Low Concentrations Of Trace Elements Research Articles

Norican Steel - An Assessment of the Archaeological Finds at the Magdalensberg Site, Carinthia, Compared to the “Celtic Trove” of Gründberg Hill, Linz

The analysis of Celtic steel products from depots found in the area north of the Danube has shown that their excellent properties are due to the choice of unalloyed or alloyed steel bars that were shaped by fire-forging. Phosphorus was used as an alloying element, while carbon was added through carburizing of the workpiece. Was this forging technique also known to regions in the very heart of the Alps? Our analysis set out to find an answer to this question. The Celtic smiths in the inner Alpine regions used shaft furnaces to produce steel loops with numerous slag inclusions but very low contents of trace elements in the steel matrix. In a series of process steps in the smithy - trimming the steel loop, forging into bars, sheafing, carburizing, hardening - the steel properties demanded by the customers were achieved. Phosphorus was not deliberately employed as an alloying metal in the valleys of the Central Alps. The fact that the forging technique was tailored to the actual product appears to underlie the high quality of Norican steel.

The use of quartz concentrate (acid-insoluble residue) as a sample medium in lithogeochemistry and regolith exploration studies: development of a method

Quartz concentrates provide a general sample medium with low background concentration of minor and trace elements. They can be obtained from most rock types by hot nitric acid or aqua regia leach, sometimes supplemented by sulphuric acid leach. The concentrates consist of a mixture of primary quartz, secondary quartz resulting from wallrock alteration and insoluble minerals such as sericite and alkali feldspar. Multi-element analysis enables detection of even the weakest mineralization and wallrock alteration, as expressed mainly by Ba, Ca, Ge, K, Li, Mn, Na, Rb and Sr, in addition to Au, Pb, and Zn. Both wallrock alteration patterns and secondary dispersion trails remain preserved in the quartz concentrates, even in deeply weathered terrain. Results of 14 case histories of various types of gold and base metal deposits are compared.

EXTREME STRUCTURAL AND COMPOSITIONAL VARIABILITY IN THE LANZO SOUTH PERIDOTITE DOCUMENTS A COMPOSITE HISTORY OF MELT-ROCK INTERACTION

EXTREME STRUCTURAL AND COMPOSITIONAL VARIABILITY IN THE LANZO SOUTH PERIDOTITE DOCUMENTS A COMPOSITE HISTORY OF MELT-ROCK INTERACTION

Exsolution of thortveitite, yttrialite, and xenotime during low-temperature recrystallization of zircon from New Caledonia, and their significance for trace element incorporation in zircon

Recrystallized zircon grains in a phengite-epidote-chlorite schist from north-eastern New Caledonia contain as inclusions a mineral assemblage consisting of celadonite, kaolinite, quartz, Fe-oxy-hydroxide, smectite, chlorite, xenotime-(Y), thortveitite, yttrialite, and allanite-(Ce). This assemblage formed during low-temperature (<100 °C) seafloor alteration of a plagioclase-rich mafic rock and represents the first documented evidence of this alteration event in the high-P belt of northeastern New Caledonia. The survival of this low-temperature mineral paragenesis in zircon of a rock that has undergone subsequent eclogite-facies metamorphism testifies to the strength and value of zircon as a container for mineral inclusions. Thortveitite (Sc 2 Si 2 O 7 ) and yttrialite (Y 2 Si 2 O 7 ) inclusions in the altered zircon cores represent a new occurrence for these minerals and suggest that they may be more common than is currently recognized. The altered zircon cores generally have lower trace-element contents than the pristine igneous zircon cores and we suggest that thortveitite, yttrialite, and xenotime-(Y) formed as a result of trace-element expulsion from zircon during low-temperature recrystallization. Trace-element concentrations in the zircon cores indicate that trivalent cations (REE, Y, Sc) in zircon cannot be charge-balanced by xenotime substitution alone. Pentavalent cation concentrations (Nb, As) are also insufficient for charge balance. The presence of thortveitite (Sc 2 Si 2 O 7 ) and yttrialite (Y 2 Si 2 O 7 ) suggests that trivalent cations in zircon might be charge-balanced either by monovalent anions substituting for oxygen or by small monovalent cations such as H occurring interstitially in the zircon lattice.

