Changes In Trace Element Composition Research Articles

Trace element changes in rutile from quartzite through increasing P–T from lower amphibolite to eclogite facies conditions

Abstract Low concentrations of Na, Ca, K, Fe, Mg and Al in quartzite commonly prevent the crystallization of index metamorphic minerals, inhibiting the obtainability of thermobarometric calculations. Quartzite typically contains quartz, zircon and rutile; therefore, single-element thermometers, such as Zr-in-rutile, may be applied. We investigate changes in trace-element composition of rutile from quartzite through increasing metamorphic conditions. Studied samples derive from a quartzite package (Luminárias Nappe, Minas Gerais, Brazil) where previous thermobarometric constraints on metapelites showed an increasing metamorphic grade southwards, from high-pressure lower amphibolite facies (580°C; 0.9 GPa) to eclogite facies (630°C; 1.4 GPa). Rutile from the lower-grade facies samples show a large spread in Zr concentrations, with the highest values corresponding to temperature estimates higher than metamorphic conditions affecting those units, and thus interpreted as inherited detrital signatures. A narrower spread in Zr concentration is observed in rutile grains from the higher-grade facies, and estimated Zr-in-rutile temperatures agree with previous thermobarometric constraints. Therefore, we show that at 630°C, Zr contents in detrital rutile from quartzites re-equilibrate. The comparison between the quartzite- and metapelite-hosting rutile grains from the same area shows that the resetting of the geothermometer in the latter seems to occur at slightly lower temperatures (∼50°C lower). Supplementary material: A full dataset of analized trace elements in rutile is available at https://doi.org/10.6084/m9.figshare.c.6793887

Persistence of melt-bearing Archean lower crust for >200 m.y.—An example from the Lewisian Complex, northwest Scotland

Abstract Geochronological data from zircon in Archean tonalite–trondhjemite–granodiorite (TTG) gneisses are commonly difficult to interpret. A notable example is the TTG gneisses from the Lewisian Gneiss Complex, northwest Scotland, which have metamorphic zircon ages that define a more-or-less continuous spread through the Neoarchean, with no clear relationship to zircon textures. These data are generally interpreted to record discrete high-grade events at ca. 2.7 Ga and ca. 2.5 Ga, with intermediate ages reflecting variable Pb loss. Although ancient diffusion of Pb is commonly invoked to explain such protracted age spreads, trace-element data in zircon may permit identification of otherwise cryptic magmatic and metamorphic episodes. Although zircons from the TTG gneiss analyzed here show a characteristic spread of Neoarchean ages, they exhibit subtle but key step changes in trace-element compositions that are difficult to ascribe to diffusive resetting, but that are consistent with emplacement of regionally extensive bodies of mafic magma. These data suggest suprasolidus metamorphic temperatures persisted for 200 m.y. or more during the Neoarchean. Such long-lived high-grade metamorphism is supported by data from zircon grains from a nearby monzogranite sheet. These preserve distinctive trace-element compositions consistent with derivation from a mafic source, and they define a well-constrained U-Pb zircon age of ca. 2.6 Ga that is intermediate between the two previously proposed discrete metamorphic episodes. The persistence of melt-bearing lower crust for hundreds of millions of years was probably the norm during the Archean.

Microstructural, trace element and geochronological characterization of TiO2 polymorphs and implications for mineral exploration

The geochemistry of rutile (TiO2) has recently found its use in mineral exploration with some studies reporting anomalous concentrations of Fe, W, V, Sn and Sb in rutile associated with mineralized ore systems. However, the use of rutile as a prospecting tool is likely to be complicated by the systematic changes in trace element composition with TiO2 polymorph type (anatase, brookite and rutile).Here we present TiO2 trace element and U–Pb geochronological data from the mineralized and barren portions of the Palaeoproterozoic Moorarie Supersuite and (Capricorn Orogen, Western Australia), with a focus on the Minnie Creek Molybdenum Prospect in the northern part of the Gascoyne Province. The barren samples contain all three TiO2 polymorphs (anatase, brookite and rutile). Textures suggest anatase and brookite may have formed during low-T metamorphism, either through replacement of previous rutile grains or titaniferous minerals. Rutile grains from barren samples yield variable U–Pb ages (ca. 3.0–2.2Ga) as well as variable textures and chemical compositions suggesting detrital origins, thus most likely representing metasedimentary units intruded by the Moorarie Supersuite. Rutile grains from the Minnie Creek prospect yield Palaeoproterozoic (ca. 1.77–1.75Ga) U–Pb cooling ages and Nb+Ta concentrations of up to 17wt% that along with inclusions of manganocolumbite, oscillatory and patchy zonation of Nb and Fe, suggest a magmatic origin.The commonly used pathfinder elements for gold and base-metal mineralisation (Fe, Cr, V, W, Sn and Sb) are shown to be systematically lower in anatase and brookite, thus yielding false negatives if polymorph type is not identified during reconnaissance studies. For this reason, a ternary diagram was constructed based on the systematic changes in chemistry of TiO2 polymorphs to provide a relatively fast and easy chemical discrimination of polymorphs in large volumes of reconnaissance data. Furthermore, it is shown that high Al concentrations are characteristic of brookite and, to a lesser degree, anatase but not rutile. In addition, Sn, Nb, Ta and W concentrations in rutile may be more sensitive to igneous processes and may be used to track processes occurring in strongly fractionated granitic magmas such as pegmatites and associated deposits.

