Enrichment Of Trace Elements Research Articles

Mantle transition zone-derived EM1 component beneath NE China: Geochemical evidence from Cenozoic potassic basalts

The isotopic characteristics of the sub-oceanic mantle are well established, but in continental regions these properties are usually obscured, and therefore controversial, because of the potential effects of crustal contamination together with lithospheric mantle metasomatism and melting. The so-called EM1 (Enriched Mantle-1) signature, characterized by low 206Pb/204Pb and 143Nd/144Nd ratios, is particularly problematic in this respect because EM1-type OIB sources are commonly attributed to recycled crust and/or lithospheric mantle. In this paper we show that a suite of Cenozoic potassic basalts from NE China displays many previously unrecognized correlations between chemical and isotopic parameters, which tightly constrain the isotopic characteristics of an extreme EM1-type mantle source located in the asthenosphere. Its radiogenic isotopes are similar to, but even more extreme than, those of the oceanic endmember composition represented by the Pitcairn hotspot, namely 206Pb/204Pb ≤ 16.5, 143Nd/144Nd ≤ 0.5123 (or εNd≤−6.4), 176Hf/177Hf ≤ 0.2825 (or εHf≤−10.1). These characteristics require a source of recycled crustal material of Precambrian age (∼2.2 Ga). An important new constraint is the Mg isotopic composition of δ26Mg (≤−0.6‰), which is lower than normal mantle (δ26Mg=−0.25±0.07‰) and lower crustal values (δ26Mg=−0.29±0.15‰), but consistent with sedimentary carbonate (δ26Mg=−5.57‰ to −0.38‰). The endmember EM1 source produced high-SiO2 melts with low MgO, CaO/Al2O3 and δ26Mg values, exceptionally high K/U ≅ 50,000, Ba/Th ≅ 400, low U/Pb ≅ 0.06, and positive Zr and Hf anomalies. The chemical and isotopic parameters of this potassic basalt suite form binary mixing arrays, one end point of which is the inferred asthenospheric EM1 reservoir, whereas the other is a more ordinary, depleted mantle component, which is also sampled by local lithospheric mantle xenoliths. These binary arrays include well-developed correlations between Sr, Nd, Hf, Pb and Mg isotopes, negative correlations of 206Pb/204Pb with K2O, K/U, Hf/Hf⁎, positive correlations of δ26Mg with MgO, and 143Nd/144Nd with Fe2O3T and U/Pb.We propose that the EM1 reservoir contains recycled ancient carbonate-bearing sediments, subducted into the mantle transition zone, where K, Rb, Ba and Pb are sequestered by K-hollandite as suggested by Murphy et al. (2002) for the Gaussberg lamproites. Loss of small amounts of carbonate melt extracted Th, U and some of the LREE, while retaining K, Rb, Ba, Pb, Zr and Hf in the residue, thereby generating the observed trace element anomalies. In Cenozoic time, this deep EM1 reservoir ascended into the shallow asthenosphere and underwent low-degree partial melting, at pressures below the stability field of K-hollandite, thereby releasing K, Rb and Ba into the melt. The partial melts ascended through subcontinental lithosphere and were progressively modified by interaction with the lithospheric mantle, thus accounting for the linear chemical and isotopic trends noted above. This interaction imposed a progressively more depleted character on the erupted melt, both in terms of isotopic composition and trace element enrichment.

Tracking the onset of Phanerozoic-style redox-sensitive trace metal enrichments: New results from basal Ediacaran post-glacial strata in NW Canada

