Trace Element Concentration Data Research Articles

Semi-quantitative μLIBS mapping of germanium diffusion between metal and silicate during planetary core–mantle segregation

Understanding the distribution of elements between the cores and mantles of planetary bodies is essential for elucidating the geological and geochemical processes operating during their formation. Because the semi-metallic element Ge shows complex siderophile, chalcophile, and lithophile properties, it is particularly significant for investigating core–mantle segregation and ore deposit formation. Recent advancements in in situ microanalysis techniques, such as μLIBS, have enabled high-resolution elemental mapping of Ge and other trace elements.This study explores the application of μLIBS imaging to investigate the high-temperature/high-pressure distribution of Ge between metallic and silicate matrices analogous to planetary cores and mantles. By cross-calibrating the μLIBS intensities with electron microprobe profile analyses carried out on piston cylinder experimental samples, we produced semi-quantitative Ge maps from which we extracted Ge concentration profiles to assess Ge diffusion from the silicate to the metal. We determined, for the first time, the diffusion coefficient of Ge between metal and silicate to be D(Ge)metal = 4.03E−13 ± 3.6E−14 m2/s at 1 GPa and 1350 °C. Our results demonstrate the capability and efficiency of μLIBS for providing detailed, high-resolution (15 μm) trace element concentration data at few ppm levels, offering a time- and cost-effective alternative to conventional techniques.These findings bring insights on planetesimal differentiation and on chemical exchanges between metal and silicate phases in a magma ocean and between two different metal phases occurring at the bottom of the magma ocean during planetesimal formation.

Nature and timing of Sn mineralization in southern Hunan, South China: Constraints from LA-ICP-MS cassiterite U-Pb geochronology and trace element composition

Abstract Accurately determining the timing and mechanism of metallogenesis of ore deposits is essential for developing a robust genetic model for their exploration. In this paper, we analyze the formation conditions of cassiterite in five major deposits of southern Hunan Province, one of the most important tungsten-tin (W-Sn) provinces in South China, using a combination of cathodoluminescence imaging, in situ U-Pb geochronology, and trace-element concentration data. In situ cassiterite U-Pb geochronology constrains the main period of Sn mineralization to between 155.4 and 142.0 Ma, demonstrating a temporal and genetic relationship to silicic intrusive magmatism in the same area. Three stages of magmatic activity and metallogenic evolution are recognized: (1) Early Paleozoic and Triassic: the initial enrichment stage of tungsten and tin; (2) Jurassic: the metasomatic mineralization stage; and (3) Cretaceous: the magmatic-hydrothermal superposition stage. The cassiterite in these deposits takes four forms, i.e., quartz vein-type, greisen-skarn-type, greisen-type, and granite-type, representing a progression characterized by the increasing content and decreasing range of variation of high field strength elements (HFSEs), and reflecting a general increase in the degree of evolution of the associated granites. Rare earth element (REE) concentrations suggest that precipitation of cassiterite was insensitive to the redox state of the fluid and that precipitation of cassiterite in the southern Hunan Sn deposits did not require a high-fO2 environment. These findings provide new insights into tin mineralization processes and exploration strategies.

Long-range transport and deposition on the Arctic snowpack of nuclear contaminated particulate matter

The primary environmental concern related to nuclear power is the production of radioactive waste hazardous to humans and the environment. The main scientific and technological problems to address this are related to the storage and disposal of the nuclear waste and monitoring the dispersion of radioactive species into the environment. In this work, we determined an anomalously high 14C activity, well above the modern natural background, on surface and seasonal snow sampled in early May 2019 on glaciers in the Hornsund fjord area (Svalbard). Due to the lack of local sources, the high snow concentrations of 14C suggest long-range atmospheric transport of nuclear waste particles from lower latitudes, where nuclear power plants and treatment stations are located. The analysis of the synoptic and local meteorological data allowed us to associate the long-range transport of this anomalous 14C concentration to an intrusion event of a warm and humid air mass that likely brought pollutants from Central Europe to the Arctic in late April 2019. Elemental and organic carbon, trace element concentration data, and scanning electron microscopy morphological analysis were performed on the same snow samples to better constrain the transport process that might have led to the high 14C radionuclide concentrations in Svalbard. In particular, the highest 14C values found in the snowpack (> 200 percent of Modern Carbon, pMC) were associated with the lowest OC/EC ratios (< 4), an indication of an anthropogenic industrial source, and with the presence of spherical particles rich in iron, zirconium, and titanium which, altogether, suggest an origin related to nuclear waste reprocessing plants. This study highlights the role of long-range transport in exposing Arctic environments to human pollution. Given that the frequency and intensity of these atmospheric warming events are predicted to increase due to ongoing climate change, improving our knowledge of their possible impact to Arctic pollution is becoming urgent.

