Abstract
Dynamic models of solar system evolution suggest that D-type asteroids formed beyond Saturn's orbit and represent invaluable witnesses of the prevailing conditions in the outer solar system. ...Here, we report a comprehensive petrographic and isotopic characterization of the carbonaceous chondrite Tarda, a recent fall recovered in the Moroccan Sahara. We show that Tarda shares strong similarities with the D-type-derived chondrite Tagish Lake, implying that Tarda represents a rare sample of D-type asteroids. Both Tarda and Tagish Lake are characterized by the presence of rare
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O-rich chondrules and chondrule fragments, high C/H ratios, and enrichments in deuterium,
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N, and
13
C. By combining our results with literature data on carbonaceous chondrites related to C-type asteroids, we show that the outer solar system 4.56 Gy ago was characterized by large-scale oxygen isotopic homogeneities in (i) the water–ice grains accreted by asteroids and (ii) the gas controlling the formation of FeO-poor chondrules. Conversely, the zone in which D-type asteroids accreted was significantly enriched in deuterium relative to the formation regions of C-type asteroids, features likely inherited from unprocessed, D-rich, molecular-cloud materials.
The determination of La and Ce anomalies in natural waters, biological samples and biogenic sedimentary rocks can provide unique information on biogeochemical processes in Earth surface environments. ...Over the last decades, several approaches have been used for calculating La/La* and Ce/Ce*, based on the comparison between measured and theoretical abundances (La* and Ce*) extrapolated from neighboring rare earth element concentrations normalized to chondritic or shale reference values. These extrapolations can be achieved either linearly or semi-logarithmically (“geometrically”), both methods being used in the literature in the absence of any consensus. We show here, using a database of rocks exhibiting no La and Ce anomaly, that the linear extrapolation of La and Ce abundances can result in markedly different results depending on whether chondritic or shale values are used for normalization. The geometric extrapolation allows consistent calculation of La and Ce anomalies for the entire compositional range tested in this study, regardless of whether data are normalized to chondritic or shale reference values. The differences between linear and geometric extrapolations are illustrated by a few selected examples from the literature, including various carbonate rock and seawater samples, further demonstrating that linear extrapolation can result in erroneous estimates of La and Ce anomalies. We thus propose that La/La* and Ce/Ce* ratios in all geological and environmental samples should be determined using the geometric extrapolation only.
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•La/La* and Ce/Ce* ratios calculated with linear and geometric extrapolations are compared.•Linear extrapolation can result in aberrant estimates of La and Ce anomalies.•La/La* and Ce/Ce* ratios should be determined using the geometric extrapolation only.
We report the first Ni and Cr stable isotope data for ureilite meteorites that are the mantle residue of a carbon‐rich differentiated planet. Ureilites have similar Ni stable isotope compositions as ...chondrites, suggesting that the core‐mantle differentiation of ureilite parent body (UPB) did not fractionate Ni isotopes. Since the size of Earth is potentially larger than that of UPB; with diameter >690 km), resulting in higher temperatures at the core‐mantle boundary of Earth, it can be predicted that the terrestrial core formation may not directly cause Ni stable isotope fractionation. On the other hand, we also report high‐precision Cr stable isotope composition of ureilites, including one ureilitic trachyandesite (ALM‐A) that is enriched in lighter Cr stable isotopes relative to the main‐group ureilites, which suggests that the partial melting occurred on UPB. The globally heavy Cr in the UPB compared to chondrites can be caused by sulfur‐rich core formation processes.
Plain Language Summary
The stable isotope fractionation of siderophile elements is robust to trace the planetary core formation processes. However, whether nickel (Ni) isotopes fractionate during the core formation is highly debated, since the origin of Ni stable isotope difference between bulk silicate Earth and chondrites is not clear. Here, we report high‐precision Ni stable isotope data (expressed as δ60/58Ni, the per mil deviation of Ni60/Ni58 ratios relative to NIST SRM 986) for ureilite meteorites that come from the mantle of a carbon‐rich differentiated body. Ureilites have an average δ60/58Ni value of 0.26 ± 0.13‰ (2SD, N = 22) that is highly consistent with that of chondrites with δ60/58Ni = 0.23 ± 0.14‰ (2SD, N = 37), which suggests that planetary core formation does not effectively fractionate Ni stable isotopes. There is a ureilite trachyandesite that enriches lighter Cr stable isotopes (δ53Cr = −0.11 ± 0.02‰; δ53Cr as the per‐mil deviation of Cr53/52Cr ratios relative to NIST SRM 979) relative to the main‐group ureilites (δ53Cr = −0.05 ± 0.04‰; 2SD, N = 10), which suggests that the partial melting occurred on ureilite parent body (UPB). The globally heavy Cr in the UPB compared to chondrites can be caused by sulfur‐rich core formation processes.
