ridge using a 3-step combustion/extraction technique. Carbon released during the first two combustion steps at 400-500 degrees C and 600-650 degrees C is interpreted to be secondary, and only the carbon recovered during a final combustion step at approximately 1200 degrees C is thought to be indigenous to the samples. For carbon released at approximately 1200 degrees C, glasses analyzed as 1-2 mm chips contained 23-146 ppm C with delta 13C values of -4.8 to -9.3%, whereas samples crushed to 38-63 microns or 63-90 microns yielded 56-103 ppm C with delta 13C values of -6.1 to -9.2%. The concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean-ridge basalts. The Juan de Fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor. Evidence of disequilibrium includes (1) a large range of carbon contents among glasses collected at similar depths, (2) a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample, and (3) a lack of correlation between vesicle abundance, carbon concentration, and depth of eruption. Variations in carbon concentration and delta 13C ratios along the ridge do not correlate with major element chemistry. The observed relationship between carbon concentrations and delta 13C values may be explained by late-stage, variable degrees of open-system (Rayleigh-like) degassing.     

Lead isotopic composition from data of high-precession MC-ICP-MS and sources of matter in the large-scale Sukhoi Log noble metal deposit,Russia

The lead isotopic composition of 33 sulfide samples from orebodies of the Sukhoi Log deposit was studied by high-precession MC-ICP-MS with a precision of ±0.02% (±2SD from 120 analyses of the SRM 981 standard sample). The deposit is located in the Bodaibo gold mining district in the northern Baikal-Patom Highland. Gold mineralization is hosted in Neoproterosoic black slates. Variations of lead isotope ratios of the Sukhoi Log sulfides are generally typical of Phanerozoic deposits and ore fields. They are significant for ²⁰⁶Pb/²⁰⁴Pb (17.903–18.674), moderate for ²⁰⁸Pb/²⁰⁴Pb (37.822–38.457), and relatively narrow for ²⁰⁷Pb/²⁰⁴Pb (15.555–15.679). In the Pb-Pb isotope diagrams, the data points of pyrite and galena constitute a linear trend. The points corresponding to pyrite from metasomatic ore occupy the left lower part of the trend. Galena from late gold-quartz veins shows more radiogenic Pb, and corresponding data points are located in the upper part of the trend. According to the Stacey-Kramers model, the end points of the trend, which is regarded as a mixing line, have μ₂ = 9.6 and μ₂ = 13.2 and model Pb-Pb ages 455 and 130 Ma, respectively. The isotope characteristics of ore lead, their relationships in pyrite and galena, and the mixing trend of Pb isotopic compositions are clearly tied to two Paleozoic stages in the formation of the Sukhoi Log deposit (447 ± 6 and 321 ± 14Ma) and testify to the leading role of crustal sources, which are suggested as being the Neoproterozoic black-shale terrigenous-carbonate rocks.     

Variations in composition and abundance of white mica in the hydrothermal alteration system at Hellyer,Tasmania, as revealed by infrared reflectance spectroscopy

Short-wave infrared (SWIR) spectral reflectance of hydrothermally altered volcanic rocks in the footwall of the Hellyer massive sulfide deposit was measured with a portable PIMA-II infrared spectrometer. The Al–OH band was used to derive information on the octahedral Al content and the abundance of white mica (sericite) in the hydrothermal alteration and mineralization system. The range of the Al–OH band wavelength from 2192 nm to 2222 nm corresponds to the number of octahedral Al (Al^vi) in white mica approximately from 3.9 to 3.0 (based on 4 octahedral cations per formula). This Al^vi range represents a significant compositional variation, covering most of the compositional region between muscovite (Al^vi = 4.0) and phengite (Al^vi = 3.0). Furthermore, the spectral reflectance data show that the compositional variation of white mica is spatially related to hydrothermal alteration zoning, such that phengitic white mica tends to occur in 1) main upflow fluid channel, 2) intensely altered volcanic rocks, and 3) Pb–Zn mineralization, whereas muscovitic white mica was formed preferentially distal to massive sulfide mineralization on the margin of the footwall alteration system. The results suggest that the Al–OH band wavelength, and therefore the octahedral Al content, of white mica can be used as vectors to mineralization to map the hydrothermal system at Hellyer.     