A database of water chemistry in eastern Siberian rivers

Permafrost degradation leads to considerable changes in river ecosystems. The Eastern Siberian River Chemistry (ESRC) database was constructed to create a spatially extensive river chemistry database to assess climate warming-induced changes in freshwater systems in permafrost-dominated eastern Siberia. The database includes 9487 major ion (Na+, K+, Ca2+, Mg2+, Cl−, SO42− and HCO3−) data of chemical results from 1434 water samples collected mainly in six large river basins in eastern Siberia spanning 1940–2019. Data were obtained from public databases, scientific literature in English and Russian, and researchers and were formatted with a consistent table structure. The database is transparent and reproducible. Climate variable (air temperature and precipitation) data, discharge data, trace element concentration data, and isotope data at the basin and subbasin scales are also provided. This database enhances knowledge about the water chemistry of the permafrost region, especially in eastern Siberia, where data are scarce. The database will be useful to those assessing spatiotemporal changes in river water chemistry associated with permafrost degradation or other environmental stressors in a warmer climate.

Ontogenetic spatial dynamics of the deep-sea teleost Aphanopus carbo in the NE Atlantic according to otolith geochemistry

The spatial distribution of deep-sea fishes is commonly related to major water masses or regional circulatory features that in turn may reflect differences in food-web structure and productivity. Aphanopus carbo is a benthopelagic species that undergoes horizontal and vertical migrations driven by spawning and by feeding, and for which a large-scale clockwise migration around the NE Atlantic is hypothesized. In this work, the adequacy of otolith microchemical composition used as tool to discriminate A. carbo specimens caught at different areas was investigated. Furthermore, potential birth areas and spatial pattern migration throughout the species life cycle were studied. Trace element concentration (TEC) in the otolith edge allowed the discrimination of the locations where specimens were caught and supported the separation between the northern and the southern distribution areas. The existence of two natal sources was suggested based on the separation of otolith core TEC into two groups. Longitudinal multivariate analyses applied to TEC data also sustained the separation of the otoliths into two main groups, but the mixing between them gives support to the species migratory hypothesis. The acceptance of both southern and northern spawning grounds and of migratory movements along the NE Atlantic in both northward and southward directions implies changes to the current migratory hypothesis that might be translated into new definitions of A. carbo stock structure and therefore fisheries management.

Tephrostratigraphy and Magma Evolution Based on Combined Zircon Trace Element and U-Pb Age Data: Fingerprinting Miocene Silicic Pyroclastic Rocks in the Pannonian Basin

We present a novel approach to use zircon as a correlation tool as well as a monitor for magma reservoir processes in silicic volcanic systems. Fingerprinting eruption products based on trace element content and U-Pb dates of zircon offers a promising, previously underestimated tephra correlation perspective, particularly in cases where the main minerals and glass are altered. Using LA-ICP-MS analyses, a rapid and cost-effective method, this study presents U-Pb dates and trace element concentration data of more than 950 zircon crystals from scattered occurrences of early to mid-Miocene silicic ignimbrites in the northern Pannonian Basin, eastern-central Europe. This magmatic phase produced &amp;gt;4000 km3of erupted material, which provide unique stratigraphic marker horizons in central and southern Europe. The newly determined zircon U-Pb eruption ages for the distal pyroclastic deposits are between 17.5 and 14.3 Ma, comparable with the previously published ages of the main eruptive events. Multivariate discriminant analysis of selected trace element concentrations in zircon proved to be useful to distinguish the main volcanic units and to correlate the previously ambiguously categorized pyroclastic deposits with them. Using the zircon trace element content together with published glass data from crystal-poor ignimbrites, we determined the zircon/melt partition coefficients. The obtained values of the distinct eruption units are very similar and comparable to published data for silicic volcanic systems. This suggests that zircon/melt partition coefficients in calc-alkaline dacitic to rhyolitic systems are not significantly influenced by the melt composition at &amp;gt;70 wt% SiO2at near solidus temperature. The partition coefficients and zircon trace element data were used to calculate the equilibrium melt composition, which characterizes the eruption products even where glass is thoroughly altered or missing. Hence, our results provide important proxies for tephrostratigraphy in addition to yielding insights into the complex processes of silicic magma reservoirs.