The effect of crystal-plastic deformation on isotope and trace element distribution in zircon: Combined BSE, CL, EBSD, FEG-EMPA and NanoSIMS study

Plastically-deformed zircon grains from granulite-facies (Ivrea-Verbano Zone, Southern Alps, Italy) and amphibolite-facies (Tauern Window, Eastern Alps, Austria) shear zones have been investigated. The main focus was on the effects of crystal-plastic deformation on the distribution of trace elements and their isotopes. Zircon grains reveal crystal-plastic deformation patterns in form of (I) gradual bending of the lattice (high density of free dislocations), (II) highly-deformed margins revealing a combination of low- and high-angle boundaries and gradual bending of the lattice, and (III) a low-angle boundary (LAB) network. Chemical and isotopic maps and profiles show that trace elements in zircon are re-distributed in all plastically-deformed domains. Changes in trace element composition along LABs are sometimes revealed by brighter CL and darker BSE signal. LABs and domains of high free-dislocation density have depletion in U, Y, Yb and enrichment in Ce, La and Nd, while Ti and P are either enriched, depleted or remain unaffected, and Hf demonstrates stability. Y and Yb are decreased in concentration across LABs, and have oscillating concentration in domains of high free-dislocation density. Our observations confirm that crystal-plastically deformed domains in zircon act as effective pathways for trace cations.The Pb isotopic system is disturbed by crystal-plastic deformation microstructures, as indicated by relative 207Pb/206Pb ages showing significant discordance in plastically-deformed zircon domains. In deformed domains, a positive correlation between dislocation density and the degree of isotopic age distortion is observed. Fractured or porous domains and domains with high density of (sub)grain boundaries are enriched in common Pb from the matrix, and thus show significantly older relative 207Pb/206Pb ages than pristine domains. In contrast, Pb loss occurs in domains with high free-dislocation density at a distance of 5–10μm from the grain boundary, caused by out-diffusion of radiogenic Pb.This study adds to a growing database on the consequences of crystal-plastic deformation for trace elements and isotopic systems in zircon. We provide additional evidence that such deformation cannot be neglected and may have important implications for zircon geochronology and geochemistry.

Environmental variability between the penultimate deglaciation and the mid Eemian: Insights from Tana che Urla (central Italy) speleothem trace element record

Abstract A trace element record (Mg, Sr, Ba, Al, Si, P, Y, Zn) covering the ca. 133 ka to ca. 124 ka time interval was acquired from a flowstone core from Tana che Urla Cave (central Italy). It was compared with stable isotope data to investigate the environmental evolution in response to regional and extra-regional climate changes in the period corresponding to the latter part of the Penultimate Deglaciation and the first part of the Last Interglacial (Eemian). Trace element geochemical changes on centennial and millennial time scales responded to changes in hydrological input, variations in the supply and transport of catchment erosion products to the cave, including those linked to intense rainfall events, and to the state of the overlying soil and vegetation. Abrupt increases in precipitation and the progressive development of soil and vegetation occurred at ca. 132 ka, in response to the development of the global deglacial phase. The major changes in trace element composition are coherent with the previous hydrological interpretation of speleothem oxygen stable isotope composition (δ18O) as predominantly a rainfall-amount proxy. However, reduced growth rate persisted until ca. 130 ka, suggesting still depressed temperatures. An abrupt event of climatic deterioration, with marked decrease in precipitation and soil degradation, is apparent between ca. 131 and 130 ka. Cool-wet conditions between ca. 132 and 131 ka and the subsequent dry period may represent the local hydrological response to an interval of North Atlantic cooling and ice-rafted-debris (IRD) deposition known as Heinrich event 11 (H11). After 129.6 ka there was a rapid recovery according to all of the studied speleothem properties, indicating the onset of full interglacial conditions. A minor amplitude event of reduced precipitation is recorded within the LIG at ca. 127 ka. The record highlights the growing regional evidence for a complex penultimate deglacial climate involving major reorganization of oceanic and atmospheric patterns.