A global rise in oxygen levels has been proposed to coincide with the Ediacaran to Cambrian radiation of animals, yet the precise timing and nature of this change remains unresolved. One hypothesis is that the ocean/atmosphere system became temporarily well-oxygenated in the earliest Ediacaran, directly following the Marinoan Snowball Earth glaciation (~635Ma). The evidence for oxygenation is based on large enrichments of redox-sensitive trace elements in black shale from South China presumably deposited under a euxinic water column. These enrichments meet or exceed the bulk concentrations of redox-sensitive trace elements found in Phanerozoic shale deposited under euxinic water columns. Here we test the early Ediacaran post-Snowball oxygenation hypothesis with new data from a high-resolution, multi-proxy geochemical and sedimentological study of three stratigraphic sections in the earliest Ediacaran Sheepbed Formation of the Mackenzie and Wernecke Mountains, NW Canada. Iron speciation data from all sections suggest that the local water column was dominantly ferruginous, with a notable exception of probable euxinic conditions recorded in part of one section. Redox-sensitive elements show no appreciable enrichments in the basal Sheepbed Formation, with maximum concentrations of molybdenum, vanadium, uranium and chromium only slightly above world average shale values. The lack of substantial elemental enrichments within the Sheepbed Formation is consistent with results from coeval ferruginous strata in Svalbard. The dominance of local ferruginous conditions in NW Canada cannot alone account for the muted redox-sensitive element enrichments as V, U, and Cr are thought to be enriched under these conditions, and samples deposited under euxinic conditions also lack Phanerozoic-style enrichments. These contrasting results from different localities highlight a need to further investigate the veracity of trace metal enrichments in all localities as representing global redox conditions as the results have important implications for the timing of oxygenation with respect to early animal evolution.

Covellite of the Semenov-2 hydrothermal field (13°31.13′ N, Mid-Atlantic Ridge): Enrichment in trace elements according to LA ICP MS analysis

As a result of LA ICP MS analysis of sulfides of the Semenov-2 hydrothermal field, it is established that covellite, which replaces Zn sulfides, is enriched in most trace elements. The Ga, Ni, and In contents in it do not vary, whereas Mn, Co, and Cd are lower than in sphalerite. The distribution of trace elements in covellite, which replaces Cu–Fe sulfides, is distinct: it is enriched in Cd, Sb, Pb, and Bi, whereas the contents of other elements are either lower or invariant. Covellite, which replaces Zn sulfides, is enriched in all trace elements relative to that replacing Cu–Fe sulfides. Enrichment of covellite in trace elements relative to primary sulfides was favored by oxidation of the hydrothermal fluid by seawater, which is similar to the processes of submarine oxidation of ancient massive sulfide deposits. Covellite is also a host to invisible gold and silver in ores of the Semenov-2 field along with toxic elements such as As, Se, Te, Tl, and Cd.

Geochemistry and mineral chemistry of pyroxenite xenoliths and host volcanic alkaline rocks from north west of Marand (NW Iran)

The Plio-Quaternary alkaline volcanic rocks from the northwest of Marand (NW Iran) consist of trachy-andesites, trachy-basaltic andesites, leucite-tephrites and tephrites. They display a distinct LILE and LREE enrichment, a HFSE depletion (Ta, Ti, and Nb) and high Ba/Ta and Ba/Nb ratios, which are among the characteristics of subduction-derived magmatic rocks. The investigated clinopyroxenite xenoliths mostly occur within the trachy-andesites and more rarely within the trachy-basaltic andesite rocks. These xenoliths, which have a cumulate texture, are classified into four groups based on their mineralogical and chemical features. Group 1 contains clinopyroxene and amphibole as the main minerals. This group does not indicate a clear enrichment in incompatible trace elements in contrast with the Groups 2 and 4, where Ba, Th and U are enriched. Major element contents of clinopyroxenes and amphiboles of Group 1 xenoliths are similar to those of their counterparts of intermediate volcanic rocks. In addition, their contents of compatible elements such as Cr and Ni (whole rock) are also the same, implying a similar magmatic origin. Group 2 contains clinopyroxene and phlogopite as the main minerals. This group, similarly to potassic and ultrapotassic volcanic rocks, is enriched in LREE compared to HREE and unlike the intermediate volcanic rocks, does not contain amphibole. Their 143Nd/144Nd and 86Sr/87Sr ratios are also different. Given the Cr and Ni contents, the REE pattern shape and the chemical composition of clinopyroxene and phlogopite, it seems that the parental melt of this group is similar to the one of potassic and ultrapotassic volcanic rocks. Group 3 contains clinopyroxene and biotite as the main minerals. The REE pattern of this group, unlike those of Groups 1, 2 and 4, has a relatively flat slope. In addition, the content of compatible elements, such as Cr and Ni, also differ as well as the chemical composition of clinopyroxene and mica, which are also different from those of volcanic rocks. Group 4 clinopyroxenites contain clinopyroxene, phlogopite and amphibole as the main minerals. The LREE-enriched patterns and the Ba, U and Pb enrichment of this group are similar to those of the Group 2. The samples of this group on the other hand differ from those of the Group 2 clinopyroxenites in terms of crystal size, crystallization depth, Cr and Ni contents, and chemical composition of clinopyroxene. The parental melt of this group is similar to that of the intermediate volcanic rocks.

