Here we show that bulk H, C and N elemental and isotopic analyses can be used to classify CM and CR chondrites. These meteorites in both groups form well-defined trends in plots of H content vs. δD ...and C/H vs. δD, and these trends appear to primarily reflect varying degrees of aqueous alteration. The subset of samples with evidence for thermal alteration plot well away from these trends. In CMs, both bulk H and N isotopic compositions, in particular, strongly correlate with petrologic indicators of the degree of alteration and have been used to classify 54 unheated or weakly heated meteorites on a scale of 2–3. However, extrapolation of the trends based on this scale to type 3.0 predicts relatively high water contents, and the schemes cannot be used to classify altered meteorite belonging to other chondrite groups. Here we propose a different classification scheme based on the degree of hydration (wt.% H in water and OH) of a meteorite that can be determined straightforwardly from a meteorite’s bulk H and C contents. Our estimates of the extent of hydration in CMs correlate well with petrologic estimates of the extent of hydration and with the previously determined phyllosilicate abundances. This is not the case for the CRs, which we suggest is due to cryptic alteration of some CRs at low temperatures.
Increasing the production and applications of TiO
2
nanoparticles (NPs) has led to grow concerns about the consequences for the environment. In this study, we investigated the effects of a set of TiO
...2
NPs on the viability of mussel hemocytes and gill cells using neutral red and thiazolyl tetrazolium bromide assays. For this, we compared the cytotoxicity of TiO
2
NPs (0.1-100 mg Ti/L) produced by different techniques: rutile NPs (60 nm) produced by milling and containing disodium laureth sulfosuccinate (DSLS), rutile NPs (10, 40 and 60 nm) produced by wet chemistry and anatase/rutile NPs (∼100 nm) produced by plasma synthesis. The commercially available P25 anatase/rutile NPs (10-20 nm) were also tested. Exposures were performed in parallel with their respective bulk forms and the cytotoxicity of the additive DSLS was also tested. Z potential values in distilled water indicated different stabilities depending on the NP type and all NPs tested formed agglomerates/aggregates in cell culture media. In general, TiO
2
NPs showed a relatively low and dose-dependent toxicity for both cell models with the two assays tested. NPs produced by milling showed the highest effects, probably due to the toxicity of DSLS. Size-dependent toxicity was found for NPs produced by wet chemistry (10 nm > 40 nm and 60 nm). All TiO
2
NPs tested were more toxic than bulk forms excepting for plasma produced ones, which were the least toxic TiO
2
tested. The mixture bulk anatase/rutile TiO
2
was more toxic than bulk rutile TiO
2
. In conclusion, the toxicity of TiO
2
NPs varied with the mode of synthesis, crystalline structure and size of NPs and can also be influenced by the presence of additives in the suspensions.
Triangulated observations of fireballs allow us to determine orbits and fall positions for meteorites. The great majority of basaltic meteorites are derived from the asteroid 4 Vesta. We report on a ...recent fall that has orbital properties and an oxygen isotope composition that suggest a distinct parent body. Although its orbit was almost entirely contained within Earth's orbit, modeling indicates that it originated from the innermost main belt. Because the meteorite parent body would likely be classified as a V-type asteroid, V-type precursors for basaltic meteorites unrelated to Vesta may reside in the inner main belt. This starting location is in agreement with predictions of a planetesimal evolution model that postulates the formation of differentiated asteroids in the terrestrial planet region, with surviving fragments concentrated in the innermost main belt.
— Darwin glass formed about 800,000 years ago in western Tasmania, Australia. Target rocks at Darwin crater are quartzites and slates (Siluro‐Devonian, Eldon Group). Analyses show 2 groups of glass, ...Average group 1 is composed of: SiO2 (85%), Al2O3 (7.3%), TiO2 (0.05%), FeO (2.2%), MgO (0.9%), and K2O (1.8%). Group 2 has lower average SiO2 (81.1%) and higher average Al2O3 (8.2%). Group 2 is enriched in FeO (+1.5%), MgO (+1.3%) and Ni, Co, and Cr. Average Ni (416 ppm), Co (31 ppm), and Cr (162 ppm) in group 2 are beyond the range of sedimentary rocks. Glass and target rocks have concordant REE patterns (La/Lu = 5.9–10; Eu/Eu* = 0.55–0.65) and overlapping trace element abundances. 87Sr/86Sr ratios for the glasses (0.80778–0.81605) fall in the range (0.76481–1.1212) defined by the rock samples. ε‐Nd results range from –13.57 to –15.86. Nd model ages range from 1.2–1.9 Ga (CHUR) and the glasses (1.2–1.5 Ga) fall within the range defined by the target samples. The 87Sr/86Sr versus 87Rb/86Sr regression age (411 ± 42 Ma) and initial ratio (0.725 ± 0.016), and the initial 43Nd/144Nd ratio (0.51153 ± 000011) and regression age (451 ± 140 Ma) indicate that the glasses have an inherited isotopic signal from the target rocks at Darwin crater. Mixing models using target rock compositions successfully model the glass for all elementsexcept FeO, MgO, Ni, Co, and Cr in group 2. Mixing models using terrestrial ultramafic rocks fail to match the glass compositions and these enrichments may be related to the projectile.