西藏拿若铜（金）矿床硫、铅同位素组成及成矿物质来源

为探讨多龙矿集区拿若铜（金）矿床的成矿物质来源,研究矿床成矿机制,本文在详细的野外地质调查和矿石学研究基础上对矿石样品进行硫和铅同位素分析,并对成因意义进行讨论。研究结果表明,17件金属硫化物的δ³⁴S值变化于－2.3‰~2.3‰之间,均值为－0.1‰;其中13件黄铁矿δ³⁴S值变化范围为－2.3‰~2.3‰,均值为0.2‰;4件黄铜矿的δ³⁴S值变化范围为－1.5~－0.8‰,均值为－1.1‰。δ³⁴S值频率直方图总体具有塔式分布特征,平均值接近于零,具幔源硫特征。金属硫化物的²⁰⁸Pb/²⁰⁴Pb介于38.209~38.854之间,平均值为38.635;²⁰⁷Pb/²⁰⁴Pb变化范围为15.541~15.665,平均值为15.605;²⁰⁶Pb/²⁰⁴Pb为17.942~18.580,平均值为18.461,具有正常铅的特征。铅同位素μ值变化范围为9.40~9.57,均小于9.58,表明矿床铅主要来自幔源物质。拿若矿床的硫和铅同位素特征与多龙矿集区斑岩型矿床类似,成矿物质主要来源于岛弧环境下幔源物质,可能存在壳源物质的混入。

     

Changes in ionic and oxygen isotopic composition of the snow-firn pack at Baishui Glacier No. 1, southeastern Tibetan Plateau

To properly interpret climatic and environmental information recorded in ice cores retrieved in the temperate-glacier region, the post-depositional processes, especially the meltwater percolation, need to be well understood. From late April to mid-July 2006, two successive snow pits, site P1 located at 4,750?m a.s.l. in the ablation zone and site P2 at 4,900?m a.s.l. in the accumulation area at Baishui Glacier No. 1, Mt. Yulong, southeastern Tibetan Plateau, were excavated. Changes in soluble ions (K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^?, NO₃ ^? and SO₄ ^2?) and stable oxygen isotopes (??¹⁸O) in the snow pits were investigated. Before the melting period, soluble ions and ??¹⁸O exhibit pronounced seasonal variations, with high values in the upper snow-firn layer (accumulated in winter/spring season) and relatively low values in the lower firn layer (deposited in summer season), reflecting seasonal shift in the Indian summer monsoon and winter westerlies over the region. During the melting period, most ions in the upper snow-firn layer were leached with different efficiencies. Although no significant changes in ion concentrations in the lower firn layer were observed, the impurities in the upper snow-firn layer could be eluted down into the lower firn layer. However, the pre-melting isotopic stratigraphy remained relatively unchanged during the observation period, indicating that the influence of meltwater percolation on stable isotopes is less significant than that on soluble ions. This understanding is crucial for the interpretation of ice-core records in the monsoon temperate-glacier region.     

Late Quaternary glaciation in Southern Africa: moraine ridges and glacial deposits at Mount Enterprise in the Drakensberg of the Eastern Cape Province,South Africa

Late Quaternary moraines and diamictons containing striated clasts are described from near Elliot in the Drakensberg of South Africa. An equilibrium line altitude (ELA) of 2109 m is suggested for the palaeoglacier associated with the innermost moraine. This glacier was fed by a very extensive snowblow area and the ELA may reflect the temperature–precipitation–wind ELA rather than the temperature–precipitation ELA and be considerably below the ‘regional’ ELA. Mean annual air temperatures when glaciation occurred were probably at least 10.0°C below those of the present. Copyright © 2001 John Wiley & Sons, Ltd.     

西藏多龙矿集区地堡Cu(Au)矿床含矿斑岩锆石U-Pb测年、Hf同位素组成及其地质意义

西藏多龙矿集区地堡铜(金)矿位于班公湖—怒江缝合带北侧,羌塘地块南缘,是多龙矿集区中具有较好找矿前景的斑岩—浅成低温热液矿床。本文首次对地堡含矿斑岩进行LA-ICP-MS锆石U-Pb测年、微量元素和Hf同位素分析。含矿斑岩23个锆石点测试,获得锆石~(206)Pb/~(238)U加权平均值年龄为122.0±2.5Ma(MSWD=0.34),与多龙矿集区成矿岩浆活动时限一致,是多龙矿集区的重要组成部分。锆石微量元素特征揭示地堡含矿斑岩中锆石为岩浆锆石,锆石Ti温度计计算出其结晶温度为663~850℃,平均为765℃,其岩浆源区可能经历了水饱和条件下的部分熔融作用。Hf同位素分析结果表明,地堡含矿斑岩锆石n(~(176)Hf)/n(~(177)Hf)值相对较高,为0.282726~0.283054,ε_(Hf)(t)为1.1~12.6,均为正值,其物质来源有幔源组分的加入,可能为壳幔混源的新生下地壳。     

Heavy metal concentrations and Pb isotopic composition in urban and suburban aerosols of Hong Kong and Guangzhou, South China-Evidence of the long-range transport of air contaminants