Key Points
Planetary magmatic processes do not fractionate Ni stable isotopes
Ureilite parent body (UPB) has similar δ60/58Ni values as chondrites, and Earth's core formation does not fractionate Ni stable isotopes
Cr stable isotopes recorded partial melting and sulfur‐rich core formation on UPB
Gadolinium-based contrast agents (GBCAs), routinely used in magnetic resonance imaging (MRI), end up directly in coastal seawaters where gadolinium concentrations are now increasing. Because many ...aquatic species could be sensitive to this new pollution, we have evaluated the possibility of using shellfish to assess its importance. Gadolinium excesses recorded by scallop shells collected in Bay of Brest (Brittany, France) for more than 30 years do not reflect the overall consumption in GBCAs, but are largely controlled by one of them, the gadopentetate dimeglumine. Although its use has been greatly reduced in Europe over the last ten years, gadolinium excesses are still measured in shells. Thus, some gadolinium derived from other GBCAs is bioavailable and could have an impact on marine wildlife.
The age of iron meteorites implies that accretion of protoplanets began during the first millions of years of the solar system. Due to the heat generated by
Al decay, many early protoplanets were ...fully differentiated with an igneous crust produced during the cooling of a magma ocean and the segregation at depth of a metallic core. The formation and nature of the primordial crust generated during the early stages of melting is poorly understood, due in part to the scarcity of available samples. The newly discovered meteorite Erg Chech 002 (EC 002) originates from one such primitive igneous crust and has an andesite bulk composition. It derives from the partial melting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis relative to the Sun's photosphere and at a high degree of melting of around 25%. Moreover, EC 002 is, to date, the oldest known piece of an igneous crust with a
Al-
Mg crystallization age of 4,565.0 million years (My). Partial melting took place at 1,220 °C up to several hundred kyr before, implying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets covered by andesitic crusts were probably frequent. However, no asteroid shares the spectral features of EC 002, indicating that almost all of these bodies have disappeared, either because they went on to form the building blocks of larger bodies or planets or were simply destroyed.
A major breakthrough in the field of rare earth element (REE) geochemistry has been the recent discovery of their utility to microbial life, as essential metalloenzymes catalyzing the oxidation of ...methanol to formaldehyde. Lanthanide-dependent bacteria are thought to be ubiquitous in marine and terrestrial environments, but direct field evidence of preferential microbial utilization of REE in natural systems is still lacking. In this study, we report on the REE and trace element composition of the tube of a siboglinid worm collected at a methane seep in the Gulf of Guinea; a tube-dwelling annelid that thrives in deep-sea chemosynthetic ecosystems. High-resolution trace element profiles along the chitin tube indicate marked enrichments of lanthanum (La) and cerium (Ce) in its oxic part, resulting in REE distribution patterns that depart significantly from the ambient seawater signature. Combined with various geochemical and microbiological evidence, this observation provides direct support for an active consumption of light-REE at cold seeps, associated with the aerobic microbial oxidation of methane. To further evaluate this hypothesis, we also re-examine the available set of REE data for modern seep carbonates worldwide. While most carbonate concretions at cold seeps generally display REE distribution patterns very similar to those for reduced pore waters in marine sediments, we find that seafloor carbonate pavements composed of aragonite commonly exhibit pronounced light-REE enrichments, as inferred from high shale-normalized La/Gd ratio (>~0.8), interpreted here as possibly reflecting the signature of lanthanide-dependent methanotrophic activity. This finding opens new perspectives for revisiting REE systematics in ancient seep carbonates and other microbialites throughout the Earth's history. In particular, the geochemical imprint of aerobic methane oxidation could be possibly traced using REE in Archaean stromatolites and other archives of Precambrian seawater chemistry, potentially providing new insights into the oxygenation of early Earth's oceans and associated microbiogeochemical processes.
In order to propose an optimal analytical procedure specific to ferromanganese (Fe–Mn) oxides, we investigated different modes of data acquisition using inductively coupled plasma mass spectrometry ...(ICP-MS). The results of trace element and Rare Earth Element (REE) determination in eight Fe–Mn nodules and crusts (FeMn-1, GSMC-1, GSMC-2, GSMC-3, GSPN-2, GSPN-3, NOD-A-1 and NOD-P-1) are presented here. The analytical procedure involves chemical dissolution of the Fe–Mn oxides and addition of a thulium (Tm) spike. The correction of measured values from potential isobaric interferences was investigated using both corrections based on mono-elemental solutions, and data acquisition in the high-resolution mode. The obtained results show that the high-resolution acquisition mode is unnecessary to achieve high quality data for REE in Fe–Mn oxides. Using our revised method, we provide a consistent set of precise and accurate values for eight widely used but poorly characterized certified reference materials.
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•Revised methodology for trace element characterization of Fe–Mn oxides by ICP-MS.•REE and trace element abundances were determined in low and high resolution modes.•LR presents better RSD than the HR acquisition mode (2.5% vs 6.5%).•HR is unnecessary to achieve high quality REE measurements for Fe–Mn oxides.•We provide new reference data on a set of eight Fe–Mn standards.
This paper summarizes the main guidelines for representing rare earth element (REE) abundance patterns, along with a review of the common mistakes or omissions that can alter REE plots and bias ...interpretations. It is specifically designed for ecotoxicologists and biologists, for whom the study of these elements has become an important field of research in recent years. Prior to applying REE diagrams to the study of living organisms, it is important to understand the rationale that led geochemists and cosmochemists to develop them. Used with the practical recommendations described here, these diagrams have the capacity to highlight fundamental processes taking place in the biosphere.
