Earthworms native to the former mine site of Devon Great Consols (DGC), UK reside in soils highly contaminated with arsenic (As). These earthworms are considered to have developed a resistance to As ...toxicity. The mechanisms underlying this resistance however, remain unclear. In the present study, non-resistant, commercially sourced
Lumbricus terrestris were exposed to a typical DGC soil in laboratory mesocosms. The earthworms bio-accumulated As from the soil and incurred DNA-damage levels significantly above those observed in the control mesocosm (assessed using the Comet assay). A dose response was observed between DNA damage (% tail DNA) and As concentration in soil (control, 98, 183, 236, 324 and 436
mg
kg
−1). As-resistant earthworms (
Lumbricus rubellus,
Dendrodrilus rubidus and
L. terrestris) collected from contaminated soils at DGC (203 to 9025
mg
kg
−1 As) had also bio-accumulated high levels of As from their host soils, yet demonstrated low levels of DNA damage compared with earthworms from uncontaminated sites. The results demonstrate that the As-contaminated soils at DGC are genotoxic to non-native earthworms and much less so to earthworms native to DGC, thus providing further evidence of an acquired resistance to As toxicity in the native earthworms.
The analysis of oxygen isotope ratios (δ18O) in biogenic silica (e.g. diatoms, sponge spicules, phytoliths) is an increasingly utilised palaeoclimatic proxy for lakes and oceans, providing an ...alternative to carbonate δ18O. Currently, the problems associated with the cleaning and extraction of pure diatom silica, especially from lake sediments, may compromise the precision associated with δ18Odiatom records. This is because, despite improvements in cleaning techniques, it is still difficult to remove silica-containing contaminants (e.g. tephra, silts and clays) from biogenic silica. Where it has proved difficult to remove all the silica bearing contaminants from a sample, mass balance calculations involving point counting have been used, but these are inherently inaccurate as they only consider the surface area of the contaminant, rather than volume. The new method described here assesses the volume of contamination in each sample of biogenic silica by using major and trace element geochemistry, allowing the δ18O of the contamination to be removed from the biogenic silica δ18O value by linear mass balance. In this case, diatom silica was contaminated with tephra, however the method should also be applicable to other contaminants such as silts and clays.
Following the Svecofennian arc accretionary growth and extensive granitoid magmatism in the Transscandinavian Igneous Belt (TIB), new crustal growth occurred west of the TIB to form the Gothian ...orogen. An early stage is manifested by 1.69–1.65
Ga subduction-related magmatism in the Ätran Terrane. A second stage, forming an 140
km wide segment east of the Permian Oslo Rift, is recorded by three 1.66–1.59
Ga metamorphosed volcano-sedimentary units, exposed in the Horred, Åmål and Stora Le-Marstrand formations in the Idefjorden Terrane. The 1.66
Ga Horred Formation is dominated by felsic volcanics and has geochemical signatures indicative of formation in an island arc setting. In contrast, the lithologically similar volcanic sequences in the 1.61
Ga Åmål Formation have geochemical signatures consistent with a continental-margin setting. The 1.60–1.59
Ga Stora Le-Marstrand Formation is dominated by greywacke-type metasediments with subordinate metabasalts. These volcanics have markedly primitive trace element signatures and depleted Nd isotopic compositions, all consistent with their derivation in an oceanic island arc setting. The sediments document two provenances: a distal continental source and one with Nd isotopic compositions similar to the SLM volcanism. Many of the metasediments in the Stora Le-Marstrand formation have chemical signatures consistent with derivation from continental crust, suggesting that this volcanic arc developed in the vicinity of a continental massif, possibly in a setting similar to the Philippine Sea. Accretion of the Horred and Stora Le-Marstrand arc systems occurred prior to 1.61 and 1.59
Ga, respectively, and was followed by voluminous, ca 1.59
Ga calc-alkaline magmatism.