Censoring approach to the detection limits in X-ray fluorescence analysis

We demonstrate that the effect of detection limits in the X-ray fluorescence analysis (XRF), which limits the determination of very low concentrations of trace elements and results in appearance of the so-called “nondetects”, can be accounted for using the statistical concept of censoring. More precisely, the results of such measurements can be viewed as the left random censored data, which can further be analyzed using the Kaplan–Meier method correcting the data for the presence of nondetects. Using this approach, the results of measured, detection limit censored concentrations can be interpreted in a nonparametric manner including the correction for the nondetects, i.e. the measurements in which the concentrations were found to be below the actual detection limits. Moreover, using the Monte Carlo simulation technique we show that by using the Kaplan–Meier approach the corrected mean concentrations for a population of the samples can be estimated within a few percent uncertainties with respect of the simulated, uncensored data. This practically means that the final uncertainties of estimated mean values are limited in fact by the number of studied samples and not by the correction procedure itself. The discussed random-left censoring approach was applied to analyze the XRF detection-limit-censored concentration measurements of trace elements in biomedical samples.

Trace element incorporation into quartz: A combined study by ICP-MS, electron spin resonance, cathodoluminescence, capillary ion analysis, and gas chromatography

Pegmatite quartz from different occurrences in Norway and Namibia was investigated by a combination of ICP-MS, Electron Spin Resonance (ESR), Capillary Ion Analysis (CIA) and Gas Chromatography (GC) to quantify trace elements in very low concentrations and to determine their position in the quartz structure. The studied quartz samples show similar geochemical characteristics with low contents of most trace elements. Remarkable are the elevated concentrations of Al (36–636 ppm), Ti (1.6–25.2 ppm), Ge (1.0–7.1 ppm), Na (5.2 to >50 ppm), K (1.6 to >100 ppm) and Li (2.1–165.6 ppm). These elements are preferentially incorporated into the quartz lattice on substitutional (Al, Ti, Ge) and interstitial (Li, Na, K) positions. Li + was found to be the main charge compensating ion for Al, Ge and Ti, whereas some ppm of Na and K may also be hosted by fluid inclusions. Ti may be incorporated as substitutional ion for Si or bound on mineral microinclusions (rutile). The results of the ESR measurements show that there may be a redistribution of alkali ions during irradiation. The diamagnetic [AlO 4/M +] 0 center transforms into the paramagnetic [AlO 4] 0 center, whilst the compensating ions diffuse away and may be captured by the diamagnetic precursor centers of [GeO 4] 0 and [TiO 4] 0 to form paramagnetic centers ([TiO 4/Li +] 0, [GeO 4/Li +] 0). In general, fluid inclusions in pegmatite quartz can be classified as H 2O-CO 2-NaCl type inclusions with water as the predominant volatile. Among the main elements hosted by fluid inclusions in quartz are Na, K, NH 4, Ca, Mg and the anionic complexes Cl −, NO 3 −, HCO 3 − and SO 4 2−. Gas analysis of trapped fluids shows volatile components in the following order of abundance: H 2O > CO 2 > N 2(+) ≥ CH 4 > COS > C 2 and C 3 hydrocarbons. Additionally, traces of Co, Ni, Zn, Pb, and Cu were detected by CIA in fluid inclusions of some samples. There are indications that the REE and Rb are also bound in fluid inclusions, however, the concentrations of these elements are too low to be measured by CIA. Assuming that the REE preferentially occur in fluid inclusions, the typical chondrite normalized REE distribution patterns with tetrad effects and a distinct negative Eu anomaly would reflect the composition of the mineralizing fluid. For a number of elements, especially those with extremely low concentrations, the “type” of incorporation in quartz could not directly be determined. We conclude that these ions either are too large to substitute for the small Si 4+ ion or they are not soluble in the mineralizing fluids to be hosted by fluid inclusions. Some of these elements, which are concentrated in the specific mineralization of certain pegmatites, are not present in elevated concentrations in the paragenetic pegmatite quartz itself. This was observed, for instance, for Be, Cs and Rb in the Li (Be-Cs-Rb) pegmatites of Rubicon or for Nb and Ta for Nb-Ta bearing pegmatites from Norway. It may be concluded that the concentrations of these trace elements in quartz do not reflect the mineralization and that these elements thus, cannot be used as petrogenetic indicator.