Constraining late stage melt-peridotite interaction in the lithospheric mantle of southern Ethiopia: evidence from lithium elemental and isotopic compositions

Lithium (Li) elemental and isotopic compositions for mineral separates of coexisting olivine, orthopyroxene and clinopyroxene of mantle xenoliths from the Quaternary volcanic rocks of southern Ethiopian rift (Dillo and Megado) reveal the influence of late stage melt-peridotite interaction on the early depleted and variably metasomatized lithospheric mantle. Two types of lherzolites are reported (LREE-depleted La/Sm(N) = 0.11–0.37 × Cl and LREE-enriched, La/Sm(N) = 1.88–15.72 × Cl). The depleted lherzolites have variable range in Li concentration (olivine: 2.1–5.4 ppm; opx: 1.1–2.3 ppm; cpx: 1.0–1.8 ppm) and in Li isotopic composition (δ7Li in olivine: −9.4 to 1.5‰; in opx: −4.5 to 3.6‰; in cpx: −17.0 to 4.8‰), indicating strong disequilibrium in Li partitioning and Li isotope fractionation between samples. The enriched lherzolites have limited range in both Li abundances (olivine: 2.7–3.0 ppm; opx: 1.1–3.1 ppm; cpx: 1.1–2.3 ppm) and Li isotopic compositions (δ7Li in olivine: −1.3 to +1.3‰; in opx: −2.0 to +5.0‰; in cpx: −7.5 to +4.8‰), suggest that the earlier metasomatic event which lead to LREE enrichment could also homogenize the Li contents and its isotopes. The enriched harzburgite and clinopyroxenite minerals show limited variation in Li abundances and variable Li isotopic compositions. The Li enrichments of olivine and clinopyroxene correlate neither with the incompatible trace element enrichment nor with the Sr-Nd isotopic compositions of clinopyroxene. These observations indicate that the metasomatic events which are responsible for the LREE enrichment and for the Li addition are distinct, whereby the LREE-enrichment pre-dates the influx of Li. The presence of large Li isotopic disequilibria within and between minerals of depleted and enriched peridotites suggest that the lithospheric mantle beneath the southern Ethiopian rift has experienced recent melt-peridotite interaction. Thus, the Li data set reported in this study offer new additional evidence for the existence of late stage metasomatism, which probably occurred at shallow depth briefly before and/or during entrainment and ascent of mantle xenoliths to the surface.

Macroglossia

A study was carried out on the distribution and enrichment of trace elements in the core marine sediments of East Malaysia from three stations at South China Sea and one station each at Sulu Sea and Sulawesi Sea. Five stations of sediment cores were recovered and the vertical concentration profiles of six elements namely Br, Cs, Hf, Rb, Ta, and V were determined using the instrumental neutron activation analysis. The enrichment factor, geoaccumulation index and the modified degree of contamination were used to calculate the anthropogenic and pollution status of the elements in the samples. Except for Cs and Hf, which by the enrichment factor are categorized from minimum enrichment to moderate enrichment in all stations and for V and Rb in Sulu Sea and Sulawesi Sea, which are categorized minimum enrichment, other elements are found to be no enrichment at all stations. The geoaccumulation index of Hf in one station shows moderately polluted and for other elements are unpolluted. However, the modified degree values of all samples are less than 1, suggesting very low contamination of elements found in all the stations.

Geochemical record of methane seepage in authigenic carbonates and surrounding host sediments: A case study from the South China Sea

