Ion Microprobe Analyses Research Articles

Investigation of the Geochemical Preservation of ca. 3.0 Ga Permineralized and Encapsulated Microfossils by Nanoscale Secondary Ion Mass Spectrometry.

Observations of Archean organic-walled microfossils suggest that their fossilization took place through both encapsulation and permineralization. In this study, we investigated microfossils from the ca. 3.0 Ga Farrel Quartzite (Pilbara, Western Australia) using transmitted light microscopy, scanning electron microscopy, Raman microspectrometry, and nanoscale secondary ion mass spectrometry (NanoSIMS) ion microprobe analyses. In contrast to previous studies, we demonstrated that permineralized microfossils were not characterized by the micrometric spatial relationships between Si and C-N as observed in thin sections. Permineralized microfossils are composed of carbonaceous globules that did not survive the acid treatment, whereas encapsulated microfossils were characterized due to their resistance to the acid maceration procedure. We also investigated the microscale relationship between the 12C14N- and 12C2- ion emission as a proxy of the N/C atomic ratio in both permineralized and encapsulated microfossils. After considering any potential matrix and microtopography effects, we demonstrate that the encapsulated microfossils exhibit the highest level of geochemical preservation. This finding shows that the chemical heterogeneity of the microfossils, observed at a spatial resolution of a few hundreds of micrometers, can be related to fossilization processes. Key Words: Carbonaceous matter—Farrel Quartzite—Fossilization—NanoSIMS—Nitrogen—Permineralization. Astrobiology 17, 1192–1202.

Microbial structures and possible bacterial sulfide fossils in the giant Jinding Zn-Pb deposit, Yunnan, SW-China: Insights into the genesis of Zn-Pb sulfide mineralization

The Jinding Zn-Pb sulfide deposit, Lanping, Yunnan, China, is one of the youngest sediment-hosted giant Zn-Pb deposit in the world. It is also a well known deposit in China. The large scale of the mineralization and especially the huge volume of H2S that was required to precipitate the Zn-Pb sulfide are of great interest to ore geologists. Ore microscopy shows microbial structures such as framboidal sphalerite, spherical aggregates of galena-sphalerite, oolite sphalerite, dendritic colloidal sphalerite-pyrite, metacolloidal sphalerite-pyrite, multinuclear-metacolloidalring-like sphalerite-pyrite, botryoidal sphalerite-pyrite, framboidal pyrite and bacterial plate-like of galena-sphalerite. Detailed observations and analyses of the microbial structures at micron to nanometer scales by field emission scanning electron microscopy (FESEM) and energy dispersive spectrometry (EDS) reveal that the bacteria fossils are composed of sphalerite, galena or pyrite or of multiple sulfide minerals with calcite and that they are distributed in bacterial colonies in the ore. The individual bacteria fossils are spherical, botryoidal or ring-like with a diameter of 200–500 nm. Filamentous, mucoid and tubular extracellular polymeric substances (EPS) are commonly observed that are closely associated with, and have the same composition as, the bacteria fossils. Secondary ion microprobe analysis (SIMS) by in situ sulfur micro-isotopic analysis of the microbial sulfide structures and bacteria fossils yield δ34SV-CDT values varying from −48.6 to−9.5 per mil, indicating that there was a high percentage of sulfate reducing bacteria in the Zn-Pb sulfide mineralization process. Previous analyses have shown that the Zn-Pb mineralization was formed at a shallow depth and low temperature with barely visible hydrothermal alteration, the presence of evaporitic sulfate layers and paleo-oil reservoir characteristics. The authors believe that bacterial sulfate reduction might be the key H2S production mechanism in the Jinding dome that was required to form this giant Pb-Zn sulfide ore body.