Microbial acidification and pH effects on trace element release from sewage sludge

Leaching of sludge-borne trace elements has been observed in experimental and field studies. The role of microbial processes in the mobilization of trace elements from wastewater sludge is poorly defined. Our objectives were to determine trace element mobilization from sludge subjected to treatments representing microbial acidification, direct chemical acidification and no acidification, and to determine the readsorption potential of mobilized elements using calcareous sand. Triplicate columns (10-cm diameter) for incubation and leaching of sludge had a top layer of digested dewatered sludge (either untreated, acidified with H 2SO 4, or limed with CaCO 3; all mixed with glass beads to prevent ponding) and a lower glass bead support bed. Glass beads in the sludge layer, support layer or both were replaced by calcareous sand in four treatments used for testing the readsorption potential of mobilized elements. Eight sequential 8-day incubation and leaching cycles were operated, each consisting of 7.6 d of incubation at 28 °C followed by 8 h of leaching with synthetic acid rain applied at 0.25 cm/h. Leachates were analyzed for trace elements, nitrate and pH, and sludge layer microbial respiration was measured. The largest trace element, nitrate and S losses occurred in treatments with the greatest pH depression and greatest microbial respiration rates. Cumulative leaching losses from both microbial acidification and direct acidification treatments were >90% of Zn and 64–80% of Cu and Ni. Preventing acidification with sludge layer lime or sand restricted leaching for all trace elements except Mo. Results suggested that the primary microbial role in the rapid leaching of trace elements was acidification, with results from direct acidification being nearly identical to microbial acidification. Microbial activity in the presence of materials that prevented acidification mobilized far lower concentrations of trace elements, with the exception of Mo. Trace elements mobilized by acidification were readsorbed by calcareous sand when present.

Petrology and geochemistry of a diamondiferous lherzolite from the Premier diamond mine, South Africa

This paper reports on the petrology and geochemistry of a diamondiferous peridotite xenolith from the Premier diamond mine in South Africa. The xenolith is altered with pervasive serpentinisation of olivine and orthopyroxene. Garnets are in an advanced state of kelyphitisation but partly fresh. Electron microprobe analyses of the garnets are consistent with a lherzolitic paragenesis (8.5 wt.% Cr 2O 3 and 6.6 wt.% CaO). The garnets show limited variation in trace element composition, with generally low concentrations of most trace elements, e.g. Y (<11 ppm), Zr (<18 ppm) and Sr (<0.5 ppm). Garnet rare earth element concentrations, when normalised against the C1 chondrite of McDonough and Sun (Chem. Geol. 120 (1995) 223), are characterised by a rare earth element pattern similar to garnet from fertile lherzolite. All diamonds recovered are colourless. Most crystals are sharp-edged octahedra, some with minor development of the dodecahedral form. A number of crystals are twinned octahedral macles, while aggregates of two or more octahedra are also common. Mineral inclusions are rare. Where present they are predominantly small black rosettes believed to consist of sulfide. In one instance a polymineralic (presumably lherzolitic) assemblage of reddish garnet, green clinopyroxene and a colourless mineral is recognised. Infrared analysis of the xenolith diamonds show nitrogen contents generally lower than 500 ppm and variable nitrogen aggregation state, from 20% to 80% of the ‘B’ form. When plotted on a nitrogen aggregation diagram a well defined trend of increasing nitrogen aggregation state with increasing nitrogen content is observed. Carbon isotopic compositions range from −3.6 ‰ to −1.3 ‰. These are broadly correlated with diamond nitrogen content as determined by infrared spectroscopy, with the most negative C-isotopic compositions correlating with the lowest nitrogen contents. Xenolith mantle equilibration temperatures, calculated from nitrogen aggregation systematics as well as the Ni in garnet thermometer are on the order of 1100 to 1200 °C. It is concluded that the xenolith is a fertile lherzolite, and that the lherzolitic character may have resulted from the total metasomatic overprinting of pre-existing harzburgite. Metasomatism occurred prior to, or accompanied, diamond growth.