Sediments at marine methane seep sites provide potential archives of past fluid flow that serve to explore seepage activities over time. Three gravity cores (D-8, D-F, and D-7) were collected from seep sites on the northern slope of the South China Sea where gas hydrates were drilled in the subsurface. Various carbon and sulfur contents, δ13C values of total inorganic carbon (δ13CTIC), δ34S values of chromium reducible sulfur (δ34SCRS), trace element contents, grain size, and AMS 14C dating of planktonic Foraminifera in the sediments were determined to explore the availability of related proxies at seeps and to trace past methane seepage activities. Evidence for the presence of methane seepage and consequently anaerobic oxidation of methane comes from the occurrence of 13C-depleted authigenic carbonate nodules (δ13C values as low as −49‰) discovered at an interval of 150–200cm in core D-7. This finding is supported by high S/C ratios and molybdenum enrichment in the same interval. However, low contents of CRS and negative δ34SCRS values are present. It is suggested to reflect a transient methane seepage event, which continued for about 1ka based on the 14C ages. Cores D-8 and D-F have δ13CTIC values close to zero, low S/C ratios and CRS contents, negative δ34SCRS values, and no trace element enrichment, suggesting a negligible impact of methane-seepage on the sediments. The negative δ34SCRS values of the studied seep-impacted and background sediments suggest that the application of δ34SCRS alone as a proxy to identify AOM-related process may be insufficient. Sediment carbon-sulfur-trace element systematics and 14C ages used here have the potential to be a promising tool to recognize transient methane seepages and constrain their timescales.

Biomineralisation of the ferromanganese crusts in the Western Pacific Ocean

Ferromanganese (Fe-Mn) crusts are deep-sea sedimentary polymetallic minerals that are explored for their economic potential, particularly for Mn, Cu, Co, Ni and rare earth elements (REEs). The precipitation mechanism of the metallic elements in crusts has remained controversial between chemical oxidation (abiotic origin) and microbial enzymatic processes (biomineralization). In this study, the microbial mineralization in ferromanganese crusts from the Western Pacific Ocean was explored. Scanning electron microscope (SEM) and transmission electron microscope (TEM) analyses showed abundant micron-scale spherical aggregates of Mn-oxide filaments (20–80nm), which are closely associated with filamentous cells within the biofilm (biofilm mineralization) exist within the stromatolitic structure. The high-throughput sequencing of 16S rRNA and phylogenetic analysis suggests that biofilms are dominated by three Mn-oxidizing bacterial species from the families Bacillus, Arthrobacter and Pseudomonas. In addition, Mn concentration in the biofilms is approximately 108 times that of the associated seawater (2.3ppbMn). Iron (16.2wt%), Cu (0.11wt%), Co (0.719wt%) and Ni (0.459wt%) were found in the biofilms via X-ray Fluorescence Spectrometer (XRF) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). We suggest that biomineralization provides a new perspective for understanding Fe-Mn crustal-related mineral deposits, and the ultra-high microbial trace element enrichment ability is noteworthy. Utilization of microbial activities in accumulating precious metals from seawater may offer a viable alternative for the world’s metal production in the future.

Distribution of Trace Elements in Core Marine Sediments of Coastal East Malaysia by Instrumental Neutron Activation Analysis

A study was carried out on the distribution and enrichment of trace elements in the core marine sediments of East Malaysia from three stations at South China Sea and one station each at Sulu Sea and Sulawesi Sea. Five stations of sediment cores were recovered and the vertical concentration profiles of six elements namely Br, Cs, Hf, Rb, Ta, and V were determined using the instrumental neutron activation analysis. The enrichment factor, geoaccumulation index and the modified degree of contamination were used to calculate the anthropogenic and pollution status of the elements in the samples. Except for Cs and Hf, which by the enrichment factor are categorized from minimum enrichment to moderate enrichment in all stations and for V and Rb in Sulu Sea and Sulawesi Sea, which are categorized minimum enrichment, other elements are found to be no enrichment at all stations. The geoaccumulation index of Hf in one station shows moderately polluted and for other elements are unpolluted. However, the modified degree values of all samples are less than 1, suggesting very low contamination of elements found in all the stations.

Potential of Hydrothermal Altered Rocks as Potential Scenario for Search of Biosignatures in Exoplanets

Hydrothermally altered ignimbrite tuff has been characterized by x-ray fluorescence (XRF) and x-ray diffraction (micro-XRD). XRF elemental distribution maps show a clear localization of elements according to their weathering and solubility in water, with particular enrichment in iron, sulfur and trace elements within the boundary. Three distinctive patters were observed by XRD; Parent rock (ignimbrite) and boundary's shows enrichment of iron-bearing minerals (sulfides and arsenates and ferro-glaucophane) and recrystallized zone (quartz, sanidine and clays). This segmented arrangement of elements, may stablish a redox potential within the rock and the environment, and in the other hand the inherent porosity of zeolites, allows water and gas transport from the environment to the boundary, resemble a fuel cell array.

