Yangting Lin

ISOTOPIC ANALYSIS OF SUPERNOVA SiC AND Si3N4 GRAINS FROM THE QINGZHEN (EH3) CHONDRITE

We report Al-Mg, Ca, and Ti isotopic data in 16 silicon carbide grains and four silicon nitride grains from the Qingzhen enstatite chondrite. Previous C, N, and Si isotopic measurements had identified these grains as type X grains, believed to have an origin in Type II supernovae (SNe). The grains analyzed include both subtypes X1 and X2. Twelve SiC and three Si3N4 grains show evidence for initial 26Al, and eight SiC grains evidence for 44Ti; 11 SiC grains have 49Ti excesses, possibly indicating the initial presence of 49V. A correlation with subtype is shown for 44Ti: X2 grains that have the highest inferred 44Ti/48Ti ratios. A weaker correlation exists for N ratios: X2 grains with 12C/13C > 300 have higher 14N/15N ratios than X1 grains. We compare our data and data from previous reports with the SN models by Rauscher et al. The SN models can explain the C and N isotopic ratios fairly well if material from the 15N-rich spike in the He/N zone of the 25 M ☉ SN model is used. They also can explain the 44Ti/48Ti ratios of the X1 and X2 grains. For the latter, substantial contributions from the inner Ni core are required. They indicate that not for all grains the 49Ti excesses can be attributed to decay of 49V and material from the He/C zone, where 49Ti is produced by neutron capture, is needed. The SN models, however, fail in explaining the Si isotopic ratios of most of the grains in a satisfactory fashion and the distinction between X1 and X2 grains. They also fail in explaining the observed correlation between the 26Al/27Al ratios and 12C/13C (and 14N/15N) ratios.

Presolar Grains from the Qingzhen (EH3) Meteorite

A 28 g sample of the Qingzhen enstatite (EH3) chondrite was subjected to chemical and physical separation procedures to yield several grain-size residues. Ion mapping of isotopes of Si, O, and C in the ion microprobe of two size fractions (QZR4: 0.4-0.8 μm; QZR5: 0.8-2 μm) identified 55 30Si-depleted candidates out of 37,917 Si-rich grains and six 18O-depleted grains out of 54,410 oxides. Subsequent isotopic analyses of C, N, and Si of 48 grains of the 30Si-depleted candidates and additional randomly selected SiC and Si3N4 grains confirmed 36 of X-type SiC, nine of X-type Si3N4, and one of A+B-type SiC. The isotopic compositions of most X grains overlap those of previously measured X grains from the Murchison carbonaceous chondrite, but ~25% show more pronounced 29Si deficits, suggestive of multiple stellar origins of X grains. Presolar Si3N4 grains have isotopic compositions similar to those of X SiC grains, except that their C isotopic ratios are close to solar. The relative abundances of various presolar grain types in Qingzhen are different from those in Murchison, suggestive of heterogeneity and/or size sorting in the primitive solar nebula.

Volcanic history of the Imbrium basin: A close-up view from the lunar rover Yutu.

Significance After the Apollo and Luna missions, which were flown about 40 years ago, the Moon was explored only from orbit. In addition, no samples were returned from the young and high-FeO and TiO2 mare basalt in the northern Imbrium basin. Such samples are important to understand the formation and evolution of the Procellarum KREEP [potassium (K), rare earth elements (REE), and phosphorus (P)] terrain, a key terrain highly enriched in radioactive nuclides. The Chang’e-3 mission carried out the first in situ analyses of chemical and mineral compositions of the lunar soil and ground-based measurements of the lunar regolith and the underlying basalt units at this specific site. The lunar regolith layer recorded the surface processes of the Moon, whereas the basalt units recorded the volcanic eruption history. We report the surface exploration by the lunar rover Yutu that landed on the young lava flow in the northeastern part of the Mare Imbrium, which is the largest basin on the nearside of the Moon and is filled with several basalt units estimated to date from 3.5 to 2.0 Ga. The onboard lunar penetrating radar conducted a 114-m-long profile, which measured a thickness of ∼5 m of the lunar regolith layer and detected three underlying basalt units at depths of 195, 215, and 345 m. The radar measurements suggest underestimation of the global lunar regolith thickness by other methods and reveal a vast volume of the last volcano eruption. The in situ spectral reflectance and elemental analysis of the lunar soil at the landing site suggest that the young basalt could be derived from an ilmenite-rich mantle reservoir and then assimilated by 10–20% of the last residual melt of the lunar magma ocean.