Petrology and geochemistry of a diamondiferous lherzolite from the Premier diamond mine, South Africa

This paper reports on the petrology and geochemistry of a diamondiferous peridotite xenolith from the Premier diamond mine in South Africa. The xenolith is altered with pervasive serpentinisation of olivine and orthopyroxene. Garnets are in an advanced state of kelyphitisation but partly fresh. Electron microprobe analyses of the garnets are consistent with a lherzolitic paragenesis (8.5 wt.% Cr2O3 and 6.6 wt.% CaO). The garnets show limited variation in trace element composition, with generally low concentrations of most trace elements, e.g. Y (<11 ppm), Zr (<18 ppm) and Sr (<0.5 ppm). Garnet rare earth element concentrations, when normalised against the C1 chondrite of McDonough and Sun (Chem. Geol. 120 (1995) 223), are characterised by a rare earth element pattern similar to garnet from fertile lherzolite. All diamonds recovered are colourless. Most crystals are sharp-edged octahedra, some with minor development of the dodecahedral form. A number of crystals are twinned octahedral macles, while aggregates of two or more octahedra are also common. Mineral inclusions are rare. Where present they are predominantly small black rosettes believed to consist of sulfide. In one instance a polymineralic (presumably lherzolitic) assemblage of reddish garnet, green clinopyroxene and a colourless mineral is recognised. Infrared analysis of the xenolith diamonds show nitrogen contents generally lower than 500 ppm and variable nitrogen aggregation state, from 20% to 80% of the ‘B’ form. When plotted on a nitrogen aggregation diagram a well defined trend of increasing nitrogen aggregation state with increasing nitrogen content is observed. Carbon isotopic compositions range from −3.6 ‰ to −1.3 ‰. These are broadly correlated with diamond nitrogen content as determined by infrared spectroscopy, with the most negative C-isotopic compositions correlating with the lowest nitrogen contents. Xenolith mantle equilibration temperatures, calculated from nitrogen aggregation systematics as well as the Ni in garnet thermometer are on the order of 1100 to 1200 °C. It is concluded that the xenolith is a fertile lherzolite, and that the lherzolitic character may have resulted from the total metasomatic overprinting of pre-existing harzburgite. Metasomatism occurred prior to, or accompanied, diamond growth.

Selenium and iodine intakes and status in New Zealand and Australia.

Most New Zealand soils contain relatively low concentrations of the anionic trace elements F, I and Se. Some areas of Australia also have a history of I deficiency. In view of current interest in establishing nutrient reference intakes for Se and I in New Zealand and Australia, it is timely to review current understanding of the intakes and status of these two elements. In spite of a recent increase in Se status, the status of New Zealanders remains low compared with populations of many other countries and may still be considered marginal, although the clinical consequences of the marginal Se status are unclear. There are no recent reports of blood Se levels in Australia, but earlier reports indicate that they were generally greater than those of New Zealanders. Similarly, the consequences of decreasing I status in Australia and New Zealand are unclear. Mild I deficiency in New Zealand has resulted in enlarged thyroid glands indicating an increased risk of goitre. Currently there is little evidence, however, of any associated clinical disease. Public health recommendations to reduce salt intake, together with the reduction in I content of dairy products, are likely to result in further decreases in the I status of New Zealand and Australian residents. Some action is needed to prevent this decline and it may be necessary to consider other means of fortification than iodized salt. The consequences of possible interactions between Se and I in human nutrition are also unclear and no practical recommendations can be made.

Three-dimensional flow and trace metal mobility in shallow Chalk groundwater, Dorset, United Kingdom