Assessment of crystallographic orientation effects on secondary ion mass spectrometry (SIMS) analysis of cassiterite

Crystallographic orientation effects on ion microprobe analyses for U-Pb and O-isotopes have been reported for a number of oxide minerals, including rutile (TiO2) and baddeleyite (ZrO2). Here we evaluate the effects of crystal orientation on U-Pb and O-isotopic data measured by ion microprobe on cassiterite (SnO2), which is isostructural with rutile. The crystallographic orientations of mounted and polished grains of cassiterite were determined by electron backscatter diffraction (EBSD). Those grains were then analysed for U-Th-Pb isotopes and 18O/16O compositions using the SHRIMP RG and SHRIMP SI ion microprobes, respectively. Based on these data, cassiterite appears to show no dependence of key measurement parameters such as UO2/UO, Pb/UO, or 18O/16O ratios at the achieved precision with crystallographic orientation. The contrasting behaviour of isostructural cassiterite and rutile provides new insights into the mechanisms leading to crystallographic orientation effects during ion microprobe analyses with electronic structure proposed as being a significant factor.

Primary melt and fluid inclusions in regenerated crystals and phenocrysts of olivine from kimberlites of the Udachnaya-East Pipe, Yakutia: The problem of the kimberlite melt

The primary melt and fluid inclusions in regenerated zonal crystals of olivine and homogeneous phenocrysts of olivine from kimberlites of the Udachnaya-East pipe, were first studied by means of microthermometry, optic and scanning electron microscopy, electron and ion microprobe analysis (SIMS), inductively coupled plasma mass-spectrometry (ICP MSC), and Raman spectroscopy. It was established that olivine crystals were regenerated from silicate–carbonate melts at a temperature of ~1100°C.

The production rate of cosmogenic deuterium at the Moon's surface

The hydrogen (D/H) isotope ratio is a key tracer for the source of planetary water. However, secondary processes such as solar wind implantation and cosmic ray induced spallation reactions have modified the primordial D/H signature of ‘water’ in all rocks and soils recovered on the Moon. Here, we re-evaluate the production rate of cosmogenic deuterium (D) at the Moon's surface through ion microprobe analyses of hydrogen isotopes in olivines from eight Apollo 12 and 15 mare basalts. These in situ measurements are complemented by CO2 laser extraction-static mass spectrometry analyses of cosmogenic noble gas nuclides (3He, 21Ne, 38Ar). Cosmic ray exposure (CRE) ages of the mare basalts, derived from their cosmogenic 21Ne content, range from 60 to 422 Ma. These CRE ages are 35% higher, on average, than the published values for the same samples. The amount of D detected in the olivines increases linearly with increasing CRE ages, consistent with a production rate of (2.17±0.11)×10−12 mol(g rock)−1 Ma−1. This value is more than twice as high as previous estimates for the production of D by galactic cosmic rays, indicating that for water-poor lunar samples, i.e., samples with water concentrations ≤50 ppm, corrected D/H ratios have been severely overestimated.

Hydrogen isotope fractionation in methane plasma

The hydrogen isotope ratio (D/H) is commonly used to reconstruct the chemical processes at the origin of water and organic compounds in the early solar system. On the one hand, the large enrichments in deuterium of the insoluble organic matter (IOM) isolated from the carbonaceous meteorites are interpreted as a heritage of the interstellar medium or resulting from ion-molecule reactions taking place in the diffuse part of the protosolar nebula. On the other hand, the molecular structure of this IOM suggests that organic radicals have played a central role in a gas-phase organosynthesis. So as to reproduce this type of chemistry between organic radicals, experiments based on a microwave plasma of CH4 have been performed. They yielded a black organic residue in which ion microprobe analyses revealed hydrogen isotopic anomalies at a submicrometric spatial resolution. They likely reflect differences in the D/H ratios between the various CHx radicals whose polymerization is at the origin of the IOM. These isotopic heterogeneities, usually referred to as hot and cold spots, are commensurable with those observed in meteorite IOM. As a consequence, the appearance of organic radicals in the ionized regions of the disk surrounding the Sun during its formation may have triggered the formation of organic compounds.