Composition and conditions of crystallization of zircon from the rare-metal ores of the Gremyakha–Vyrmes Massif, Kola Peninsula

The first data on the composition and inner structure of zircon, one of the main ore minerals of the rare-metal metasomatites of the Gremyakha–Vyrmes alkaline-ultramafic massif, are reported. Early zircon generations are enriched in Y and REE and contain numerous inclusions of rock-forming and accessory minerals of metasomatites, as well as syngenetic fluid inclusions of calcite, thorite and thorianite. Late generations differ in the elevated Hf content and contain no inclusions. The elevated concentrations of Ca and Th in the central zones of crystals are related to the presence of numerous micron-sized inclusions of calcite and thorium phases. All zircon varieties have extremely low U and Pb contents. Concentrations and distribution patterns of incompatible and rare-earth elements in zircon from the metasomatites of the Gremyakha–Vyrmes Massif are similar to those of syenite pegmatites and magmatic carbonatites around the world. Mineral from these associations shows a positive Ce anomaly and elevated HREE contents. According to the compositions of zircon and thorite inclusion in it and experimental data on the simultaneous synthesis of these minerals, the crystallization temperature of zircon was 700–750°С. Using Ti-in-zircon temperature dependence, late zurcon was formed at temperature of 700–750°С. The rare-metal metasomatites are formed at the final stages of the massif formation, presumably after foidolites. Carbonatites could initiate metasomatic reworking of foidolites and accumulation of trace metals in them. The evolution of the primary alkaline–ultramafic melt toward the enrichment in trace elements was mainly controlled by crystallization differentiation.

Chemical layering in the upper mantle of Mars: Evidence from olivine‐hosted melt inclusions in Tissint

AbstractMelting of Martian mantle, formation, and evolution of primary magma from the depleted mantle were previously modeled from experimental petrology and geochemical studies of Martian meteorites. Based on in situ major and trace element study of a range of olivine‐hosted melt inclusions in various stages of crystallization of Tissint, a depleted olivine–phyric shergottite, we further constrain different stages of depletion and enrichment in the depleted mantle source of the shergottite suite. Two types of melt inclusions were petrographically recognized. Type I melt inclusions occur in the megacrystic olivine core (Fo76‐70), while type II melt inclusions are hosted by the outer mantle of the olivine (Fo66‐55). REE‐plot indicates type I melt inclusions, which are unique because they represent the most depleted trace element data from the parent magmas of all the depleted shergottites, are an order of magnitude depleted compared to the type II melt inclusions. The absolute REE content of type II displays parallel trend but somewhat lower value than the Tissint whole‐rock. Model calculations indicate two‐stage mantle melting events followed by enrichment through mixing with a hypothetical residual melt from solidifying magma ocean. This resulted in ~10 times enrichment of incompatible trace elements from parent magma stage to the remaining melt after 45% crystallization, simulating the whole‐rock of Tissint. We rule out any assimilation due to crustal recycling into the upper mantle, as proposed by a recent study. Rather, we propose the presence of Al, Ca, Na, P, and REE‐rich layer at the shallower upper mantle above the depleted mantle source region during the geologic evolution of Mars.

Rare earths and trace elements contents in leaves: A new indicator of the composition of atmospheric dust

The relationship between the trace element distribution in atmospheric particles and leaves of some exposed plants in the environment was recently demonstrated. This indication would suggest that the trace element analysis of leaves in these plants could provide information about the composition, nature and origin of the atmospheric dust dispersed in the environment. In order to corroborate this hypothesis, the distribution of trace elements and Rare Earths were studied in leaves of some endemic plants, in the atmospheric fallout and in soils of rural, urban and industrial ecosystems in Sicily. These elements have been chosen to discriminate the source and nature of different source on atmospheric dust and the larger capability of the composition of the latter materials to influence the metal ion distribution in leaves of studied plants rather than the soil composition. These evidences are related to the recognition both of positive La anomaly and trace element enrichments in studied leaves and to their particular V/Th and Co/Ni signature. On the other hand, some particular normalised REE features recognised in leaves suggest that a limited contribution to the REE budget in studied leaves is provided by the REE migration from roots.