Trace element analysis reveals bioaccumulation in the squid Gonatus fabricii from polar regions of the Atlantic Ocean

The boreoatlantic gonate squid (Gonatus fabricii) represents important prey for top predators—such as marine mammals, seabirds and fish—and is also an efficient predator of crustaceans and fish. Gonatus fabricii is the most abundant cephalopod in the northern Atlantic and Arctic Ocean but the trace element accumulation of this ecologically important species is unknown. In this study, trace element concentrations (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn) were analysed from the mantle muscle and the digestive gland tissue of juveniles, adult females, and adult males that were captured south of Disko Island off West-Greenland. To assess the feeding habitat and trophic position of this species, stable isotopes of carbon (δ13C) and nitrogen (δ15N) were measured in their muscle tissue. Mercury concentrations were positively correlated with size (mantle length) and trophic position. The Hg/Se ratio was assessed because Se has been suggested to play a protective role against Hg toxicity and showed a molar surplus of Se relative to Hg. Cadmium concentrations in the digestive gland were negatively correlated with size and trophic position (δ15N), which suggested a dietary shift from Cd-rich crustaceans towards Cd-poor fish during ontogeny. This study provides trace element concentration data for G. fabricii from Greenlandic waters, which represents baseline data for a northern cephalopod species. Within West-Greenland waters, G. fabricii appears to be an important vector for the transfer of Cd in the Arctic pelagic food web.

Chemometric evaluation of concentrations of trace elements in intervertebral disc tissue in patient with degenerative disc disease.

The work is designed to uncover the pattern of mutual relation among trace elements and epidemiological data in the degenerated intervertebral disk tissue in humans. Hitherto the reason of the degenerative process is not fully understood. Trace elements are the basic components of the biological compound related both its metabolism as well as environmental exposure. The relation pattern among elements occurs gives new perspective in solving the cause of the disease. We have analysed trace elements content in the 30 intervertebral disc from 22 patients with degenerative disc disease. The concentrations of Al, Cu, Cd, Mo, Ni and Pb were determined with Atomic Absorption Spectrometry. To analyse the multidimentional relation between trace element concentration and epidemiological data the chemometric analysis was applied. The similarity have been shown in occurrence of following pairs: Cd-Mo as well as Mg-Zn. The second pair was correlated with Pb concentration. Pb levels are observed to be competitive to Cu concentration. Cd concentration was related to Zn and Mg deficiency. No single but rather cluster of epidemiological data show observable influence on the TE tissue variance. Zn and Cu was related to the male sex. Operation with orthopedic implants were related to combined Al, Mo and Zn concentration. This is the first chemometric analysis of trace elements in disk tissue. It shows multidimentional relations that are missed by the classical statistic. The analysis shows significant relation. The nature of the relations is the basis for further metabolic and environmental research.

The geographic distribution of trace elements in the environment: the REGARDS study.

Research on trace elements and the effects of their ingestion on human health is often seen in scientific literature. However, little research has been done on the distribution of trace elements in the environment and their impact on health. This paper examines what characteristics among participants in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study are associated with levels of environmental exposure to arsenic, magnesium, mercury, and selenium. Demographic information from REGARDS participants was combined with trace element concentration data from the US Geochemical Survey (USGS). Each trace element was characterized as either low (magnesium and selenium) or high (arsenic and mercury) exposure. Associations between demographic characteristics and trace element concentrations were analyzed with unadjusted and adjusted logistic regression models. Individuals who reside in the Stroke Belt have lower odds of high exposure (4th quartile) to arsenic (OR 0.33, CI 0.31, 0.35) and increased exposure to mercury (OR 0.65, CI 0.62, 0.70) than those living outside of these areas, while the odds of low exposure to trace element concentrations were increased for magnesium (OR 5.48, CI 5.05, 5.95) and selenium (OR 2.37, CI 2.22, 2.54). We found an association between levels of trace elements in the environment and geographic region of residence, among other factors. Future studies are needed to further examine this association and determine whether or not these differences may be related to geographic variation in disease.