Ion microprobe analyses of carbon in Fe–Ni metal in iron meteorites and mesosiderites

Carbon concentrations in kamacite, taenite, and plessite (kamacite-taenite intergrowths) were measured in 18 iron meteorites and 2 mesosiderites using the Cameca ims 1280 ion microprobe at the University of Hawai‘i with a 5–7μm beam and a detection limit of <1ppm. Our goal was to investigate the effects of carbon on the microstructure of iron meteorites during cooling and to evaluate how carbon partitions between metal phases and other carbon-bearing minerals (graphite, haxonite, cohenite) in various meteorite groups. Carbon concentrations range from ∼100 to ∼1000ppm in taenite and plessite in groups IAB, IIICD, and IIIAB, which contain graphite and/or carbides, but only 2–6ppm in groups IVA, IVB and the ungrouped iron, Tishomingo, which lack graphite and carbides. Carbon contents in kamacite range from ∼2 to ∼10ppm in most studied meteorites, including IIAB, but higher abundances were found in kamacite from IAB Pitts subgroup meteorites Pitts and Woodbine (12–15ppm). Our carbon abundances for kamacite are lower than most published ion probe data, indicating that earlier carbon measurements had contamination problems.Grains of taenite and fine-grained plessite in carbon-rich meteorites, which all have normal M-shaped nickel profiles due to slow cooling, have diverse carbon contents and zoning profiles. This is because taenite decomposed by diverse mechanisms over a range of temperatures, when nickel could only diffuse over sub-μm distances. Carbon diffusion through taenite to growing carbides was rapid at the upper end of this temperature range, but was very limited at the lower end of the temperature range. In mesosiderites, carbon increases from 12ppm in tetrataenite to 40–115ppm in cloudy taenite as nickel decreases from 50% to 35%. Low carbon levels in tetrataenite may reflect ordering of iron and nickel; higher carbon in cloudy taenite is attributed to metastable bcc phase, possibly martensite, with ∼300ppm carbon intergrown with tetrataenite. Pearlitic plessite, which only forms in carbon-rich irons, contains much less carbon than martensitic plessite: 10–20ppm and 300–500, respectively, in IAB irons. Pearlitic plessite consists of μm-scale intergrowths of low-nickel kamacite and tetrataenite, which formed during cooling from ∼450 to 300°C when haxonite was forming. Martensitic plessite decomposed to tetrataenite and metastable high-nickel kamacite at temperatures below 300°C, which depended on nickel content. Carbon accumulated in untransformed taenite when haxonite growth ceased, producing M-shaped carbon profiles.Bulk carbon concentrations inferred from our ion probe data are 3–4ppm in IVA, IVB, and Tishomingo, which has IVB-like depletions of moderately volatile siderophiles. Published bulk carbon contents of IVA and IVB irons are >10 times higher suggesting contamination problems. Our ion probe analyses and observations of carbide and graphite show that bulk carbon decreases with decreasing germanium and other moderately volatile elements from group IAB, through IIAB and IIIAB, to group IVA and IVB. These trends may have been inherited from fractionated chondritic precursors, or may have been produced by impacts that caused volatile loss, separation of mantle from core material, and relatively rapid cooling of irons poor in volatiles and carbon.

Matrix effects on the relative sensitivity factors for manganese and chromium during ion microprobe analysis of carbonate: Implications for early Solar System chronology

The short-lived radionuclide 53Mn decays to 53Cr providing a relative chronometer for dating the formation of Mn-rich minerals in meteorites. Secondary ion mass spectrometry (SIMS) has been extensively used for in situ dating of meteoritic olivine and carbonate by the 53Mn–53Cr system, however a significant analytical challenge has been realising accurate measurements of the Mn/Cr ratio in individual minerals of differing chemical compositions. During SIMS analysis, elements are ionised with differing efficiencies and standard materials are required to calibrate measured ion intensities in terms of relative elemental concentrations. The carbonate system presents a particular analytical difficulty since such standards are not naturally available due to low and variable Cr contents. Here, we utilise ion implantation of Cr into carbonate and other phases to accurately determine the relative sensitivity factors of Mn/Cr during SIMS analysis. We find significant variations in Mn/Cr RSF values among different carbonate minerals that depend systematically on chemical composition and we propose an empirical correction scheme that quantitatively yields an accurate RSF for carbonates of diverse chemical compositions. Correction of SIMS carbonate data for this strong matrix effect may help to reconcile some outstanding problems regarding the timescales of aqueous alteration processes in carbonaceous chondrites. Mn–Cr ages, revised based our new understanding of the matrix effect, are, in general, earlier than previously thought and the duration of carbonate formation is shorter.