The three-dimensional groundwater flow and the hydrogeochemical regime have been determined in the Bere Stream valley, North Dorset Downs, southern England. The dual porosity characteristics of the Portsdown Chalk have been established using geophysical and hydrochemical borehole logging. Chemical properties have been established using major and trace element analyses of depth samples and groundwaters. The study site is located at the unconfined-confined boundary of the Chalk aquifer, where it is overflowing in the observation boreholes. The Chalk dips locally at about 5 m/km to the south–east under Palaeogene confining beds and three distinctive flow horizons may be recognised. The Chalk groundwater is of Ca–HCO 3 type and three separate geochemical groundwater zones were also determined with depth, having different oxygen levels and trace element characteristics. (1) A shallow O 2-rich zone with around 80% dissolved O 2 and low trace element concentrations. (2) A mixing and transition zone with significant concentrations of trace elements and high trace metal concentrations at its base: manganese 29 μg/l, nickel 55 μg/l, cadmium 146 μg/l, and zinc 214 μg/l. (3) A deeper zone with depleted oxygen (5–20% dissolved O 2) and with longer water residence times shown by higher Mg/Ca and K/Na ratios as well as higher Sr and F. The groundwater geochemistry in the Chalk aquifer is dominated by incongruent reactions with the fine-grained carbonate sediments, which release trace element impurities to the water. Some of the metals are co-precipitated with Mn- and Fe-oxide phases on fissure surfaces, whilst producing a purer calcite. During subsequent recrystallisation to purer iron- and manganese-oxides on fissure surfaces under specific geochemical and hydrodynamic conditions, trace metals are released into the fissure water. The results demonstrate the need to monitor quality stratification and the changes in the groundwater baseline chemistry in areas close to the redox boundary which, in the dual porosity Chalk is likely to be a diffuse zone with exchange between oxygen poor matrix waters and more oxic water flowing through the fissures.

RARE EARTH AND TRACE ELEMENTS IN AMPHIBOLES OF OCEANIC GABBROS (MARK AREA, MID-ATLANTIC RIDGE) AT MEDIUM- TO LOW-TEMPERATURE SEAFLOOR ALTERATION

The gabbro pile cored at the ODP sites 921-924 (Mid-Atlantic Ridge) underwent subseafloor alteration under polyphase retrograde recrystallization from very high temperatures in a ductile deformation regime to amphibolite and greenschist facies under transitional to brittle regimes (Gaggero and Cortesogno, 1997). To complement the study on the highest grade conditions (Cortesogno et al., 2000), amphiboles developed in different textural sites during the amphibolite to greenschist facies alteration of an olivine gabbro and an Fe-Ti oxide gabbro were analysed for REE, HFSE, LILE, LLE (Li, Be, B) and volatile elements (H, F, Cl) using SIMS. Brown, amphibolite facies, Mg-hornblendes grading to actinolitic hornblendes (Ti 16795-8645 ppm), which had replaced pyroxenes or filled veins, were analysed. The normalised C1 patterns of the pseudomorphic grains were, on the whole, comparable to those of the higher-temperature titanian amphiboles (Cortesogno et al., 2000), whereas the hornblendes filling the veins showed abundances of normalised Nb, La, Ce, Nd, Sm, Gd, Dy, Y, Er, Yb about 10 times higher with moderately increased Eu. On the contrary, Sr, Zr, Ti, Cr were lower. The REE and trace elements were largely controlled by heritage from clinopyroxene, water–amphibole partitioning and water–rock interactions. Green hornblendes (Ti 3492-207 ppm) that had filled the veins within the amphibolite facies, at lower temperatures, under the brittle regime, had C1 normalised patterns parallel to those of the brown hornblendes filling the fractures; the element contents being controlled by microsite equilibria. On the whole, the late actinolite filling of the fractures had low trace and RE element contents, and a positive Eu anomaly; the trace and REE element level decreased in the pseudomorphic grains. The tremolite pseudomorphic on olivine had a C1 normalised pattern parallel to, but with lower values than, the veinfilling hornblendes, except for very low Nb. The pattern was also comparable to the vein-filling actinolites, except for higher Dy, Y, Er, Yb and a negative Eu anomaly. On the whole the H2O content of the amphiboles decreased and F increased with the metamorphic temperatures, whereas Cl increased in the greenschist facies actinolites.

Petrogenesis of the Ulsan carbonate rocks from the south‐eastern Kyongsang Basin, South Korea