Comprehensive Pb‐Sr‐Nd‐Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials

AbstractControlling the accuracy and precision of geochemical analyses requires the use of characterized reference materials with matrices similar to those of the unknown samples being analyzed. We report a comprehensive Pb‐Sr‐Nd‐Hf isotopic and trace element concentration data set, combined with quantitative phase analysis by XRD Rietveld refinement, for a wide range of mafic to ultramafic rock reference materials analyzed at the Pacific Centre for Isotopic and Geochemical Research, University of British Columbia. The samples include a pyroxenite (NIM‐P), five basalts (BHVO‐2, BIR‐1a, JB‐3, BE‐N, GSR‐3), a diabase (W‐2), a dolerite (DNC‐1), a norite (NIM‐N), and an anorthosite (AN‐G); results from a leucogabbro (Stillwater) are also reported. Individual isotopic ratios determined by MC‐ICP‐MS and TIMS, and multielement analyses by HR‐ICP‐MS are reported with 4–12 complete analytical duplicates for each sample. The basaltic reference materials have coherent Sr and Nd isotopic ratios with external precision below 50 ppm (2SD) and below 100 ppm for Hf isotopes (except BIR‐1a). For Pb isotopic reproducibility, several of the basalts (JB‐3, BHVO‐2) require acid leaching prior to dissolution. The plutonic reference materials also have coherent Sr and Nd isotopic ratios (&lt;50 ppm), however, obtaining good reproducibility for Pb and Hf isotopic ratios is more challenging for NIM‐P, NIM‐N, and AN‐G due to a variety of factors, including postcrystallization Pb mobility and the presence of accessory zircon. Collectively, these results form a comprehensive new database that can be used by the geochemical community for evaluating the radiogenic isotope and trace element compositions of volcanic and plutonic mafic‐ultramafic rocks.

Trace element characterization of USGS reference materials by HR-ICP-MS and Q-ICP-MS

A trace-element characterization of United States Geological Survey (USGS) reference materials has been carried out using three different inductively coupled plasma mass spectrometer instruments: Nu Instruments AttoM, Thermo Scientific Element 2, and Agilent 7700x. The six USGS reference materials (BHVO-2, BCR-2, AGV-2, STM-2, RGM-2, and G-3) include both extrusive and intrusive rocks with compositions ranging from mafic to felsic that encompass a wide range of trace element concentrations and mineral phases. The prevalence of these 2nd (and 3rd) generation reference materials among geochemical laboratories and the added care that was taken during sample preparation make this generation of reference materials more suitable for characterization and use by the geochemical community.The mafic-intermediate reference materials (BHVO-2, BCR-2, and AGV-2) had the most abundant published characterization prior to this study, which allowed for thorough and direct comparison with previous studies (and USGS certificates). Published data for these reference materials are relatively well constrained for most elements (i.e., not highly variable) and the results of this study generally correspond well with the literature. This can, at least partially, be attributed to the relatively simple matrices of these reference materials together with their overall smaller range of trace element concentrations.Unlike the mafic-intermediate reference materials, STM-2 lacked any published trace element concentrations prior to this study and data for RGM-2 and G-3 were relatively sparse. Data for STM-2 and RGM-2 from this study are compared to preliminary USGS certificates, while data for G-3 are compared to the G-2 certificate values; for comparison with published data, RGM-1 and G-2 are included. Overall, the published data for RGM and G are variable across the entire suite of trace elements and display poorer agreement with the data from this study. This can be explained by the fact that, in addition to the comparison between generations that may add heterogeneity, the felsic reference materials have relatively complex matrices and larger ranges in trace element concentration. Given the new data that this study provides, the felsic reference materials can now be used by the geochemical community to produce more accurate trace element concentration analyses of felsic materials.By using three instruments with different configurations, this study also serves as a comparison of the performance of each instrument in response to an array of geologic matrices. The data reveal that the tested instruments are all capable of producing accurate and precise trace element concentration data over a range of geologic matrices, provided that each instrument is carefully operated within its dynamic range. In many cases, this could be accomplished simply by ensuring proper dilution of samples; however, when matrices are more complex, the use of medium and high resolutions can be useful in reducing the amount of preparative chemistry that is required to manage highly variable trace element concentrations within a single sample as well as any potential isobaric interferences.