Monitoring heavy-metal pollution of the coastal waters of Amursky Bay (Sea of Japan) using the brown alga Sargassum miyabei Yendo, 1907

The contents of iron, zinc, nickel, copper, cadmium, and lead in the thalli of the brown alga Sargassum miyabei Yendo, 1907 from the Amursky Bay were determined. The ranges of teh concentrations were as follows: Fe, 166–709; Zn, 4.7–55.7; Ni, 6.48–15.94; Cu, 2.5–22.4; Cd, 3.13–6.25; and Pb, 0.22–19.20 µg/g of dry mass. Based on the data on heavy-metal contents in S. miyabei, the changes in trace-element composition of macrophytes from the mid-1990s until 2011 have been analyzed. It was found that the content of Pb in Sargassum thalli decreased significantly (p = 0.001) almost everywhere; at some stations the Zn concentration decreased by 1.2–2.5 times and that of Cu decreased by 1.1–2.8 times (as a trend). At the same time, high concentrations of Ni and Cd were revealed in S. miyabei from the area of the CHP-1 station, which runs on liquid fuel. In Sargassum that was sampled in the recreational area at the exit of the bay and the entrance cape of the inner bay of the Port Vladivostok, the contents of Zn and Cu increased by 2 times (as a trend), which is obviously caused by an increase of recreational pressure (domestic sewage).

Changes in trace element composition of the brain under conditions of experimental myocardial dysfunction

Aim. Violation of the exchange of trace elements (TE) is an important link in the pathogenesis of cerebral pathology that occurs in people with heart diseases. In order to analyze the changes of the composition of TE, in 19 mature rats quantitative characteristics of TE in brain were identified by emission spectrography under conditions of doxorubicin-induced myocardial dysfunction (MD).Methods and results. We found that the concentration of magnesium and potassium increased, however, the concentration of iron, calcium and sodium conversely significantly decreased. Ratios changes of such TE as Fe/Mg, Ca/K, Ca/Mg were observed.Conclusion. The results indicate ischemic-hypoxic effects in rat brain and can be used as markers of pathological processes.

Trace element mobility during spheroidal weathering of basalts and andesites in Hawaii and Guatemala

Trace element mobility has been studied in spheroidally weathered corestone–shell complexes developed on Late Tertiary and Quaternary volcanic rocks. The parent materials are basalts and andesites related to (1) a subduction zone (Tecuamburro and Moyuta Volcanoes, Guatemala) and (2) a hot spot (Hawaiian Islands of Oahu, Maui and Hawai'i). The initial major element compositions are largely preserved in the corestones; each corestone sample shows major element abundances characteristic of the different magmatic processes through which the lavas were generated. However, the changes in trace element compositions due to weathering show similar patterns in the corestone–shell complexes independent of the tectonic setting and age. Element mobility within the different corestone–shell complex was determined using an isovolumetric reference frame. In this method, bulk density is chosen as an independent measure of the extent of weathering. Based on volumetric concentrations, the notion of element immobility cannot be applied to all the corestone–shell complexes. Elements commonly assumed to be immobile (e.g., Zr, Ti, and Al) vary in volumetric concentration for some corestone–shell complex. Despite petrographic evidence of only minor weathering, two corestones (Oahu and Tecuamburro) have become enriched in REE 3+ relative to other lava flows from the same volcanoes, and display negative Ce anomalies. The exfoliated shells from these complexes tend to have lower concentrations of REE 3+, and have positive Ce anomalies. The fractionation of Ce from the other rare earth elements (REE) is inferred to be a manifestation of changes in the valence state of Ce from trivalent to tetravalent under oxidizing conditions. In settings where the development of corestone–shell complex is advanced, an acidic solution can mobilize trivalent REE, leach them out of more extensively weathered materials, and transport them to less acidic portions of the regolith undergoing incipient weathering. The precipitation of the REE 3+ in the rinds and centers of the corestones are likely due to increases of the pH of the weathering solution. Systematic weathering-induced REE behavior (enrichment of most REE, with lesser Ce enrichment resulting in a negative Ce anomaly) can be discerned even in corestone samples that exhibit major element abundances and petrographic features otherwise similar to unweathered basalts and andesites.

Changes in trace element composition of developing barley grain

SummaryChanges in the amounts of the trace elements iron, zinc, manganese and copper, present in intact grain, endosperm, testa pericarp and embryo throughout the developmental period were recorded. Accumulation of iron and zinc in intact grain was extremely rapid, rising in the case of iron from 40 ng/grain to 1600 ng/grain between 5 and 40 days after anthesis. Manganese accumulated steadily throughout, reaching a final value of 475 ng/grain. Significant amounts of copper were present throughout and a small peak was observed at 38 days after anthesis. Some variation from this overall pattern was found in the different morphological parts as development proceeded. This was notable in the case of embryo manganese, which was undetectable until 45 days after anthesis, when levels rose dramatically to reach a steady maximum of around 100 ng/embryo. The results are discussed in relation to the biochemical events accompanying maturation.