Oxo-mangani-leakeite from the Hoskins mine, New South Wales, Australia: occurrence and mineral description

AbstractOxo-mangano-leakeite, a newly approved end-member of the amphibole supergroup (IMA-CNMNC 20150-35), has been found in a rock containing manganese silicate and oxide at the Hoskins Mine, a Mn deposit 3 km west of Grenfell, New South Wales. The end-member formula of oxo-mangani-leakeite is ANaBNa2C(Mn3+4Li)TSi8 O22WO2, which would require SiO2 53.15, Mn2O3 34.91, Li2O 1.66, Na2O 10.28, total 100.00 wt.%. The empirical formula derived for the sample of this work from electron and ion microprobe analysis using constraints resulting from single-crystal structure refinement is A(Na0.65K0.36)∑ = 1.01B(Na1.94Ca0.06)∑ = 2.00C(Mg1.60Zn0.01 Li0.58)∑ = 5.01T(Si7.98Al0.02)∑ = 8.00O22W(O1.34OH0.66)∑ = 2.00. Oxo-mangano-leakeite is biaxial (–), with α = 1.681, β = 1.712, γ = 1.738, all ± 0.002, and 2V (meas.) = 81.0(4)°, 2V (calc.) = 83.5°. The unit-cell dimensions are a = 9.875(5), b = 17.873(9), c = 5.295(2) Å, β = 104.74(3)°, V = 903.8 (7) Å3; the space group is C2/m, with Z = 2. The strongest ten reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 8.423, 100, (110); 3.377, 46, (131); 4.461, 40, (040); 4.451, 40, (021); 3.134, 37, (310); 2.694, 37, (151); 2.282, 27, (); 2.734, 25, (31); 2.575, 24, (061); 2.331, 24, [() ()]. The holotype material is deposited in the Canadian Museum of Nature, Ottawa, under the catalogue number CMNMC 86895.

Order of [6]Ti4+ in a Ti-rich calcium amphibole from Kaersut, Greenland: a combined X-ray and neutron diffraction study

In order to characterize the role of Ti in the crystal structure of calcium amphiboles with high or even dominant oxo-component, the crystal structure of a Ti-rich calcium amphibole from a gabbro at Kaersut, Greenland, has been refined with single-crystal MoKα X-ray intensity data to an R 1(F) index of ~0.025, and with single-crystal Laue neutron intensity data to an R 1(F) index of ~0.053. The crystal used for X-ray structure refinement was characterized by electron- and ion-microprobe analysis. The site populations of the C-group cations Mg, Fe and Ti were calculated from the refined site-scattering values for the M(1), M(2) and M(3) sites derived by both X-ray and neutron diffraction. Ti is distributed among all the three sixfold coordinated M sites, with a strong preference for the M(1) and M(3) sites, where its main role is maintaining electroneutrality at the deprotonated O(3) site. The pattern of distortion of the M(1), M(2) and M(3) octahedra differs from that in F-free deprotonated or partly deprotonated amphiboles, where Ti4+ does not occur at the M(3) site. The neutron structure refinement provides also a clear picture of the environment of the proton, anisotropic displacement behaviour and potential hydrogen-bonding arrangements. A trifurcated hydrogen-bonding configuration has been identified, with two O(6) and one O(7) oxygen atoms as acceptors of weak hydrogen-bonds.