Chalcophile behavior of thallium during MORB melting and implications for the sulfur content of the mantle

AbstractWe present new laser ablation ICP‐MS trace element concentration data for 28 elements in 97 mid‐ocean ridge basalt (MORB) glasses that cover all major spreading centers as well as Tl concentration data for all mineral phases in five lherzolites from the Lherz massif, France. The ratio between the elements thallium (Tl) and cerium (Ce) is nearly constant in MORB, providing evidence that the depleted MORB mantle (DMM) has uniform Ce/Tl. Lherzolite mineral data reveal that sulfides are heterogeneous and contain between 23 and 430 ng/g of Tl while all other minerals contain Tl below the analytical detection limit of ∼1 ng/g. We argue that Tl in MORB is controlled by residual sulfide during mantle melting. To investigate the observed relationship between Tl and Ce, we conduct models of fractional mantle melting, which show that the constant Ce/Tl in MORB is only reproduced if the ratio between clinopyroxene and sulfide in the upper mantle varies by less than 10%. In addition, the rate of melting for these two phases must be nearly identical as otherwise melt depletion and refertilization processes would lead to Ce/Tl fractionation. These model results allow us to establish a relationship for the sulfur content of DMM: [S]DMM = SCSS × Mcpx /Rcpx, where SCSS is the sulfur concentration of a silicate melt at sulfide saturation, Rcpx is the melt reaction coefficient, and Mcpx is the modal abundance of clinopyroxene in the DMM. Using this equation, we calculate that the average upper mantle sulfur concentration is 195 ± 45 μg/g.

Sr and Nd isotopic compositions of apatite reference materials used in U–Th–Pb geochronology

Apatite is an important common U- and Th-bearing accessory mineral in igneous, metamorphic and clastic sedimentary rocks. The advent of in situ U–Th–Pb apatite geochronology by the SIMS and LA-(MC)-ICP-MS methods has demonstrated the importance of having uniform and homogeneous reference materials. Recently, it has been shown that Sr and Nd isotopic data combined with U–Pb age and trace element concentration data can provide important constraints on apatite paragenesis because this phase usually exhibits high Sr and REE concentrations but has low Rb/Sr ratios which result in negligible corrections for the ingrowth of radiogenic Sr. However, as apatite can potentially have complex internal structures resulting from multiple thermal events, such as inherited cores and metamorphic overgrowths, requires that the Sr and Nd isotopic data should be measured with high spatial resolution. However isobaric interferences hamper the precise determination of Sr or Nd isotopic compositions in LA-MC-ICP-MS analysis. In this work we undertook in situ measurements of Sr and Nd isotopic compositions of eleven apatite reference materials (AP1, AP2, Durango, MAD, Otter Lake, NW-1, Slyudyanka, UWA-1, Mud Tank, McClure Mountain and SDG) commonly used in U–Th–Pb geochronology. Our obtained Sr and Sm–Nd isotopic compositions for these apatite samples are consistent with those values obtained by solution-based methods (isotope dilution and ion chromatography) using MC-ICP-MS or TIMS, which demonstrates the reliability and robustness of our analytical protocol.

Utility of multiple chemical techniques in archaeological residential mobility studies: Case studies from Tiwanaku‐ and Chiribaya‐affiliated sites in the Andes

In the south central Andes, archaeologists have long debated the extent of Tiwanaku colonization during the Middle Horizon (AD 500-1000). We tested the hypotheses regarding the nature of Tiwanaku influence using strontium isotope, trace element concentration, and oxygen isotope data from archaeological human tooth enamel and bone from Tiwanaku- and Chiribaya-affiliated sites in the south central Andes. Strontium isotope analysis of 25 individuals buried at the Tiwanaku-affiliated Moquegua Valley site of Chen Chen demonstrates that it was likely a Tiwanaku colony. In contrast, no immigrants from the Lake Titicaca Basin were present in 27 individuals analyzed from the San Pedro de Atacama cemeteries of Coyo Oriental, Coyo-3, and Solcor-3; it is likely that these sites represent economic and religious alliances, but not colonies. However, strontium isotope analysis alone cannot distinguish movement between the Tiwanaku- and Chiribaya-affiliated sites in the Moquegua and Ilo Valleys of southern Peru. Analyzing oxygen isotope and trace element concentration data and comparing it with strontium isotope data from the same individuals provides a more detailed picture of residential mobility in the Tiwanaku and Chiribaya polities. In addition to monitoring diagenetic contamination, trace element concentration data identified movement during adulthood for certain individuals. However, these data could not distinguish movement between the Moquegua and Ilo Valleys. While oxygen isotope data could clearly distinguish the high-altitude sites from others, more data is needed to characterize the local oxygen isotope ratios of these regions. These data demonstrate the potential for archaeological reconstruction of residential mobility through multiple lines of evidence.