Precise micrometre-sized Pb-Pb and U-Pb dating with NanoSIMS

We report a new method of Pb-Pb dating for zircon and baddeleyite with a lateral resolution of <2 μm and U-Pb dating for zircon with a lateral resolution of <5 μm using CAMECA NanoSIMS 50L. The O− primary beam was optimized to a current of ∼500 pA with a diameter of 1.7 μm. The zircon standard M257 and baddeleyite standard Phalaborwa were dated by the Pb-Pb method, yielding 207Pb/206Pb ages of 563 ± 14 Ma and 2058 ± 6 Ma, respectively. These results agree well with the recommended ages within analytical uncertainties. Four zircon standards, including Qinghu, Plesovice, Temora, and 91500 were dated by the U-Pb method. The samples were measured in a scanning mode by rastering 3 × 3 μm2 areas in order to eliminate pit depth-dependent U-Pb fractionation. The weighted average 206Pb/238U ages obtained by this method for the four zircon standards are 158 ± 3 Ma, 337 ± 7 Ma, 427 ± 10 Ma, and 1076 ± 14 Ma, respectively. These results are consistent with the reported ID-TIMS ages of these samples within error. Our study demonstrates that Pb-Pb ages of zircon and baddeleyite can be determined with a lateral resolution of <2 μm, and U-Pb ages of zircon can be measured with a lateral resolution of <5 μm by CAMECA NanoSIMS. This technique will have important applications to high lateral resolution dating, such as thin layers of zoned zircons, small grains of lunar zircon, and micron-sized baddeleyites in Martian meteorites and in various achondrites from differentiated asteroids.

Improved precision and spatial resolution of sulfur isotope analysis using NanoSIMS

High precision analyses of all four sulfur isotopes in four pyrite and three sphalerite standards and in working reference samples were carried out using a CAMECA NanoSIMS 50L instrument. The measurements were made using three different settings of the Faraday cup (FC) and/or electron multiplier (EM) detectors, which meet different requirements for spatial resolution. The effects of EM aging and quasi-simultaneous arrival were corrected before the calibration of instrumental mass fractionation by a standard–sample–standard bracket method using the standards measured together with the samples. High analytical precision was achieved by counting 32S, 33S and 34S with the FCs and 36S with the EM (i.e. the FC–FC–FC–EM mode) using a 0.7 μm diameter ∼350 pA Cs+ primary beam and scanning over areas of 5 × 5 μm2. The standard deviations of spot-to-spot and grain-to-grain (external reproducibility 1 SD) measurements were less than 0.3, 0.3 and 0.7‰ for δ33S, δ34S and δ36S, respectively. To achieve a higher lateral resolution of ≤2 × 2 μm2, the Cs+ beam was reduced to 7–10 pA with a diameter of ∼200 nm; 32S was measured with the FC and the other signals were measured with the EMs. The external reproducibility (1 SD) was better than 0.5‰ for both δ33S and δ34S and was 3‰ for δ36S. To achieve the highest lateral resolution for the analysis of submicron-sized sulfides, a ∼0.7 pA Cs+ beam of ∼100 nm diameter was used, scanning over areas of 0.5 × 0.5 μm2, and all 32S, 33S and 34S were counted with the EMs. The external reproducibility (1 SD) was better than 1.5‰ for both δ33S and δ34S. These three modes have important applications in the isotope analysis of micron-sized sulfur samples, such as pyrite framboids and areas of complex zoning in sulfide minerals.

Estimating compositions of natural ringwoodite in the heavily shocked Grove Mountains 052049 meteorite from Raman spectra

Abstract A combined Raman spectroscopy and electron probe microanalysis study of the heavily shocked Grove Mountains (GRV) 052049 meteorite revealed the largest chemical fractionation of natural ringwoodite, and composition-dependent variation of the intensities and/or wavenumbers of Raman bands. With Fa content [atomic ratio of Fe/(Fe+Mg)] of ringwoodite varying from 27.8 to 81.6 mol%, the peak position of the single band around 290 cm-1 (SB1), which relates to the SiO4 translation mode, shifts from 296.0 to 284.6 cm-1, and one of the doublets around 790 cm-1 (DB1), which relates to the symmetric stretching of SiO4, shifts from 796.3 to 782.7 cm-1. In addition, the relative intensities of SB1 and the other band of the doublet around 840 cm-1 (DB2), which relates to asymmetric stretching of SiO4, increases with Fa content. Based on the paired Raman-EPMA data, single-peak and two-peak calibrations were established, which can be used to derive Fa contents of ringwoodite from the Raman spectra. The accuracy of Raman-derived Fa content of ringwoodite is better than ±5 mol%. The correlation of SB1 intensity with the Fa content of ringwoodite suggests that the vibration of SB1 is enhanced with the substitution of Mg2+ by Fe2+. The correlation between Raman spectra and the chemical composition of ringwoodite have potential applications in on-line measurement of high-pressure experiments and in situ mineralogical determination in future planetary explorations.