White mica trace element and boron isotope evidence for distinctive infiltration events during exhumation of deeply subducted continental crust

ABSTRACTPrevious study of subducted continental crust within the Luliang Shan terrane in Northwest China has documented metasomatic formation of thick, hydrated phengite + garnet-rich selvages at the interface between mafic eclogite blocks and quartzofeldspathic host gneiss. Whole rock concentrations of Cs and Ba within the selvage are enriched by two orders of magnitude relative to the eclogite blocks and host gneiss. We performed in situ ion microprobe analyses of Li, Be, B, Rb, Sr, Cs and Ba and δ11B of phengite within the Luliang Shane terrane to better constrain the source(s) of the infiltrating fluid. The phengite within the selvage are enriched in Li, Cs and Ba and yield δ11B values between −30‰ and −9‰, values that are lower than mantle values. High Ba/Rb, Cs/Rb coupled with low B/Be, B/Li and highly negative δ11B values indicate that the high-pressure fluid that formed the selvage was derived from highly devolatilized rocks within the subduction channel. In contrast, muscovite, which crystallized in the adjacent host gneiss during a subsequent lower pressure phase of fluid infiltration at approximately 0.9 GPa depths, has much lower Li, Cs and Ba relative to the high-pressure phengite. These retrograde muscovite have very high concentrations of B (up to 5500 ppm) and Be (up to 50 ppm) and high (−2 to +8‰) δ11B values that are consistent with crystallization from a fluid derived from shallower and less devolatilized regions of the subduction zone. Additional host gneiss samples, regionally distributed and kilometres away from the studied area lack the B-rich signature and indicate that the late stage fluids were likely localized to the region near the studied traverse.

Genesis and mechanisms of formation of rare-metal peralkaline granites of the Khaldzan Buregtey massif, Mongolia: Evidence from melt inclusions

Melt inclusions were studied by various methods, including electron and ion microprobe analysis, to determine the compositions of melts and mechanisms of formation of rare-metal peralkaline granites of the Khaldzan Buregtey massif in Mongolia. Primary crystalline and coexisting melt inclusions were found in quartz from the rare-metal granites of intrusive phase V. Among the crystalline inclusions, we identified potassium feldspar, albite, tuhualite, titanite, fluorite, and diverse rare-metal phases, including minerals of zirconium (zircon and gittinsite), niobium (pyrochlore), and rare earth elements (parisite). The observed crystalline inclusions reproduce almost the whole suite of major and accessory minerals of the rare-metal granites, which supports the possibility of their crystallization from a magmatic melt. Melt inclusions in quartz from these rocks are completely crystallized. Their daughter mineral assemblage includes quartz, microcline, aegirine, arfvedsonite, polylithionite, a zirconosilicate, pyrochlore, and a rare-earth fluorocarbonate. The melt inclusions were homogenized in an internally heated gas vessel at a temperature of 850°C and a pressure of 3 kbar. After the experiments, many inclusions were homogeneous and consisted of silicate glass. In addition to silicate glass, some inclusions contained tiny quench zircon crystals confined to the boundary of inclusions, which indicates that the melts were saturated in zircon. In a few inclusions, glass coexisted with a CO2 phase. This allowed us to estimate the content of CO2 in the inclusion as 1.5 wt %. The composition of glasses from the homogeneous melt inclusions is similar to the composition of the rare-metal granites, in particular, with respect to SiO2 (68–74 wt %), TiO2 (0.5–0.9 wt %), FeO (2.2–4.6 wt %), MgO (0.02 wt %), and Na2O + K2O (up to 8.5 wt %). On the other hand, the glasses of melt inclusions appeared to be strongly depleted compared with the rocks in CaO (0.22 and 4 wt %, respectively) and Al2O3 (5.5–7.0 and 9.6 wt %, respectively). The agpaitic index is 1.1–1.7. The melts contain up to 3 wt % H2O and 2–4 wt % F. The trace element analysis of glasses from homogenized melt inclusions in quartz showed that the rare-metal granites were formed from extensively evolved rare-metal alkaline melts with high contents of Zr, Nb, Th, U, Ta, Hf, Rb, Pb, Y, and REE, which reflects the metallogenic signature of the Khaldzan Buregtey deposit. The development of unique rare metal Zr–Nb–REE mineralization in these rocks is related to the prolonged crystallization differentiation of melts and assimilation of enclosing carbonate rocks.