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•Rationale behind the use of REE normalization.•Misuse and common errors in drawing REE patterns.•REE patterns of living organisms show promising perspectives.
The Paris chondrite provides an excellent opportunity to study CM chondrules and refractory inclusions in a more pristine state than currently possible from other CMs, and to investigate the earliest ...stages of aqueous alteration captured within a single CM bulk composition. It was found in the effects of a former colonial mining engineer and may have been an observed fall. The texture, mineralogy, petrography, magnetic properties and chemical and isotopic compositions are consistent with classification as a CM2 chondrite. There are ∼45vol.% high-temperature components mainly Type I chondrules (with olivine mostly Fa0–2, mean Fa0.9) with granular textures because of low mesostasis abundances. Type II chondrules contain olivine Fa7 to Fa76. These are dominantly of Type IIA, but there are IIAB and IIB chondrules, II(A)B chondrules with minor highly ferroan olivine, and IIA(C) with augite as the only pyroxene. The refractory inclusions in Paris are amoeboid olivine aggregates (AOAs) and fine-grained spinel-rich Ca–Al-rich inclusions (CAIs). The CAI phases formed in the sequence hibonite, perovskite, grossite, spinel, gehlenite, anorthite, diopside/fassaite and forsterite. The most refractory phases are embedded in spinel, which also occurs as massive nodules. Refractory metal nuggets are found in many CAI and refractory platinum group element abundances (PGE) decrease following the observed condensation sequences of their host phases. Mn–Cr isotope measurements of mineral separates from Paris define a regression line with a slope of 53Mn/55Mn=(5.76±0.76)×106. If we interpret Cr isotopic systematics as dating Paris components, particularly the chondrules, the age is 4566.44±0.66Myr, which is close to the age of CAI and puts new constraints on the early evolution of the solar system. Eleven individual Paris samples define an O isotope mixing line that passes through CM2 and CO3 falls and indicates that Paris is a very fresh sample, with variation explained by local differences in the extent of alteration. The anhydrous precursor to the CM2s was CO3-like, but the two groups differed in that the CMs accreted a higherproportion of water. Paris has little matrix (∼47%, plus 8% fine grained rims) and is less altered than other CM chondrites. Chondrule silicates (except mesostasis), CAI phases, submicron forsterite and amorphous silicate in the matrix are all well preserved in the freshest domains, and there is abundant metal preserved (metal alteration stage 1 of Palmer and Lauretta (2011)). Metal and sulfide compositions and textures correspond to the least heated or equilibrated CM chondrites, Category A of Kimura et al. (2011). The composition of tochilinite–cronstedtite intergrowths gives a PCP index of ∼2.9. Cronstedtite is more abundant in the more altered zones whereas in normal highly altered CM chondrites, with petrologic subtype 2.6–2.0 based on the S/SiO2 and ∑FeO/SiO2 ratios in PCP or tochilinite–cronstedtite intergrowths (Rubin et al., 2007), cronstedtite is destroyed by alteration. The matrix in fresh zones has CI chondritic volatile element abundances, but interactions between matrix and chondrules occurred during alteration, modifying the volatile element abundances in the altered zones. Paris has higher trapped Ne contents, more primitive organic compounds, and more primitive organic material than other CMs. There are gradational contacts between domains of different degree of alteration, on the scale of ∼1cm, but also highly altered clasts, suggesting mainly a water-limited style of alteration, with no significant metamorphic reheating.
We report on new trace element analyses of enstatite chondrites (ECs) to clarify their behavior during the metamorphism. During the transition from a type 3 to a type 5 or higher, silicates lose a ...large portion of their trace elements to sulfides. Our procedure allows us to obtain trace element abundances of the silicate fraction of an EC quite easily. The element patterns of these fractions (especially REE patterns) are quite different for EH and EL chondrites, and are furthermore dependent on the metamorphic grade. This procedure can be usefull to classify meteorites, in particular when the sulfides are altered. Applied to anomalous ECs, it allows direct recognition of the EH affinity of QUE 94204, and suggests that Zakłodzie, NWA 4301, and NWA 4799 derive from the same EH-like body of previously unsampled composition.
We have used the concentrations obtained on the silicate fractions of the most metamorphosed chondrites to discuss the chemical characteristics of the primitive mantles of reduced bodies of EH or EL affinity (i.e., after core segregation). Our data indicate that these mantles are very depleted in refractory lithophile elements (RLEs), particularly in rare earth elements (REEs), and notably show significant positive anomalies in Sr, Zr, Hf, and Ti. These estimates imply that the cores contain most of the REEs, U and Th of these bodies. Interestingly, the inferred primitive mantles of these reduced bodies contrast with that of the Earth. If the Earth accreted essentially from ECs, one would expect similar signatures to be preserved, which is not the case. This mismatch can be explained either by a later homogenization of the bulk silicate Earth, or alternatively, that the materials that were accreted were isotopically similar to ECs, but mineralogically different (i.e., oldhamite-free).
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