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.
This paper focuses on the post-accretion history of CV3 chondrites, through a combination of petrographic and mineralogical characterization, magnetic measurements, spectral (Raman and Infrared) and ...thermo-gravimetric analysis of 31 meteorites (including 7 falls, 21 Antarctic and 3 non-Antarctic finds) spanning a wide metamorphic range.
We classify the 21 Antarctic chondrites and the Bukhara fall into the CVRed, CVOxA, and CVOxB subgroups. We establish quantitative parameters relevant for this sub-classification. In comparison to CVOx, CVRed chondrites are characterized by (i) a lower abundance of matrix, (ii) a higher abundance of metal, (iii) the presence of Ni-poor sulfides. In comparison to CVOxB, CVOxA are characterized by (i) similar matrix abundance, (ii) a higher abundance of metal, (iii) the presence of metal almost exclusively under the form of awaruite, (iv) lower Ni content of sulfides, (v) lower magnetic susceptibility and saturation remanence.
Both CVOx (CVOxA and CVOxB) and CVRed experienced aqueous alteration, and contain oxyhydroxides and phyllosilicates. We show that the abundance of these hydrated secondary minerals observed today in individual CV chondrites decreases with their peak metamorphic temperature. This is interpreted either as partial dehydration of these secondary minerals or limited hydration due to the rapid exhaustion of the water reservoir during parent body thermal metamorphism. Moreover, the lower abundance of oxyhydroxides (that have a lower thermal stability than phyllosilicates and may in large part postdate the peak of thermal metamorphism) in more metamorphosed CV chondrites is interpreted as lower availability of aqueous fluids during retrograde metamorphism in these meteorites.
Lastly, we show that in comparison to CVOxB, CVOxA are systematically (i) more metamorphosed, (ii) less hydrated, (iii) depleted in ferromagnetic minerals, (iv) but enriched in metal in the form of secondary awaruite. CVOxA may be thermally metamorphosed CVOxB. CVRed are significantly different from CVOx (matrix abundances, alteration products, opaque minerals), but span the same wide metamorphic range. This could be indicative of a laterally heterogeneous CV parent body, or suggest the existence of distinct parent bodies for CVOx and CVRed chondrites.
The 205 Ma Rochechouart impact structure (France) is characterized by various impactite formations overlying the Hercynian crystalline basement. New constraints from downhole logging and surface ...electrical resistivity measurements along >100 m long profiles reveal that the top melt‐bearing breccia layer is more conductive and porous than the underlying melt‐poor breccia layer. The stratigraphy within the impactite and the transition with the basement are irregular at small (∼1–10 m) and medium (>100 m) scales, with vertical amplitude up to 40–50 m. At larger scale (>1 km), audio‐magnetotelluric observations are able to map the lateral and vertical extent of fracturing/brecciation in the basement, reaching 200 m below the surface nearby Chassenon, in the northern part of the structure. Our results also unveil that the impactite deposits and the brecciated basement of the Rochechouart impact structure may have been shifted laterally and vertically during the modification stage of the impact event through displacements of megablocks, which may be associated with the collapse of a central uplift.
Plain Language Summary
The geological formations of the Rochechouart impact structure are mapped using geoelectrical measurements. The electrical properties of impacted rocks differ significantly from the non‐impacted rocks, thus allowing the imaging of the geological contrasts. Our geophysical study reveals the complex topography of the transition between the impactite and the crystalline basement formations at the bottom of such medium‐size impact structure. The lateral and vertical extent of brecciation/fracturation is also investigated using this method, unveiling possible megablocks emplacement throughout a general northward tilting of the crater, which challenges the expected structure of the crater.
Key Points
All impactite formations of the Rochechouart impact structure have a clear electrical signature
Large‐scale electrical investigations unveil a rough transition between impactites and unbrecciated basement, implying possible megablocks
Fracturing/brecciation in the Rochechouart basement locally reaches depths larger than 200 m
The geomagnetic field is predominantly dipolar today, and high-fidelity paleomagnetic mean directions from all over the globe strongly support the geocentric axial dipole (GAD) hypothesis for the ...past few million years. However, the bulk of paleointensity data fails to coincide with the axial dipole prediction of a factor-of-2 equator-to-pole increase in mean field strength, leaving the core dynamo process an enigma. Here, we obtain a multidomain-corrected Pliocene–Pleistocene average paleointensity of 21.6 ± 11.0 μT recorded by 27 lava flows from the Galapagos Archipelago near the Equator. Our new result in conjunction with a published comprehensive study of single-domain–behaved paleointensities from Antarctica (33.4 ± 13.9 μT) that also correspond to GAD directions suggests that the overall average paleomagnetic field over the past few million years has indeed been dominantly dipolar in intensity yet only ∼60% of the present-day field strength, with a long-term average virtual axial dipole magnetic moment of the Earth of only 4.9 ± 2.4 × 1022A·m².