The Eksjö intrusion forms a major tonalitic body in the Oskarshamn-Jönköping belt (OJB), SE Sweden. This is a NW-SE unit of dominantly intermediate granitoid intrusions, bound by felsic rocks of the ...Transscandinavian Igneous Belt (TIB). Previous U-Pb data for the Eksjö tonalite (1754±10 Ma) implied that subduction-related magmatism occurred in SE Sweden during a period of time when other data required that such magmatism had already moved further west. New U-Pb zircon dating establishes that the Eksjö tonalite crystallised at 1823±2 Ma and that subduction-related, granitoid magmatism of the OJB occurred in the 1834-1823 Ma interval. Field observations and geochemistry implies fractional crystallisation in either a continental arc or a mature island arc system. Although major portions of the Eksjö intrusion are well preserved, it is cut by NW-trending shear zones attributed to block-related movements that remained active until at least 1.80 Ga. Available constraints for the OJB support models of recurring convergent-margin tectonism along the southwestern margin of Baltica between 1.85-1.82 Ga and, hence, prior to onset of voluminous TIB 1 magmatism (1.81-1.77 Ga). Such a scenario accounts for recurring deformation in SW Finland (1.84-1.80 Ga), broadly coeval deformation in south-central Sweden, and apparent steps in Moho depths between the OJB and the pre-1.85 Ga margin of Baltica.
Metamorphism is a major mechanism for the re-distribution of fluids and mass in the Earth's crust, with these processes most prominently highlighted by the occurrence of major gold resources within ...these terranes. However, although orogenic gold deposits have contributed over 20% of the global gold production, their origins remain controversial. The nitrogen concentration and isotopic composition of rocks and minerals are potentially powerful tracers of crustal metamorphism and mineralization, but there have been few detailed applications of this approach to date. Although nitrogen isotopes have recently been used to elucidate the source of fluids in some Neoarchean orogenic gold deposits and Proterozoic to Paleozoic mountain belts, due to their age and geological complexity of these terranes, major uncertainties as to the behavior of nitrogen remain. The Otago and Alpine Schists in the South Island of New Zealand comprise a large, comparatively young (<
190 Ma), metasedimentary belt with multiple generations of quartz
±
carbonate veins, some of which are mineralized with gold. A range of rocks, with little primary compositional variation, is exposed from unmetamorphosed protolith to high-grade amphibolites and as such they present an ideal laboratory to investigate the mobility of nitrogen and potential nitrogen isotopic fractionations during metamorphism and mineralization. Here we present nitrogen concentrations and isotopic analyses of whole rock samples and mica separates from a number of crustal transects through the Otago crust.
The range of δ
15N values for mica and whole rock samples from the schists spans 0.2 to 7.0‰, and the nitrogen concentration from 23 to 3483 ppm. Sample provenance and rock type have minimal influence on the nitrogen concentration and isotopic value, which appears to have been inherited from the original sedimentary kerogen. There is no systematic variation between metamorphic temperature and δ
15N or N concentration in micas, suggesting that there has been little discernible loss of
15N-depleted fluids from silicates with increasing metamorphic temperature. Comparison of fluid mobile alkali element (K, Rb and Cs), carbon and nitrogen whole rock concentrations, indicates that for the Otago and Alpine Schists, in rocks up to upper greenschist facies significant nitrogen remains hosted in phases other than micas, most likely poorly matured carbonaceous material. Samples from Macraes Flat, a major gold producer, have a similar range of δ
15N values to the host terrane, but show distinctly higher nitrogen concentrations relative to unmineralized samples, due to the incorporation of nitrogen from the mineralizing hydrothermal fluid. This suggests that there is only a subtle metamorphic re-distribution of nitrogen during mineralization, albeit with minimal isotopic fractionation. In the case of nitrogen at least, the isotopic signatures of mineralized rocks support a metamorphic fluid source, and are inconsistent with mantle or meteoric fluid reservoirs. However, due to the high relative abundance of nitrogen in sedimentary rocks compared to other potential reservoirs, unless fluid fluxes are very large and well channeled, nitrogen signatures are not sensitive recorders of fluid inputs from mantle, magmatic or meteoric reservoirs. Conversely, the absence of a “sedimentary”-source nitrogen isotope signature similar to the host rock in an orogenic deposit would be a very strong indicator of an external, exotic source for the mineralizing fluids.