Abstract The petrogenesis of the Ulsan carbonate rocks in the Mesozoic Kyongsang Basin of South Korea, which have previously been interpreted as limestone of Paleozoic age, is reconsidered in the present study. Within the Kyongsang Basin, a small volume of carbonate rocks, containing a magnetite deposit and spatially associated ultramafic rocks, is surrounded by sedimentary, volcanic and granitic rocks of the Mesozoic age. The simple cross‐cutting relationships and other outcrop features of the area indicate that the carbonate rocks are an intrusive phase and younger than the other surrounding Mesozoic rocks. The Ulsan carbonates have low concentrations of rare earth elements (REE) and trace elements with the carbon and oxygen isotope values in the range of δ13CPDB = 2.4 to 4.0‰ and δ18OSMOW = 17.0 to 19.5‰. Outcrop evidence and geochemical signatures indicate that the Ulsan carbonates were formed from crustal carbonate melts, which were generated by the melting/fluxing of crustal carbonate materials, caused by the emplacement‐related processes of alkaline A‐type granitic rocks. Compared to typical mantle‐derived carbonatites associated with silica‐undersaturated, strongly peralkaline systems, the relatively small size and geochemical characteristics of the Ulsan carbonates reflect carbonatite genesis in a silica‐saturated, weakly alkali intrusive system. Major deep‐seated tectonic fractures formed by the collapse of the cauldron or the rift system associated with the opening of the East Sea (Japan Sea) might have facilitated the ascent of the crustal carbonate melts.

Geochemical comparisons between estuaries with non‐industrialised and industrialised catchments: The Huon and Derwent River estuaries, Tasmania

The adjacent Huon and Derwent estuaries in Tasmania have similar climatic and physical characteristics, and provide a good comparison between relatively uncontaminated and industrially polluted estuaries, respectively. Representative samples were collected from both estuaries and analysed for grainsize and trace‐element content (using X‐ray fluorescence and neutron activation analyses). The Huon estuary drains a predominantly forested and agricultural catchment and contains low (baseline) concentrations of trace elements, including lead, zinc and copper. In contrast, the Derwent estuary has a geologically similar yet larger catchment and it passes through an industrialised area in the midestuarine reach. A zinc refinery has, in the past, been a major source of trace‐element contamination. These contaminants are distributed downstream from the refinery by combined fluvial and tidal activity, while the latter also causes upstream movement of contaminants during non‐flood periods. Significant upstream contamination is limited by fluvial bottom flows remobilising contaminated fine sediment during flood periods. Maximum contamination occurs in the region around the refinery with values in the surface sediments ranging from 40 to 565 times baseline levels and from 2 to 55 times the Australian Interim Sediment Quality Guidelines high‐levels for aquatic sediments (maximum 22593 ppm Zn, 3866 ppm Pb and 1182 ppm Cu). In the lower Derwent estuary, contaminant distribution is inversely related to tidal‐flow velocities and is most prominent in the lower energy muddy substrates. Trace‐metal levels in the more recent surficial aquatic sediments are slightly lower than those recorded in a previous study from the area, possibly reflecting the stricter environmental controls now operating.

Trace elements in flour and bran from common and tartary buckwheat

The contents of Se, Cr, Rb, Zn, Fe, Co, Sb, Ba, Ni, Ag, Hg and Sn were analysed in the flour and bran of common and tartary buckwheat, obtained by milling in a stone mill. In both species most trace elements are concentrated mainly in the bran. However, there are relatively small differences in the contents of iron, antimony, and chromium between flour (extraction rate 55%) and bran fractions. In tartary buckwheat fine flour (extraction rate 42%) there is a lower trace element content than in normal flour. The potential use of buckwheat bran as a dietary source of Zn, and Se, is indicated.

Geochemistry of Lavas from the Emperor Seamounts, and the Geochemical Evolution of Hawaiian Magmatism from 85 to 42 Ma