Rapid urbanization and industrialization in South China has placed a great strain on the environment and human health. In the present study, the total suspended particulate matter （TSP） in the urban and suburban areas of Hong Kong and Guangzhou, the two largest urban centres in South China, was sampled from December 2003 to January 2005. The samples were analyzed for their concentrations of major elements （Al, Fe, Mg and Mn） and trace metals （Cd, Cr, Cu, Pb, V and Zn）, and for Pb isotopic composition. Elevated concentrations of metals, especially Cd, Pb, V and Zn, were observed in the urban and suburban areas of Guangzhou, showing significant atmospheric trace element pollution. Distinct seasonal patterns were observed in the heavy metal concentrations of aerosols in Hong Kong, with higher metal concentrations during the winter monsoon period, and lower concentrations during summer time. The seasonal variations in metal concentrations of the aerosols of Guangzhou were less distinct, suggesting the dominance of local sources of pollution around the city. The Pb isotopic composition in the aerosols of Hong Kong had higher ^206Pb/^207Pb and ^208Pb/^207Pb ratios in winter, showing the influence of Pb from the northern inland areas of China and the Pearl River Delta （PRD） region, and lower ^206Pb/^207Pb and ^208Pb/^207Pb ratios in summer, indicating the influence of Pb from the South Asian region and from marine sources.     

Sr and Sr/Sr in the Yamuna River System in the Himalaya: sources, fluxes, and controls on sr isotope composition

Sr and ⁸⁷Sr/⁸⁶Sr have been measured in the Yamuna river headwaters and many of its tributaries (YRS) in the Himalaya. These results, with those available for major ions in YRS rivers and in various lithologies of their basin, have been used to determine their contributions to riverine Sr and its isotopic budget. Sr in the YRS ranges from 120 to 13,400 nM, and ⁸⁷Sr/⁸⁶Sr from 0.7142 to 0.7932. Streams in the upper reaches, draining predominantly silicates, have low Sr and high ⁸⁷Sr/⁸⁶Sr whereas those draining the lower reaches exhibit the opposite resulting from differences in drainage lithology. ⁸⁷Sr/⁸⁶Sr shows significant co-variation with SiO₂/TDS and (Na^* + K)/TZ⁺ (indices of silicate weathering) in YRS waters, suggesting the dominant role of silicate weathering in contributing to high radiogenic Sr. This is also consistent with the observation that streams draining largely silicate terrains have the highest ⁸⁷Sr/⁸⁶Sr, analogous to that reported for the Ganga headwaters. Evaluation of the significance of other sources such as calc-silicates and trace calcites in regulating Sr budget of these rivers and their high ⁸⁷Sr/⁸⁶Sr needs detailed work on their Sr and ⁸⁷Sr/⁸⁶Sr. Preliminary calculations, however, indicate that they can be a significant source to some of the rivers.It is estimated that on an average, ∼25% of Sr in the YRS is derived from silicate weathering. In the lower reaches, the streams receive ∼15% of their Sr from carbonate weathering whereas in the upper reaches, calc-silicates can contribute significantly (∼50%) to the Sr budget of rivers. These calculations reveal the need for additional sources for rivers in the lower reaches to balance their Sr budget. Evaporites and phosphorites are potential candidates as judged from their occurrence in the drainage basin. In general, Precambrian carbonates, evaporites, and phosphorites “dilute” the high ⁸⁷Sr/⁸⁶Sr supplied by silicates, thus making Sr isotope distribution in YRS an overall two end member mixing. Major constraints in quantifying contributions of Sr and ⁸⁷Sr/⁸⁶Sr from different sources to YRS rivers are the wide range in Sr and ⁸⁷Sr/⁸⁶Sr of major lithologies, limited data on Sr and ⁸⁷Sr/⁸⁶Sr in minor phases and on the behavior of Sr, Na, and Ca during weathering and transport.The Ganga and the Yamuna together transport ∼0.1% of the global Sr flux at the foothills of the Himalaya which is in the same proportion as their contribution to global water discharge. Dissolved Sr flux from the Yamuna and its mobilization rate in the YRS basin is higher than those in the Ganga basin in the Himalaya, a result consistent with higher physical and chemical erosion rates in the YRS.     