Darwin glass is a siliceous impact glass found in a 400 km
2 strewn field near Mt Darwin, western Tasmania, Australia. It has been dated by Ar–Ar methods at 816
±
7 ka. A 1.2 km diameter circular ...depression, named Darwin Crater (42°18.39′S, 145°39.41′E), is the assumed source crater for the glass. Darwin Crater is situated in a remote rain forested valley developed within Siluro–Devonian quartzite and slate (Eldon Group). Earlier geophysical investigations demonstrated that the structure is an almost circular bowl-shaped sediment-filled basin. This paper provides the first detailed description of the geology of Darwin Crater. The centre of the crater has been penetrated by two drill cores, the deeper to a maximum depth of ∼
230 m. The drill cores intersected fine-grained lacustrine sediments (∼
60 m thick) overlying poorly sorted coarser crater-fill deposits. The pre-lacustrine crater-fill stratigraphy comprises an uppermost polymict breccia (∼
40 m thick) of angular quartz and country rock, which contains very rare (≪
1%) fresh glass fragments (Crater-fill Facies A). Beneath the polymict breccia facies, the drill core intersected monomict sandy breccias of angular quartz (Crater-fill Facies B), and a complicated package of deformed slate clasts (Crater-fill Facies C). Quartz grains in the crater-fill samples contain abundant irregular fractures. In some of the most deformed quartz grains, sub-planar fractures define zones of alternating extinction that superficially resemble twinning. Kinked micas are also present. While the deformation observed in clasts of the crater-fill facies is far greater than in rocks cropping out around the crater, no diagnostic shock indicators, such as planar deformation features (PDF's) in quartz, were observed. If the crater is of impact origin, as seems likely due to the close association with Darwin glass, this is another example of a simple crater where diagnostic shock indicators appear to be absent, preventing confirmation of an impact origin by petrographic analysis of crater-fill samples alone.
•Least-processed meteorites have experienced minimal parent body processing (including thermal metamorphism and aqueous alteration). They are characterized by up to 30 vol.% amorphous matrix ...silicates.•We present near and mid-infrared spectroscopy of 8 least-processed CO meteorites, two CR3 meteorites and one ungrouped least-processed meteorite.•Least processed meteorites from all chemical groups exhibit 1.4-µm and 21-µm features produced by the abundant amorphous silicates present in these meteorites.•This is the first mid-infrared detection of amorphous material in the spectra of least-processed meteorites.•One asteroid, (93) Minerva, appears to have a similar near-infrared spectrum as the least-processed CO meteorites, indicating Minerva has a large abundance of amorphous materials on its surface. Minerva, therefore, preserves these primitive materials and can be considered as the least-processed, most primitive asteroids observed.
Least-processed carbonaceous chondrites (carbonaceous chondrites that have experienced minimal aqueous alteration and thermal metamorphism) are characterized by their predominately amorphous iron-rich silicate interchondrule matrices and chondrule rims. This material is highly susceptible to destruction by the parent body processes of thermal metamorphism or aqueous alteration. The presence of abundant amorphous material in a meteorite indicates that the parent body, or at least a region of the parent body, experienced minimal processing since the time of accretion. The CO chemical group of carbonaceous chondrites has a significant number of these least-processed samples. We present visible/near-infrared and mid-infrared spectra of eight least-processed CO meteorites (petrologic type 3.0–3.1). In the visible/near-infrared, these COs are characterized by a broad weak feature that was first observed by Cloutis et al. (2012) to be at 1.3-µm and attributed to iron-rich amorphous silicate matrix materials. This feature is observed to be centered at 1.4-µm for terrestrially unweathered, least-processed CO meteorites. At mid-infrared wavelengths, a 21-µm feature, consistent with Si–O vibrations of amorphous materials and glasses, is also present. The spectral features of iron-rich amorphous silicate matrix are absent in both the near- and mid-infrared spectra of higher metamorphic grade COs because this material has recrystallized as crystalline olivine. Furthermore, spectra of least-processed primitive meteorites from other chemical groups (CRs, MET 00426 and QUE 99177, and C2-ungrouped Acfer 094), also exhibit a 21-µm feature. Thus, we conclude that the 1.4- and 21-µm features are characteristic of primitive least-processed meteorites from all chemical groups of carbonaceous chondrites. Finally, we present an IRTF + SPeX observation of asteroid (93) Minerva that has spectral similarities in the visible/near-infrared to the least-processed CO carbonaceous chondrites. While Minerva is not the only CO-like asteroid (e.g., Burbine et al., 2001), Minerva is likely the least-processed CO-like asteroid observed to date.