Origin of the eclogitic clasts with graphite-bearing and graphite-free lithologies in the Northwest Africa 801 (CR2) chondrite: Possible origin from a Moon-sized planetary body inferred from chemistry, oxygen isotopes and REE abundances

In order to clarify the origin of the eclogitic clasts found in the NWA801 (CR2) chondrite (Kimura et al., 2013), especially, that of the high pressure and temperature (P–T) condition (∼3GPa and ∼1000°C), we conducted ion microprobe analyses of oxygen isotopes and rare earth element (REE) abundances in the clasts. Oxygen isotopic compositions of the graphite-bearing lithology (GBL) and graphite-free lithology (GFL) show a slope ∼0.6 correlation slightly below the CR-CH-CB chondrites field in the O three-isotope-diagram, with a large variation for the former and almost homogeneous composition for the latter. The average REE abundances of the two lithologies show almost unfractionated patterns. Based on these newly obtained data, as well as mineralogical observations, bulk chemistry, and considerations about diffusion timescales for various elements, we discuss in detail the formation history of the clasts. Consistency of the geothermobarometers used by Kimura et al. (2013), suggesting equilibration of various elements among different mineral pairs, provides a strong constraint for the duration of the high P–T condition. We suggest that the high P–T condition lasted 102–103years. This clearly precludes a shock high pressure (HP) model, and hence, strongly supports a static HP model. A static HP model requires a Moon-sized planetary body of ∼1500km in radius. Furthermore, it implies two successive violent collisions, first at the formation of the large planetary body, when the clasts were placed its deep interior, and second, at the disruption of the large planetary body, when the clasts were expelled out of the parent body and later on transported to the accretion region of the CR chondrites. We also discuss possible origin of O isotopic variations in GBL, and presence/absence of graphite in GBL/GFL, respectively, in relation to smelting possibly occurred during the igneous process(es) which formed the two lithologies. Finally we present a possible formation scenario of the eclogitic clasts.

REDISTRIBUTION OF ALKALINE ELEMENTS IN ASSOCIATION WITH AQUEOUS ACTIVITY IN THE EARLY SOLAR SYSTEM

It is known that the Sayama meteorite (CM2) shows an extensive signature for aqueous alteration on the meteorite parent body, and that most of the primary minerals in the chondrules are replaced with phyllosilicates as the result of the aqueous alteration. In this paper, it is confirmed from the observation of two-dimensional Raman spectra that a part of olivine in a chondrule collected from the Sayama chondrite is serperntinized. Ion microprobe analysis of the chondrule showed that alkaline elements such as Rb and Cs are heterogeneously redistributed in the chondrule. The result of higher Rb and Cs contents in serpentinized phases in the chondrule rather than in other parts suggested the selective adsorption of alkaline elements into the serpentine in association with early aqueous activity on the meteorite parent body. Furthermore Ba isotopic analysis provided variations of 135Ba/138Ba and 137Ba/138Ba in the chondrule. This result was consistent with our previous isotopic data suggesting isotopic evidence for the existence of the presently extinct nuclide 135Cs in the Sayama meteorite, but the abundance of 135Cs in the solar system remains unclear because of large analytical uncertainties.

Geochronology and geochemistry of rhyolites from Hormuz Island, southern Iran: A new record of Cadomian arc magmatism in the Hormuz Formation