Multi-Element Isotope Dilution Sector Field ICP-MS: A Precise Technique for the Analysis of Geological Materials and its Application to Geological Reference Materials

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Trace element distribution in US groundwaters: a probabilistic assessment using public domain data

A large database of dissolved-fraction groundwater concentrations for Ag, As, Ba, Be, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, Se, Tl, Sn, V and Zn was constructed using public domain data. Data analysis techniques for multiply-censored sample populations were used to extract salient information regarding sample populations from the raw data. The results of this work show that trace element concentrations are approximately log-normally distributed. Median values for <90% censored sample populations range from 0.2 to 35 μg l −1. Minimum to maximum concentrations range as high as 7 orders of magnitude for certain elements (e.g. Zn). This work provides a rapid, cost-effective screening tool for evaluating groundwater quality based on observed trace element concentration data.

Mantle reservoir geochemistry from statistical analysis of ICP-MS trace element data of equatorial mid-Atlantic MORB glasses

We report Inductively Coupled Plasma Mass Spectrometer (ICP-MS) trace element concentration data for 21 elements in 51 basaltic glasses recovered from 58 stations along a 1500-km segment of the equatorial mid-Atlantic Ridge (MAR; 5°N to 5°S). Isotope systematics of these glasses revealed mixing between two isotopically distinct (Schilling, J.-G., Hanan, B.B., McCully, B., Kingsley, R.H., 1994. Influence of the Sierra Leone mantle plume on the equatorial MAR: a Nd–Sr–Pb isotopic study. J. Geophys. Res., 99, 12005–12028.) HIMU and DM mantle sources. Trace element data presented here describe three distinct mantle reservoirs. Based on our new trace element data, we identified three, and possibly four, end-member mantle reservoirs beneath the equatorial MAR. HIMU-type signatures dominate the glasses from the northern equatorial MAR (5°N to 0°) with La/Ba, La/Th and rare earth element (REE) values similar to P-type mid-Ocean Ridge Basalts (MORB; 0.1, 9.11, (La/Yb) N =5.5, respectively). The basaltic glasses from the southern region (0° to 5°S) are mildly radiogenic in Pb and light REE depleted with N-type MORB trace element values for La/Ba, La/Th and REE (0.8, 40.0, (La/Yb) N <0.6, respectively). We estimate the mantle magma-source characteristics and identify the relative contributions of the mantle end-member components in the glasses erupted along the 1500-km transect using the trace element concentration data. Specifically, we recognize the presence of a statistically and geochemically distinct mantle reservoir depleted in Th and Ba relative to average depleted MORB between the Romanche and the Chain fracture zones. To reach the full potential of this data set, we model mantle reservoir compositions using a modification of Q-MODE factor analysis. Multivariate classification and reduction of these data clearly distinguish trace element groups each reflective of mantle source heterogeneities present in this region of the MAR. Statistical analysis of these new trace element and available Nd–Sr–Pb isotope data for the same samples defines four statistically significant distinct end-member mantle components. The binary mixing model developed previously from geochemical data that invoked the mixing of two mantle reservoirs, HIMU and N-MORB, cannot adequately explain the variance in these trace element data. Incompatible element concentrations and ratios best describe the modeled end-members reservoirs, which are HIMU (HPM), transitional N-MORB (TNM), depleted N-MORB (DNM) and an fourth incompatible element-enriched component (EPM). The statistically determined end-members explain 100% of the geochemical variance in the population but their modeled compositions may be related to process controlled variation. We clarify the relationship between statistical and geochemical reservoirs and conclude that a multiple mantle component model involving three of the identified reservoirs is clearly necessary to describe, specifically, the trace element characteristics of the equatorial mid-Atlantic MORBs. Our statistical methods yield tabulated trace element concentration data for each of these the modeled mantle components and provide insights into the MAR system, unavailable by any other technique, by allowing an estimation of the relative contributions of these end-member components in each of the 51 basaltic glass samples.