The large-scale compositional structures of planets are primarily established during early global differentiation. Advances in analytical geochemistry, the increasing diversity of extraterrestrial ...samples, and new paleomagnetic data are driving major changes in our understanding of the nature and timing of these early melting processes. In particular, paleomagnetic studies of chondritic and small-body achondritic meteorites have revealed a diversity of magnetic field records. New, more sensitive and highly automated paleomagnetic instrumentation and an improved understanding of meteorite magnetic properties and the effects of shock, weathering, and other secondary processes are permitting primary and secondary magnetization components to be distinguished with increasing confidence. New constraints on the post-accretional histories of meteorite parent bodies now suggest that, contrary to early expectations, few if any meteorites have been definitively shown to retain records of early solar and protoplanetary nebula magnetic fields. However, recent studies of pristine samples coupled with new theoretical insights into the possibility of dynamo generation on small bodies indicate that some meteorites retain records of internally generated fields. These results indicate that some planetesimals formed metallic cores and early dynamos within just a few million years of solar system formation.
The analysis of noble gases in meteorites provides constraints on the early solar system and the pre-solar nebula. This requires a better characterization and understanding of the capture, ...production, and release of noble gases in meteorites. The knowledge of transfer properties of noble gases for each individual meteorite could benefit from using radon-222, radioactive daughter of radium-226. The radon-222 emanating power is commonly quantified by the effective radium-226 concentration (ECRa), the product of the bulk radium-226 concentration and of the emanation coefficient E, which represents the probability of one decaying radium-226 to inject one radon-222 into the free porous network. Owing to a non-destructive, high-sensitivity accumulation method based on long photomultiplier counting sessions, we are now able to measure ECRa of meteorite samples, which usually have mass smaller than 15g and ECRa<0.5Bqkg−1. We report here the results obtained from 41 different meteorites, based on 129 measurements on 70 samples using two variants of our method, showing satisfactory repeatability and a detection limit below 10−2Bqkg−1 for a sample mass of 1g. While two meteorites remain below detection level, we obtain for 39 meteorites heterogeneous ECRa values with mean (min–max range) of ca. 0.1 (0.018–1.30)Bqkg−1. Carbonaceous chondrites exhibit the largest ECRa values and eucrites the smallest. Such values are smaller than typical values from most terrestrial rocks, but comparable with those from Archean rocks (mean of ca. 0.18Bqkg−1), an end-member of terrestrial rocks. Using uranium concentration from the literature, E is inferred from ECRa for all the meteorite samples. Values of E for meteorites (mean 40±4%) are higher than E values for Archean rocks and reported values for lunar and Martian soils. Exceptionally large E values likely suggest that the 238U-226Ra pair would not be at equilibrium in most meteorites and that uranium and/or radium are most likely not uniformly distributed. ECRa of meteorites is correlated with E and seems to mainly reflect the gas permeability of the meteorite, which could be one important property, preserved in the meteorite, of its parent body, characterizing its history in space, possibly modified by alteration, shock metamorphism, and eventually weathering on Earth. Larger radon emanation values are associated with larger concentrations of the heaviest noble gases (argon, krypton, xenon), and larger 20Ne/22Ne and 36Ar/38Ar ratios, suggesting Earth’s atmosphere contamination or solar wind implantation, and probably a similar carrier phase such as Q phase. An unclear correlation is observed with 40Ar, which may rule out a purely radiogenic effect on radon emanation. Thus, larger radon emanation suggests a larger capacity of collecting solar and terrestrial gases, which should imply higher loss of gases generated in the meteorite and larger dispersion of Pb/U ratios for age determination. This study provides the first quantification of natural radon-222 loss from meteorites and opens promising perspectives to quantify the relationship between pore space connectivity and the transfer properties for noble gases in meteorites and other extraterrestrial bodies.