Hormuz Island, a salt-gypsum dome in the Persian Gulf in southern Iran, is a complex halotectonic melange comprising evaporites, carbonates, volcanic and volcaniclastic rocks, as well as low-grade metamorphic and sedimentary rocks. Based on trace element (including rare earth elements REE) compositions of whole rocks and zircon, Hormuz rhyolites are inferred to have formed from subduction-related magmas generated in an active continental margin setting. Ion microprobe analyses of zircon crystals yielded concordant U–Pb ages with weighted mean 206Pb/238U age of 558±7Ma (juvenile zircons in contrast to those from previous magmatic episodes or xenocrysts) along with younger and older discordant ages which likely represent Pb loss and the presence of xenocrystic domains, respectively. Trace element ratios and in particular REE patterns of juvenile zircon from Hormuz rhyolites indicate crystallization from continental crustal source rocks typical for subduction environments. The concordant 206Pb/238U zircon age agrees with ages obtained from most other structural zones of Iran which indicate regional consolidation of igneous basement during the Neoproterozoic to Early Cambrian. Furthermore, Hormuz rhyolite ages and compositions correlate with counterparts that co-evolved along the northern margin of Gondwana, and are now preserved along the southern coast of the Persian Gulf. Hormuz rhyolites erupted synchronously with the deposition of carbonates and evaporites, suggesting that volcanism occupied an extensional backarc or retroarc setting. Such depositional environments predominated in the northern Gondwana continental margin where convergent (Proto-Tethyan) and extensional (Najd) tectonic regimes coexisted.

The Ranger uranium deposit, northern Australia: Timing constraints, regional and ore-related alteration, and genetic implications for unconformity-related mineralisation

The Ranger uranium deposit, northern Australia: Timing constraints, regional and ore-related alteration, and genetic implications for unconformity-related mineralisation

Approximate chemical analysis of volcanic glasses using Raman spectroscopy.

The effect of chemical composition on the Raman spectra of a series of natural calcalkaline silicate glasses has been quantified by performing electron microprobe analyses and obtaining Raman spectra on glassy filaments (~450 µm) derived from a magma mingling experiment. The results provide a robust compositionally‐dependent database for the Raman spectra of natural silicate glasses along the calcalkaline series. An empirical model based on both the acquired Raman spectra and an ideal mixing equation between calcalkaline basaltic and rhyolitic end‐members is constructed enabling the estimation of the chemical composition and degree of polymerization of silicate glasses using Raman spectra. The model is relatively insensitive to acquisition conditions and has been validated using the MPI‐DING geochemical standard glasses1 as well as further samples. The methods and model developed here offer several advantages compared with other analytical and spectroscopic methods such as infrared spectroscopy, X‐ray fluorescence spectroscopy, electron and ion microprobe analyses, inasmuch as Raman spectroscopy can be performed with a high spatial resolution (1 µm2) without the need for any sample preparation as a nondestructive technique. This study represents an advance in efforts to provide the first database of Raman spectra for natural silicate glasses and yields a new approach for the treatment of Raman spectra, which allows us to extract approximate information about the chemical composition of natural silicate glasses using Raman spectroscopy. We anticipate its application in handheld in situ terrestrial field studies of silicate glasses under extreme conditions (e.g. extraterrestrial and submarine environments). © 2015 The Authors Journal of Raman Spectroscopy Published by John Wiley & Sons Ltd

Boron isotopes in tourmaline from the ca. 3.7–3.8 Ga Isua supracrustal belt, Greenland: Sources for boron in Eoarchean continental crust and seawater