Using position sensitive detector X-ray diffraction (PSD-XRD) we determine a complete modal mineralogy for all phases present in abundances greater than 1
wt% in Vigarano, Efremovka, Mokoia, ...Grosnaja, Kaba and Allende. Reduced CV3 samples are comprised of (vol%): olivine (83–85%); enstatite (6.5–8.1%); anorthite (1.1–1.2%); magnetite (1.4–1.8%); sulphide (2.4–5.1%); Fe, Ni metal (2–2.2%). The oxidized samples are comprised of: olivine (76.3–83.9%); enstatite (4.8–7.8%); anorthite (1.1–1.7%); magnetite (0.3–6.1%); sulphide (2.9–8.1%); Fe, Ni metal (0.2–1.1%); Fe-oxide (0–2.7%) and phyllosilicate (1.9–4.2%). When our modal data is used to calculate a bulk chemistry that is compared to literature data a near 1:1 correlation is observed. PSD-XRD data indicates that olivine compositions may span almost the entire Fe–Mg solid solution series in all CV samples and that these contain a component (4–13%) of fine-grained olivine that is more Fe-rich (>Fa
60) than is typically reported. Modal mineralogy shows that there are mineralogic differences between CV3 samples classified as oxidized and reduced but that these sub-classes are most clearly distinguished by the relative abundance of metal and Ni content of sulphide, rather than abundance of magnetite. The most significant difference in modal mineralogy observed is the relative absence of phyllosilicate in reduced CV that essentially escaped aqueous alteration.
Fayalite, ferrous olivine and magnetite are typically considered secondary alteration products. The abundances of these minerals overlap in oxidized and reduced samples and correlate positively supporting common conditions of formation in a relatively oxidizing environment. The abundances of fayalite, ferrous olivine and magnetite show no relationship to petrographic type and if these abundances were used as a proxy for alteration, Allende would be the least altered CV – contrary to all previous data. The implication is that thermal metamorphism on the parent body was de-coupled from formation of Fe-rich secondary minerals. Low temperature fluid-assisted metamorphism can also not easily explain the origin of fayalite, ferrous olivine and magnetite, since the reduced CVs appear to be largely unaffected by this process. Parent body models require an anhydrous low-temperature mechanism of secondary alteration. The alternative is that these phases formed prior to accretion of the final CV parent body.
Increasing the production and applications of TiOsub 2 nanoparticles (NPs) has led to grow concerns about the consequences for the environment. In this study, we investigated the effects of a set of ...TiO2 NPs on the viability of mussel hemocytes and gill cells using neutral red and thiazolyl tetrazolium bromide assays. For this, we compared the cytotoxicity of TiOsub 2 NPs produced by different techniques: rutile NPs produced by milling and containing disodium laureth sulfosuccinate (DSLS), rutile NPs produced by wet chemistry and anatase/rutile NPs produced by plasma synthesis. The commercially available P25 anatase/rutile NPs were also tested. Exposures were performed in parallel with their respective bulk forms and the cytotoxicity of the additive DSLS was also tested. Inconclusion, the toxicity of TiOsub 2 NPs varied with the mode of synthesis, crystalline structure and size of NPs and can also be influenced by the presence of additives in the suspensions.
Although a crater is not yet identified, the Australasian tektite strewn field provides evidence that a major impact cratering event took place in the Southeast Asian region at ∼0.8 Ma, just prior to ...the Brunhes/Matuyama geomagnetic polarity reversal. Paleomagnetic evidence including reversed polarity in mud lens closely associated with in situ tektites suggests that tektite-bearing flood deposits near Ban Ta Chang and Chum Phuang in northeast Thailand are penecontemporaneous with the impact event. The deposits include abundant organic debris, including whole tree trunks and mammal bones, that preserved due to reducing conditions, which are also responsible for the presence of abundant iron sulphides. Sedimentological observations suggest a series of major flood events that are out of character with the modern meandering river system to which they are related. The deposits are consistent with the effects of regional deforestation, increased run off and erosion, and other environmental disruptions expected in the aftermath of a major impact event.
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