Herpes simplex virus 1 (human herpesvirus 1) initially infects epithelial cells of the mucosa and then goes on to infect sensory neurons leading ultimately to a latent infection in trigeminal ganglia ...(TG). UL24 is a core herpesvirus gene that has been identified as a determinant of pathogenesis in several Alphaherpesvirinae, although the underlying mechanisms are unknown. In a mouse model of ocular infection, a UL24-deficient virus exhibited a reduction in viral titres in tear films of 1 log10, whilst titres in TG are often below the level of detection. Moreover, the efficiency of reactivation from latency was also severely reduced. Herein, we investigated how UL24 contributed to acute infection of TG. Our results comparing the impact of UL24 on viral titres in eye tissue versus in tear films did not reveal a general defect in virus release from the cornea. We also found that the impairment of replication seen in mouse primary embryonic neurons with a UL24-deficient virus was not more severe than that observed in an epithelial cell line. Rather, in situ histological analyses revealed that infection with a UL24-deficient virus led to a significant reduction in the number of acutely infected neurons at 3 days post-infection (p.i.). Moreover, there was a significant reduction in the number of neurons positive for viral DNA at 2 days p.i. for the UL24-deficient virus as compared with that observed for WT or a rescue virus. Our results supported a model whereby UL24 functions in the dissemination of acute infection from the cornea to neurons in TG.
Magnetic fabric, paleomagnetic, and petrophysical studies were conducted on rocks in the Tafresh area of the central Urumieh-Dokhtar magmatic arc in Iran. The samples included Late Triassic dark gray ...sandstone, a mafic dyke, diorites, and a felsic dyke in the Zaghar region. Hydrothermal alteration in the Spid intrusion was investigated to understand the effects of alteration on magnetic fabric patterns. The AMS measurements support the theory that the Nayband Formation was constructed under a crustal extension regime. Magnetic susceptibility anisotropy in a microdioritic dyke indicates compression from the NNE-SSW, likely due to tectonic activity. AMS results from diorites in Zaghar suggest intrusions were emplaced in extensional spaces between the Tafresh and Chaghar thrust faults. The Spid intrusion’s magnetite is the primary carrier of magnetic susceptibility, but hydrothermal alteration has partly converted it into hematite, resulting in lower susceptibility and higher porosity in altered diorites. This process leads to a bimodal distribution of magnetic lineation trends. The Spid and Zaghar massifs underwent a northward tilt of about 30 degrees around an east-west axis following the Early Miocene. Post-Eocene rotations in the area are typically within ±20 degrees. This study demonstrates how magnetic properties can provide new insights into the evolution of tectono-magmatic processes and structural controls within a magmatic arc.
Abstract Mutations in UL24 of herpes simplex virus type 1 can lead to a syncytial phenotype. We hypothesized that UL24 affects the sub-cellular distribution of viral glycoproteins involved in fusion. ...In non-immortalized human foreskin fibroblasts (HFFs) we detected viral glycoproteins B (gB), gD, gH and gL present in extended blotches throughout the cytoplasm with limited nuclear membrane staining; however, in HFFs infected with a UL24-deficient virus (UL24X), staining for the viral glycoproteins appeared as long, thin streaks running across the cell. Interestingly, there was a decrease in co-localized staining of gB and gD with F-actin at late times in UL24X-infected HFFs. Treatment with chemical agents that perturbed the actin cytoskeleton hindered the formation of UL24X-induced syncytia in these cells. These data support a model whereby the UL24 syncytial phenotype results from a mislocalization of viral glycoproteins late in infection.
The present study focused on the petrography and geotechnics of aggregates of two sites around the city of Mongo for their use in construction. The study area is located in central Chad, in the Guéra ...province, at the eastern and north-western entrance to the city of Mongo. The area corresponds to a crystalline basement, and granitic massifs are abundant. Two deposits were studied: the Mongo massif, closest to the town of the same name, and the Oyo massif at the eastern exit of Mongo. The petrographic analysis showed that the studied materials are granites, light grey in color, composed of 30% quartz, 15% biotite, 20% feldspar, 30% plagioclase and 5% other minerals. From the geotechnical point of view, the materials of the Mongo site are more resistant to wear compared to those of Oyo which are less resistant. According to the results of micro-Deval and Los Angeles tests, the use of aggregates obtained from the Mongo site granites are usable in base courses for T1–T3 traffic admitting an axle of 8 to 10 tons and in surface dressings, contrary to those of Oyo, which are not favorable in road construction.
PDF