Boron is highly concentrated in Earth’s crust relative to primitive mantle. However, when present-day crustal concentrations were achieved remains debatable. It has been proposed that seawater boron δ11B was lower than at present, consistent with a model relating increase in sea-water δ11B to the proportion of B extracted from Earth’s mantle into the oceans and crust. Our in situ ion microprobe analyses of tourmaline in 17 samples from the Eoarchean Isua supracrustal belt, Southwest Greenland, gave the following average δ11B with uncertainties ranging from ±0.4 to ±1.9‰: δ11B=−7.1 to −11.5‰ in amphibolite; δ11B=−10.5 to −25.3‰ in mica schist; δ11B=−19.2‰ in metachert (one sample), and δ11B=−21.9‰ in metaconglomerate (one sample). Tourmaline is largely schorl–dravite, rarely uvite–feruvite, and shows color and compositional zoning. δ11B varies from grain to grain in most samples; grains in a kyanite–staurolite schist are isotopically zoned, possibly because the rims incorporated B released by muscovite breakdown. The patterns in color-zoned tourmaline grains in our samples are not consistent with detrital origin of the cores, which rules out the possibility of there being tourmaline detritus from pre-existing continental crust in the studied samples. The tourmaline-bearing rocks are found in both the ca. 3700Ma northern and ca. 3800Ma southern terranes in the Isua supracrustal belt. Following an approach suggested by Chaussidon and Appel, we estimated Eoarchean seawater δ11B by calculating back from δ11B of tourmaline in metasedimentary rocks using fractionation of boron isotopes between clays and muscovite, tourmaline and aqueous fluid. This calculation gave an estimated δ11B≈+14±15‰ for Eoarchean seawater, 25‰ lower than present-day seawater (δ11B=+39.5‰). For comparison, an estimate obtained simply by direct comparison of δ11B for Eoarchean and Phanerozoic tourmaline presumed to have crystallized in similar environments gives δ11B≈+30‰ for Eoarchean seawater.At first, our results appear to be contradictory. On the one hand, tourmaline is as widespread and abundant in the Isua supracrustal rocks as it is in many younger complexes, which suggests that extraction of boron from the mantle had reached levels close to present day levels. On the other hand, there is no evidence of boron having been extracted prior to ca. 3800Ma and a seawater δ11B lower than present-day δ11B=39.5‰ implies that extraction of B from the mantle had not reached the present-day extent. The proto-arc scenario proposed by A. Nutman and co-authors offers a possible resolution to the contradiction by considering the abundance and isotopic composition of B in the Isua supracrustal rocks as a localized phenomenon that should not be interpreted to reflect B concentrations in an Earth-circling ocean. Accumulation of boron in seawater in a partially isolated basin associated with a proto-arc and the attendant volcanism might have been sufficiently rapid for the needed concentrations to be attained in a relatively short time.

Shell growth, microstructure and composition over the development cycle of the European abalone Haliotis tuberculata

The shell of the European abalone Haliotis tuberculata is a model for studying mechanisms of mollusc shell formation, but the early steps of shell formation and calcification remain poorly documented. The microstructure and the mineralogical and geochemical composition of larval and juvenile shells were investigated by scanning electron microscopy, infrared spectroscopy and ion microprobe analyses (NanoSIMS). Analyses were performed on shells obtained from controlled fertilisations at the hatchery France-Haliotis (Plouguerneau, France) in July 2009 and 2010 using abalone from Roscoff. Shell cross sections revealed the microstructural arrangement of the developing shell, showing progressive biomineral organisation into two differentiated layers, i.e. the outer granular and the internal nacreous layer. Infrared analysis confirmed that the European abalone shell, at every stage of development, was mostly composed of CaCO3 in the form of aragonite. Variations in trace element composition, i.e. Sr/Ca, were measured in the different stages and correlated with micro-structural changes in the shells. Experimental manganese labelling of live abalones produced cathodoluminescence marks in the growing shell sections. The increase in shell thickness can be used to determine the growth rate of an early adult abalone shell.

Carbonate formation events in ALH 84001 trace the evolution of the Martian atmosphere

Carbonate minerals provide critical information for defining atmosphere-hydrosphere interactions. Carbonate minerals in the Martian meteorite ALH 84001 have been dated to ∼ 3.9 Ga, and both C and O-triple isotopes can be used to decipher the planet's climate history. Here we report Δ(17)O, δ(18)O, and δ(13)C data of ALH 84001 of at least two varieties of carbonates, using a stepped acid dissolution technique paired with ion microprobe analyses to specifically target carbonates from distinct formation events and constrain the Martian atmosphere-hydrosphere-geosphere interactions and surficial aqueous alterations. These results indicate the presence of a Ca-rich carbonate phase enriched in (18)O that formed sometime after the primary aqueous event at 3.9 Ga. The phases showed excess (17)O (0.7‰) that captured the atmosphere-regolith chemical reservoir transfer, as well as CO2, O3, and H2O isotopic interactions at the time of formation of each specific carbonate. The carbon isotopes preserved in the Ca-rich carbonate phase indicate that the Noachian atmosphere of Mars was substantially depleted in (13)C compared with the modern atmosphere.