Trace element distribution and enrichment patterns of Ediacaran-early Cambrian, Ziyang selenosis area, Central China: Constraints for the origin of Selenium

Ziyang County is one of the two major regions in Central China exposed to Selenium (Se) poisoning. To understand the origin of anomalous Se enrichment strata of the Ediacaran-early Cambrian period (ca. 635–520Ma) in the area of Ziyang affected by selenosis, major and trace elements were analyzed for 468 samples collected from the Lujiaping Formation in Ziyang County, Central China.Se is the most highly enriched trace element in the Lujiaping Formation of the Ediacaran-early Cambrian period. Se concentrations vary from 0.03 to 303ppm, with an average of 16ppm, or >324 times the concentration found in the upper continental crust. The average Se content of Bed 6 (approximately 63m thick) is the highest, at 49.20ppm (1.45–154ppm). The Lujiaping Formation is highly enriched in Cd (×53), S (×31), Mo (×22) and As (×13), compared to the upper continental crust. It is slightly enriched in V (×8.07), Ba (×7.65), Ga (×7.24), Zn (×7.22), U (×5.43), Cu (×4.02), Bi (×2.55), Tl (×2.16), Ni (×1.75), P (×1.03), and depleted in Pb (0.97), Cr (0.96), Sr (0.81), Li (0.79), In (0.69), Sc (0.69), Be (0.38), Cs (0.36), Co (0.30), Rb (0.29), and Th (0.27).All Eu/Eu* for the forty anomalous Se-enrichment samples (Se=42–303ppm) of the 1st Member (1.09–2.09, average=avg.=1.40), 2nd Member (1.20–1.38, avg.=1.29), 3rd Member (1.12–4.00, avg.=2.38) and 4th Member (2.51–4.48, avg.=3.56), show positive Eu anomalies and an increasing trend upward. However, Eu/Eu* of two samples are 0.90 (HSBY324, Bed 4 of 1st Member) and 0.95 (HSBY401, Bed 6 of 1st Member), which indicate that they are characterized by hydrothermal sediments, except HSBY324 and HSBY401 of 1st Member. Based on these elements' geochemical and petrographic characteristics, we conclude that these samples are of hydrothermal origin. There is also a strong positive correlation between Se and Ba (RSe-Ba=0.738**, n=40). In three point X-ray energy spectrometric analysis of black shale mineral anomalous Se-enrichment samples (HSBY601), the nor.C measurements of Ba (L Series) are 55.50wt.%, 54.94wt.% and 27.20wt.%, respectively, with the corresponding Atom. C of 14.80, 14.50 and 5.72at.%. Thus, the main Se source was derived from hydrothermal fluids, of anomalous Se-enrichment strata of Ediacaran-early Cambrian (ca. 635–520Ma) of South Qinling Mountain.

A Statistical Description of Concurrent Mixing and Crystallization during MORB Differentiation: Implications for Trace Element Enrichment

The pattern of trace element enrichment and variability found in differentiated suites of basalts is a simple observable, which nonetheless records a wealth of information on processes occurring from the mantle to crustal magma chambers. The incompatible element contents of some mid-ocean ridge basalt (MORB) sample suites show progressive enrichment beyond the predictions of simple models of fractional crystallization of a single primary melt. Explanations for this over-enrichment have focused on the differentiation processes in crustal magma chambers. Here we consider an additional mechanism and focus instead on the deviation from simple fractionation trends that is possible by mixing of diverse mantle-derived melts supplied to magma chambers. A primary observation motivating this strategy is that there is significant chemical diversity in primitive high-MgO basalts, which single liquid parent models cannot match. Models were developed to simulate the compositional effects of concurrent mixing and crystallization (CMC): diverse parental melts were allowed to mix, with a likelihood that is proportional to the extent of fractional crystallization. Using a simple statistical model to explore the effects of concurrent mixing and crystallization on apparent liquid lines of descent, we show how significant departure from Rayleigh fractionation is possible as a function of the diversity of trace elements in the incoming melts, their primary MgO content, and the relative proportion of enriched to depleted melts. The model was used to make predictions of gradients of trace element enrichment in log[trace element]–MgO space. These predictions were compared with observations from a compilation of global MORB and provide a test of the applicability of CMC to natural systems. We find that by considering the trace element variability of primitive MORB, their MgO contents and degree of enrichment, CMC accurately predicts the pattern of trace element over-enrichment seen in global MORB. Importantly, this model shows that the relationship between over-enrichment and incompatibility can result from mantle processes: the fact that during mantle melting maximum variability is generated in those elements with the smallest bulk Kd. Magma chamber processes are therefore filtering the signal of mantle-derived chemical diversity to produce trace element over-enrichment during differentiation. Finally, we interrogate the global MORB dataset for evidence that trace element over-enrichment varies as a function of melt supply. There is no correlation between over-enrichment and melt supply in the global dataset. Trace element over-enrichment occurs at slow-spreading ridges where extensive steady-state axial magma chambers, the most likely environment for repeated episodes of replenishment, tapping and crystallization, are very rarely detected. This supports a model whereby trace element over-enrichment is an inevitable consequence of chemically heterogeneous melts delivered from the mantle, a process that may operate across all rates of melt supply.