The relationship between the total arsenic concentration and the chemical speciation of arsenic in two species of earthworm (Lumbricus rubellus and Dendrodrilus rubidus) in relation to the host soil, ...was investigated for 13 sites of varying arsenic content, including a background level garden soil and a former mine site at the Devon Great Consols, UK. Earthworms were collected with the host soil (As soil concentration range 16-12, 466 mg kg(-1) dry weight) and measured for their total arsenic (concentration range 7-595 mg kg(-1) dry weight) using inductively coupled plasma mass spectrometry (ICP-MS). A methanol-water mixture was used to extract arsenic species from the earthworms prior to determination of the individual arsenic species by a combination of anion and cation exchange high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). A gradient elution anion exchange method is presented whereby nine arsenic species could be measured in one sample injection. Arsenic species were identified by comparison of retention times and sample spiking with known standards and a fully characterised seaweed extract. Arsenic was generally present in the earthworm as arsenate (As(V)) or arsenite (As(III)) and arsenobetaine (AB). Methylarsonate (MA), dimethylarsinate (DMA) and three arsenosugars (glycerol, phosphate, sulfate) were present as minor constituents. These results are discussed in relation to the mechanisms for coping with exposure to soil bound arsenic.
Mineralogical, chemical, and isotopic (O, C, S, and Sr) analyses were performed on minerals and bulk rocks from a forearc basement section to understand alteration processes and compare with ...mid‐ocean ridges (MOR) and ophiolites. Ocean Drilling Program Hole 786B in the Izu‐Bonin forearc penetrates 103 m of sediment and 725 m into volcanic flows, breccias, and basal dikes. The rocks comprise boninites and andesites to rhyolites. Most of the section was affected by low‐temperature (<100°C) seawater alteration, with temperatures increasing downward. The rocks are partly (5–25%) altered to smectite, Fe‐oxyhydroxide, calcite, and phillipsite, and exhibit gains of K, Rb, and P, loss of Ca, variable changes in Si, Na, Mg, Fe, Sr, and Y, and elevated δ18O and 87Sr/86Sr. Higher temperatures (∼150°C) in the basal dikes below 750 m led to more intense alteration and formation of chlorite‐smectite, corrensite, albite, K‐feldspar, and quartz (±chlorite). A 5 m thick hydrothermally altered and pyritized zone at 815 m in the basal dikes reacted with mixtures of seawater and hydrothermal fluids to Mg‐chlorite, albite, and pyrite, and gained Mg and S and lost Si and Ca. Focused flow of hydrothermal fluids produced serialization halos (Na‐K sericite, quartz, pyrophyllite, K‐feldspar, and pyrite) along quartz veins at temperatures of 200°–250°C. High 87Sr/86Sr ratios of chloritized (∼0.7055) and sericitized (∼0.7065) rocks indicate involvement of seawater via mixing with hydrothermal fluids. Low δ34S of sulfide (−2 to −5.5‰) and sulfate (12.5‰) are consistent with input of magmatic SO2 into hydrothermal fluids and disproportionation to sulfide and sulfate. Alteration processes were generally similar to those at MORs, but the arc section is more intensively altered, in part because of the presence of abundant glassy rocks and mafic phases. The increase in alteration grade below 750 m and the mineralization in the basal dikes are analogous to changes that occur near the base of the volcanic section in MOR and the Troodos ophiolite.
Lamb, A. L., Brewer, T. S., Leng, M. J., Sloane, H. J., Lamb, H. F. (2007). A geochemical method for removing the effect of tephra on lake diatom oxygen isotope records. Journal of Paleolimnology, ...37(4), 499-516.
The analysis of oxygen isotope ratios (d18O) in biogenic silica (e.g. diatoms, sponge spicules, phytoliths) is an increasingly utilised palaeoclimatic proxy for lakes and oceans, providing an alternative to carbonate d18O. Currently, the problems associated with the cleaning and extraction of pure diatom silica, especially from lake sediments, may compromise the precision associated with d18Odiatom records. This is because, despite improvements in cleaning techniques, it is still difficult to remove silicacontaining contaminants (e.g. tephra, silts and clays) from biogenic silica. Where it has proved difficult to remove all the silica bearing contaminants from a sample, mass balance calculations involving point counting have been used, but these are inherently inaccurate as they only consider the surface area of the contaminant, rather than volume. The new method described here assesses the volume of contamination in each sample of biogenic silica by using major and trace element geochemistry, allowing the d18O of the contamination to be removed from the biogenic silica d18O value by linear mass balance. In this case, diatom silica was contaminated with tephra, however the method should also be applicable to other contaminants such as silts and clays.
PDF