Stardust Investigation into the CR Chondrite Grove Mountain 021710

We report the presolar grain inventory of the CR chondrite Grove Mountain 021710. A total of 35 C-anomalous grains (∼236 ppm) and 112 O-anomalous grains (∼189 ppm) were identified in situ using NanoSIMS ion imaging. Of 35 C-anomalous grains, 28 were determined to be SiC grains by Auger spectroscopy. Seven of the SiC grains were subsequently measured for N and Si isotopes, allowing classification as one nova grain, one Y grain, one Z grain, and four mainstream grains. Eighty-nine out of 112 O-anomalous grains belong to Group 1, indicating origins in low-to-intermediate-mass red giant and asymptotic giant branch stars. Twenty-one are Group 4 grains and have origins in supernovae. Auger spectroscopic elemental measurements of 35 O-anomalous grains show that 33 of them are ferromagnesian silicates. They have higher Mg/(Mg+Fe) ratios than those reported in other meteorites, suggesting a lower degree of alteration in the nebula and/or asteroid parent bodies. Only two oxide grains were identified, with stoichiometric compositions of MgAl2O4 and SiO2, respectively. The presolar silicate/oxide ratio of GRV 021710 is comparable with those of the CR3 chondrites (QUE 99177 and MET 00426) and primitive interplanetary dust particles. In order to search for presolar sulfides, the meteorite was also mapped for S isotopes. However, no presolar sulfides were found, suggesting a maximum abundance of 2 ppm. The scarcity of presolar sulfides may be due to their much faster sputtering rate by cosmic rays compared to silicates.

Two unusual Type B refractory inclusions in the Ningqiang Carbonaceous Chondrite: Evidence for relicts, xenoliths and multi-heating

Abstract Two Type B refractory inclusions, consisting mainly of melilite, fassaite and spinel ± anorthite, were found in the anomalous Ningqiang carbonaceous chondrite. The composition of melilite varies from Ak4–15 near the diopside rims to Ak80–90 in the centers of these inclusions. In addition, melilite exhibits intergrowths with fassaite and/or anorthite in the centers of the inclusions. These observations suggest that both inclusions were once molten. The Na2O content of melilite is positively correlated with the Ak content for Ak Beyond crystallization from melts, the Ningqiang Type B refractory inclusions contain possible relict fassaite fragments. These fragments are embedded in gehlenitic melilite and have corroded outlines surrounded by highly TiO2-enriched fringes, as distinguished from the fassaites intergrown with melilite in the centers of the inclusions. In inclusion NQJ331, most grains of anorthite occur as irregular coarse-grained fragments, distinct from those intergrown with melilite. Toward these anorthite fragments, melilite shows a steep decrease in Ak content. We propose that these anorthite fragments are xenoliths and were probably injected into the host while the latter was crystallizing. Palisades occur only in NQJ331, and are probably relicts too. Distinctly low V2O3 concentrations of the spinels from the palisade bodies and the presence of palisade bodies consisting of one or more corroded crystals of fassaite ± anorthite are new lines of the evidence for a relict origin of palisades. The other Type B refractory inclusion, NQJ354, contains a spherule consisting of a grossite core and a spinel mantle enclosing laths of hibonite. The modal abundance and mineral chemistry of the spinel-hibonite spherule are distinctly different from the host inclusion. We propose that the spinel-hibonite spherule crystallized from a SiO2-poor melt at a very high temperature and was injected into the Type B host before the latter was completely solidified. This grossite-bearing spinel-hibonite spherule may be related to the spinel-hibonite spherules in CM2 chondrites.

Grove Mountains (GRV) 99027: A new Martian meteorite

We report the petrography, mineral chemistry and oxygen isotopic composition of GRV 99027, a new Martian meteorite recently collected during the 16th Chinese Antarctic Research Expedition. This meteorite consists of two textural regions. The interstitial region is characterized by the presence of plagioclase and phosphate, and higher FeO contents of olivine and orthopyroxene, in comparison with the poikilitic region. All of the observations are similar to the three known Martian lherzolites. We classify GRV 99027 as the fourth sample of Martian lherzolite.

Biomineralization mediated by anaerobic methane-consuming cell consortia

Anaerobic methanotrophic archaea (ANME) play a significant role in global carbon cycles. These organisms consume more than 90% of ocean-derived methane and influence the landscape of the seafloor by stimulating the formation of carbonates. ANME frequently form cell consortia with sulfate-reducing bacteria (SRB) of the family Deltaproteobacteria. We investigated the mechanistic link between ANME and the natural consortium by examining anaerobic oxidation of methane (AOM) metabolism and the deposition of biogenetic minerals through high-resolution imaging analysis. All of the cell consortia found in a sample of marine sediment were encrusted by a thick siliceous envelope consisting of laminated and cementing substances, whereas carbonate minerals were not found attached to cells. Beside SRB cells, other bacteria (such as Betaproteobacteria) were found to link with the consortia by adhering to the siliceous crusts. Given the properties of siliceous minerals, we hypothesize that ANME cell consortia can interact with other microorganisms and their substrates via their siliceous envelope, and this mechanism of silicon accumulation may serve in clay mineral formation in marine sedimentary environments. A mechanism for biomineralization mediated by AOM consortia was suggested based on the above observations.