Geochemical characteristics and mode of occurrence of trace elements in coal at West Bokaro coalfield

The mineralogy and trace element contents in coals from the West Bokaro coalfield, which is the one of the biggest Gondwana coalfields of India, were studied to delineate enrichment of trace elements and their modes of occurrence. Elemental concentrations with reference to their crustal abundances indicated that coals are relatively enriched in As (4.4–15.5 mg/kg), Cd (0.3–3.0 mg/kg), Cu (28.0–68.1 mg/kg) and V (46.6–178.0 mg/kg); depleted in Co (10.8–28.4 mg/kg), Mn (7.6–483.4 mg/kg), Ni (13.0–31.6 mg/kg), Cr (14.2–85.5 mg/kg) and Zn (5.25–70.4 mg/kg). The concentration of As, Cd, Co, Cu and V were higher than the average values of world and Indian coals. Mineralogical study carried out by X-ray diffraction shows that quartz and kaolinite occur as dominant mineral phases in this coal. Fourier transform infrared spectroscopy pattern suggests organic structures primarily containing aromatic nuclei, aliphatic side chain and some oxygen containing groups. The modes of occurrence of trace elements present in these coals have been determined through statistical approach. Both Cu and Cr are more closely associated with mineral matter, whereas Co is dominantly present with its organic form. The concentrations of Cd, Mn, Ni, Zn, As and V have apparently occur in both organic and inorganic constituents. This study would be helpful to assess the potential environmental impacts during mining and combustion of this coal.

Trace and Rare Earth Element Geochemistry of Black Shales in Triassic Kasimlar Formation, Anamas-Akseki Platform, Western Taurids, Turkey

The Triassic black shale sequence of Kasimlar Formation in the Anamas - Akseki Platform, Western Taurids, Turkey do not show any trace element enrichment. But trace element values of Black shales from the Kasimlar Formation are broadly comparable with those of the average upper continental crust. While there are slightly enrichments in As, Bi, Zn, Nb, Cu, Pb, Cs and Sb. The other elements are slightly depleted in black shales according to those of upper continental crust (UC). Organic carbon content of the black shales is between 05 and 0.71% but reach 3.78% (averaging as 0.52%). The black shales do not show metal/TOC correlation. Compared to the black shales of Kasimlar Formation and upper continental crust; The black shales show a significant increase in HREE and LREE. Our data show slightly negative Ce anomalies (Ce/Ce* as low as 0.94) and positive Eu anomalies (Eu/Eu* as high as 3.33). Ce/Ce* and Eu/Eu* values recorded in the depositional environment indicate low oxygenated and anaerobic (reducing) conditions.

Characterization of depositional conditions for lacustrine oil shales in the Eocene Jijuntun Formation, Fushun Basin, NE China