Infilling history of a Neoproterozoic intracratonic basin: Nd isotope provenance studies of the Uinta Mountain Group, Western United States

Neodymium isotope and selected trace element concentration data were obtained from 27 samples of shales and arkosic sandstones comprising the Neoproterozoic Uinta Mountain Group (UMG) in north-eastern Utah and northwestern Colorado to determine the provenance of siliciclastic detritus deposited in this region and to reconstruct aspects of the Proterozoic geologic history of the southern margin of the Archean Wyoming Province. In the east lobe of the Uinta Mountains, coarse-grained components of the Jesse Ewing Canyon Formation, the oldest recognized formation of the UMG, have measured ϵ Nd values of −23 to −28 and were most probably derived from Archean basement of the Wyoming Province to the north. Fine-grained sediment in the southern portions of the Jesse Ewing Canyon Formation and shales and quartz arenites from overlying undifferentiated UMG all contain at least a component of detritus derived from Proterozoic crust. In the west lobe, the oldest members of the UMG (the Red Castle Lake, Gilbert Peak and Moosehorn Lake Formations) and arkosic arenite comprising the northern portions of the overlying Mount Watson Formation were also derived exclusively from Archean sources. However, as in the east lobe, the more mature sandstones that dominate the southern sections of the Mount Watson Formation have isotopic compositions that require a significant Proterozoic-crust derived detrital component. Our data support a model in which sedimentary rocks with an Archean provenance represent the preserved remnants of alluvial fans marking the northern margin of the basin in which the UMG was deposited. A source for these sediments within the Archean Wyoming Province is consistent with the high light rare-earth element (LREE) and Th abundances of finegrained, low ϵ Nd, sedimentary rocks, given that Late Archean granitic rocks within the Wyoming province have similar trace element characteristics. Sediments with Proterozoic components in both the east and west lobes were apparently deposited from a fluvial system that transported sediment along the basin axis. The Proterozoic detrital component in these sediments originated either through direct erosion of the Colorado Province in the Neoproterozoic, or through erosion of ‘mixed’ Archean and Proterozoic crust located to the east of the UMG basin that originally formed during the Paleoproterozoic accretion of the Colorado Province to the southern margin of the Wyoming craton.

Trace Element Distributions in the Gulf Stream Adjacent to the Southeastern Atlantic Continental Shelf—Influence of Atmospheric and Shelf Water Inputs

As part of an effort to define processes that control the exchange of trace elements between southeastern Atlantic shelf waters and the Gulf Stream at the shelf boundary we determined the vertical distribution of particulate Al, Fe, Mn, Ni, Cu, Zn, Pb, and Cd and total dissolvable Fe, Ni, Cu, Zn, Pb, and Cd in the Gulf Stream adjacent to the shelf. Simultaneous determination of the particulate forms of Cu, Ni, and Cd and potential carrier phase indicators such as particulate Al, Fe, Mn, and organic C permitted assessment of the relative importance of clay minerals, hydrous oxides, and organic matter in the control of the trace element content of suspended matter. Particulate trace element concentration data were used in conjunction with a first-order removal model to estimate downward vertical fluxes of Fe, Mn, Ni, Cu, Pb, and Cd. Comparison of these flux estimates with atmospheric inputs of these same elements indicated that, with the possible exceptions of Mn and Cu, vertical processes largely control the distribution of trace elements in the Gulf Stream and that these processes are primarily biological in nature. Estimates of "new" production, in concert with an estimated vertical flux of C and the observed nitrate concentration profile, were used to predict a vertical eddy diffusion coefficient of ~0.4 cm2∙s−1 in the highly stratified region of the Gulf Stream. Injection of trace elements from shelf waters into surface Gulf Stream waters, with the possible exceptions of Mn and Cu, are apparently masked by a combination of atmospheric input and large-scale physical mixing processes.

Role of trace element partition coefficients in models of andesite genesis

Orogenic andesite magmas probably evolve at 1100 to 900°C, have between 1 and 5 wt. % H 2O and f O 2 above the NiNiO buffer during phenocryst precipitation and may be saturated with a second fluid phase prior to eruption. Consequently, many solid/liquid trace element partition coefficients appropriate to andesites are higher than for basalts, perhaps due to the presence of fewer octahedrally coordinated sites in andesite liquids as well as to lower temperatures. Simple quantitative interpretation of trace element concentration data for orogenic andesites in general or for most specific suites is not possible using available partition coefficients. Fractional crystallization models involving magnetite or amphibole or both seem less at odds with available data than do models invoking equilibration with subducted oceanic crust or overlying peridotite. Critical choices between simple models, or identification of supplementary or more complex processes, require a more rigorous data base than presently available.