Lipid composition of the pelagic crab Pleuroncodes planipes, its feces, and sinking particulate organic matter in the Equatorial North Pacific Ocean

Fecal pellets from the pelagic crab Pleuroncodes planipes were a substantial portion of the particulate organic matter in a sediment trap deployed at the bottom of the mixed layer in the eastern tropical North Pacific Ocean. The lipids of fresh P. planipes feces were compared to lipids of the sediment trap material, of mixed zooplankton which may comprise part of the diet of the crab, and of the crab itself in order to elucidate the source of organic compounds found in the trap. Hydrocarbons, wax esters, triacylglycerols, steroidal alcohols, steroidal ketones, and fatty acids were determined by capillary gas chromatography and gas chromatography/mass spectrometry. Significant input of lipids via sedimentation of crab fecal material is indicated, and modification of dietary lipid within the gut of the crab is inferred. Labile dietary fatty acids are depleted and sterols enriched in the fecal pellets and trap material relative to the zooplankton and crab. Nuclear saturated and unsaturated 3-ketosteroids and unsaturated steroidal hydrocarbons were detected in the crab, its feces, and in the sediment trap particulate material.     

Stable isotopic composition of soil calcite (O,C) and gypsum (S) overlying Cu deposits in the Atacama Desert,Chile: Implications for mineral exploration,salt sources,and paleoenvironmental reconstruction

Soils overlying two porphyry Cu deposits (Spence, Gaby Sur) and the Pampa del Tamarugal, Atacama Desert, Northern Chile were collected in order to investigate the extent to which saline groundwaters influence “soil” chemistry in regions with thick Miocene and younger sediment cover. Soil carbonate (calcite) was analyzed for C and O isotopes and pedogenic gypsum for S isotopes. Soil calcite is present in all soils at the Spence deposit, but increases volumetrically above two fracture zones that cut the Miocene gravels, including gravels that overlie the deposit. The C isotope composition of carbonate from the soils overlying fracture zones is indistinguishable from pedogenic carbonate elsewhere at the Spence deposit; all δ¹³C_VPDB values fall within a narrow range (1.40–4.23‰), consistent with the carbonate having formed in equilibrium with atmospheric CO₂. However, δ¹⁸O_VPDB for carbonate over both fracture zones is statistically different from carbonate elsewhere (average δ¹⁸O_VPDB = 0.82‰ vs. −2.23‰, respectively), suggesting involvement of groundwater in their formation. The composition of soils at the Tamarugal anomaly has been most strongly affected by earthquake-related surface flooding and evaporation of groundwater; δ¹³C_VPDB values (−4.28‰ to −2.04‰) are interpreted to be a mixture of dissolved inorganic C (DIC) from groundwater and atmospheric CO₂. At the Spence deposit, soils only rarely contain sufficient SO₄ for S isotope analysis; the SO₄-bearing soils occur only above the fracture zones in the gravel. Results are uniform (3.7–4.9‰ δ³⁴S_CDT), which is near the middle of the range for SO₄ in groundwater (0.9–7.3‰). Sulfur in soils at the Gaby Sur deposit (3.8–6.1‰ δ³⁴S_CDT) is dominated by gypsum, which primarily occurs on the flanks and tops of hills, suggesting deposition from SO₄-rich fogs. Sulfate in Gaby Sur deposit gypsum is possibly derived by condensation of airborne SO₄ from volcanic SO₂ from the nearby Andes. At the Gaby Sur deposit and Tamarugal anomaly, pedogenic stable isotopes cannot distinguish between S from porphyry or redeposited SO₄ from interior salars.The three sites studied have had different histories of salt accumulation and display variable influence of groundwater, which is interpreted to have been forced to the surface during earthquakes. The clear accumulation of salts associated with fractures at the Spence deposit, and shifts in the isotopic composition of carbonate and sulfate in the fractures despite clear evidence of relatively recent removal of salts indicates that transfer from groundwater is an ongoing process. The interpretation that groundwaters can influence the isotopic composition of pedogenic calcrete and gypsum has important implications for previous studies that have not considered this mechanism.     

Rb,Sr and strontium isotopic composition,K/Ar age and large ion lithophile trace element abundances in rocks and glasses from the Wanapitei Lake impact structure

Shock metamorphosed rocks and shock-produced melt glasses from the Wanapitei Lake impact structure have been examined petrographically and by electron microprobe. Eleven clasts exhibiting varying degrees of shock metamorphism and eight impact-produced glasses have been analyzed for Rb, Sr and Sr isotopic composition. Five clasts and one glass have also been analyzed for large ion lithophile (LIL) trace element abundances including Li, Rb, Sr, and Ba and the REE's.The impact event forming the Wanapitei Lake structure occurred 37 m.y. ago based on K/Ar dating of glass and glassy whole-rock samples. Rb/Sr isotopic dating failed to provide a meaningful whole-rock or internal isochron. The isotopic composition of the glasses can be explained by impact-produced mixing and melting of metasediments. Large ion lithophile trace element abundance patterns confirm the origin of the glasses by total shock melting of metasediments.