The strike-slip Fushun Basin hosts a lacustrine oil shale interval of ca. 50–300m in the Eocene (Lutetian) Jijuntun Formation. The oil shale deposits consist of the lower lean oil shale unit (LOSU) and the upper rich oil shale unit (ROSU). In outcrop areas, the identified depositional cycles of ca. 8–10m and 5–8m in thickness record the stacking of massive and non-laminated oil shales in the LOSU and fine- and coarse-laminated oil shales in the ROSU, respectively.Depositional conditions in the paleo-Jijuntun Lakes were synoptically reconstructed based on sedimentary features, trace element and organic geochemical proxies. Oxic to suboxic, fresh-water conditions were prevailing in the paleo-Jijuntun Lakes during deposition of the LOSU, and then evolved into oxygen-deficient, fresh- to mildly brackish-water conditions during deposition of the ROSU, as revealed by the concentrations of redox- and salinity-sensitive trace elements (e.g. V/Ni, V/Cr, Ni/Co and Sr/Ba ratios, and boron content) in the oil shales. Warm to cool and humid to arid climate (represented by e.g. Sr/Cu and Rb/Sr ratios) could result in the deepening of water column (from ca. 20–30m to ca. 100m) and saline stratification superposed on pre-existing thermal stratification in the paleo-Jijuntun Lakes. A systematical decrease (approximately one order of magnitude) in the concentrations of most trace elements (except for boron and Co) in the coaly oil shale in the lowermost LOSU, relative to those in the other oil shales in the Jijuntun Formation indicates the significant change of organic matter (OM) input from higher plant (especially coaly materials) to aquatic plankton. This is partly consistent with the variations of OM input from terrestrial higher plant and aquatic organisms (type II kerogen in the LOSU) to lacustrine algae (type I kerogen in the ROSU) as revealed by biomarkers. The slight to significant enrichment or depletion of few trace elements (i.e. Mn and Mo) in these immature to low-mature oil shale deposits may be associated with low to moderate productivities of aquatic plankton and/or incompletely oxygen-free conditions in the paleo-Jijuntun Lakes.

Groundwater flow and residence time in a karst aquifer using ion and isotope characterization

In order to identify the origin of the main processes that affect the composition of groundwater in a karstic aquifer, a hydrogeochemical and isotopic study was carried out of water from numerous observation wells located in Sierra de Gador, a semiarid region in SE Spain. Several natural and anthropogenic tracers were used to calculate groundwater residence time within this complex aquifer system. Analysis of major ions enabled the principal geochemical processes occurring in the aquifer to be established, and the samples were classified into four distinctive solute groups according to this criterion. Dissolution of carbonate rocks determines the chemical composition of less mineralized water. In another group, the concurrent dissolution of dolomite and precipitation of calcite in gypsum-bearing carbonate aquifer, where the dissolution of relatively soluble gypsum controls the reaction, are the dominant processes. Marine intrusion results in highly mineralized waters and leads to base exchange reactions. The groundwater enrichment of minor and trace elements allowed classification of the samples into two classes that are linked to different flow patterns. One of these classes is influenced by a slow and/or deep regional flow, where the temperature is generally elevated. The influence of sulphate reduces by up to 40 % the barium concentration due to the barite precipitation. Isotope data (T, 14C) confirm the existence of recent local flows, and regional flow system, and ages of ground water may reach 8000 years. The importance of gypsum dissolution in this aquifer is proved by the δ34S content.

Trace element composition of silicate inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite: Evidence for diamond growth from slab melts

The trace element compositions of inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite, Brazil, are presented. Literature data for mineral/melt partition coefficients were collated, refitted and employed to interpret inclusion compositions. As part of this process an updated empirical model for predicting the partitioning behaviour of trivalent cations for garnet–melt equilibrium calibrated using data from 73 garnet-melt pairs is presented. High levels of trace element enrichment in inclusions interpreted as former calcium silicate perovskite and majoritic garnet preclude their origin as fragments of an ambient deep mantle assemblage. Inclusions believed to represent former bridgmanite minerals also display a modest degree of enrichment relative to mantle phases. The trace element compositions of ‘NAL’ and ‘CF phase’ minerals are also reported. Negative Eu, Ce, and Y/Ho anomalies alongside depletions of Sr, Hf and Zr in many inclusions are suggestive of formation from a low-degree carbonatitic melt of subducted oceanic crust. Observed enrichments in garnet and ‘calcium perovskite’ inclusions limit depths of melting to less than ~600km, prior to calcium perovskite saturation in subducting assemblages. Less enriched inclusions in sub-lithospheric diamonds from other global localities may represent deeper diamond formation. Modelled source rock compositions that are capable of producing melts in equilibrium with Juina-5 ‘calcium perovskite’ and majorite inclusions are consistent with subducted MORB. Global majorite inclusion compositions suggest a common process is responsible for the formation of many superdeep diamonds, irrespective of geographic locality. Global transition zone inclusion compositions are reproduced by fractional crystallisation from a single parent melt, suggesting that they record the crystallisation sequence and melt evolution during this interaction of slab melts with ambient mantle. All observations are consistent with the previous hypothesis that many superdeep diamonds are created as slab-derived carbonatites interact with peridotitic mantle in the transition zone.