The Hawaiian–Emperor Seamount Chain (ESC), in the northern Pacific Ocean, was produced during the passage of the Pacific Plate over the Hawaiian hotspot. Major and trace element concentrations and Sr–Nd–Pb isotopic compositions of shield and post-shield lavas from nine of the Emperor Seamounts provide a 43 Myr record of the chemistry of the oldest preserved Hawaiian magmatism during the Late Mesozoic and Early Cenozoic (from 85 to 42 Ma). These data demonstrate that there were large variations in the composition of Hawaiian magmatism over this period. Tholeiitic basalts from Meiji Seamount (85 Ma), at the northernmost end of the ESC, have low concentrations of incompatible trace elements, and unradiogenic Sr isotopic compositions, compared with younger lavas from the volcanoes of the Hawaiian Chain (<43 Ma). Lavas from Detroit Seamount (81 Ma) have highly depleted incompatible trace element and Sr–Nd isotopic compositions, which are similar to those of Pacific mid-ocean ridge basalts. Lavas from the younger Emperor Seamounts (62–42 Ma) have trace element compositions similar to those of lavas from the Hawaiian Islands, but initial 87Sr/86Sr ratios extend to lower values. From 81 to 42 Ma there was a systematic increase in 87Sr/86Sr of both tholeiitic and alkalic lavas. The age of the oceanic lithosphere at the time of seamount formation decreases northwards along the Emperor Seamount Chain, and the oldest Emperor Seamounts were built upon young, thin lithosphere close to a former spreading centre. However, the inferred distance of the Hawaiian plume from a former spreading centre, and the isotopic compositions of the oldest Emperor lavas appear to rule out plume–ridge interaction as an explanation for their depleted compositions. We suggest that the observed temporal chemical and isotopic variations may instead be due to variations in the degree of melting of a heterogeneous mantle, resulting from differences in the thickness of the oceanic lithosphere upon which the Emperor Seamounts were constructed. During the Cretaceous, when the Hawaiian plume was situated beneath young, thin lithosphere, the degree of melting within the plume was greater, and incompatible trace element depleted, refractory mantle components contributed more to melting.

Discovery of eclogite facies carbonate rocks from the Lindås Nappe, Caledonides, Western Norway

AbstractEclogite facies carbonate rocks have been discovered associated with the granulite–eclogite transitional rocks within Bergen Arc system, Caledonian Orogen of western Norway. The local occurrences of marbles and calc‐silicates are found subparallel to the mafic eclogite facies shear zones on Holsnøy Island. Marbles contain the assemblage calcite (Ca0.99Sr0.01CO3), calcian strontianite (Ca0.18−0.44Sr0.53−0.84CO3), clinopyroxene (Jd7−32), epidote/allanite (Ps0−33), titanite, garnet (Alm52−56Grs28−33Pyp11−16), barite (Ba0.90−0.99Sr0.01−0.10SO4), celestine (Sr0.67−0.98Ba0.01−0.23Ca0.01−0.11SO4), and one apparently homogeneous grain of intermediate composition (Ba0.49Ca0.01Sr0.50SO4). Adjacent eclogites have clinopyroxene with similar jadeite contents (Jd14−34) and similar garnet (Alm51−60Grs26−36Pyp8−14) compositions. The marbles have high contents of Sr (9500–11000 p.p.m) and Y (115–130 p.p.m). However, low concentrations of some key trace elements (110–160 p.p.m. Ba and &lt;5 p.p.m. Nb) appear to indicate that the marble is not a metamorphosed carbonatite. The 87Sr/86Sr ratios range from 0.7051 to 0.7059. Field and petrological relationships suggest that metasomatic reactions and fluids played a significant role in producing and/or modifying the marbles. The breakdown of scapolite in the granulite into carbonates and sulphates during eclogite facies metamorphism may have contributed to the metasomatic formation of the marbles along shear zones.Fluids involved during subduction are an important catalyst for metamorphism and are recognized to have played a critical role in the localized transformation from granulite to eclogite in the Holsnøy Island area. Thermobarometry indicates 640–690 °C and 18–20 kbar for adjacent eclogites and temperatures of 580–650 °C for the calc‐silicates. The marble assemblages are consistent with fluid that is dominantly comprised of H2O (XCO2 &lt; 0.03) under high‐pressure conditions. Phase equilibria of the marbles constrain the fO2 of the fluids and imply oxidizing conditions of the deep crustal fluids. At present the source of the fluids remains unresolved. The results provide additional insights into the variable and evolving nature of fluids related to subduction and high‐pressure metamorphism.

Partial melting to produce high-silica rhyolites of a young bimodal suite: compositional constraints among rhyolites, basalts, and metamorphic xenoliths from the Harney Basin, Oregon

The Rattlesnake Ash Flow Tuff from eastern Oregon includes lithic fragments (xenoliths) of which metasedimentary or metavolcanic lithologies around the vent area in the Harney Basin are samples of the concealed crust. Metasedimentary xenoliths are volcanic lithic to feldspathic graywackes that could be sampling lithologies similar to arc-related terranes to the north that have accreted during Mesozoic time along the Oregon Pacific margin. The importance of finding metaxenoliths in the Rattlesnake Tuff is that they are the first basement samples of southeastern Oregon possibly representative of larger portions of the concealed crust from which voluminous Rattlesnake Tuff and other rhyolites were initially generated during partial melting with subsequent evolution through fractional crystallization. High Ba/Rb ratios of ~30 and La/Yb of ~6.5 of least-evolved Rattlesnake Tuff high-silica rhyolites in combination with other low concentrations of some incompatible trace elements preclude the derivation of least-evolved Rattlesnake Tuff high-silica rhyolite from local low-silica rhyolites through fractionation, which suggests instead that some chemical characteristics could be nearly unmodified signatures derived from partial melting. Rattlesnake metamorphic xenoliths and primitive basalt lavas (HAOT) have the most compatible chemistries as source rock for partial melting among a large range of other local rock compositions. Compositional evidence, comparison with literature data of experimental melts derived from laboratory experiments, and modeling of required effective partition coefficients indicate that least-evolved Rattlesnake Tuff rhyolite was likely generated during dehydration melting of mafic crust at melt percentage ranging from ~5 to 10% with residues as observed in experiments with abundant pyroxene and plagioclase.

An ethnoarchaeological study of chemical residues in the floors and soils of Q'eqchi' Maya houses at Las Pozas, Guatemala

AbstractThis ethnoarchaeological study at the Q'eqchi' Maya village of Las Pozas, Guatemala, aimed to refine the understanding of the relationship between soil chemical signatures and human activities for archaeological applications. The research involved phosphorus, exchangeable ion (calcium, potassium, magnesium, sodium), and trace element analysis of soils and earth floors extracted by Mehlich II, ammonium acetate, and DTPA chelate solutions, respectively. The results showed high levels of phosphorus, potassium, magnesium, and pH in food preparation areas, as well as high phosphorus concentrations and low pH in food consumption areas. The traffic areas exhibited low phosphorus and trace element contents, whereas refuse disposal areas were enriched. These results provide important information for the understanding of space use in ancient settlements. © 2002 Wiley Periodicals, Inc.

Connected fluid evolution in fractured crystalline basement and overlying sediments, Pannonian Basin, SE Hungary

Uplifted crystalline basement highs have played an important role in the hydrologic history of the Pannonian Basin providing conduits for fluid migration during basin evolution. Petrographic, stable isotope, electron microprobe and fluid-inclusion studies support a five–step basin evolution; (1) formation of crystalline core-complexes, (2) percolation of meteoric water through shear zones, (3) basinwide thermal subsidence, (4) hydrologic inversion, and (5) tectonic inversion. Brittle fractures in the basement are the results of uplift during core complex formation and contain pyrite, kaolin, illite, chlorite, calcite, and quartz. Hydrocarbon stains between calcite and quartz and yellow fluorescent, primary, hydrocarbon inclusions in quartz are indicative of migrations of hydrocarbon-bearing fluids during uplift from mid-crustal depth. Further uplift was associated with meteoric water infiltration along shear-zones as recorded by light δ 13C and δ 18O values, low trace element concentrations, all-liquid primary fluid inclusions and encased pollens and cuticules of terrestrial plants in a second fracture-calcite crystallised after quartz. A simultaneous meteoric influence in the overlying Pannonian (12.7–3 Ma) sediments is indicated by extensive plagioclase dissolution, calcite cement geochemistry and low-salinity, all-liquid fluid inclusions. The thermal subsidence of the basin led to isolation of the hydrologic system from the surface. Diminishing meteoric influence is recorded by increasing fluid inclusion salinities of secondary inclusions in calcite and quartz in the basement fractures and of primary inclusions hosted in late calcite and quartz in the sediments. A sudden decrease of the fluid inclusion salinities from 4.5 to 1 wt.% NaCl eq. at ∼130°C both in burial cements and fracture-filling minerals represents a newly established hydrological system, which redistributed the interstitial fluids, including hydrocarbons. This hydraulic inversion is indicated by abundant fluorescent, secondary fluid inclusions in fracture-filling minerals. Finally, the Pliocene to recent tectonic inversion reopened fractures in the crystalline basement, and induced a rapid crystallisation of laumontite. These results support a long-standing (late Miocene to recent) hydraulic connection between fractured crystalline basement and overlying sediments in the central part of the Pannonian Basin.