Petrologic Type Research Articles

Positive correlation between shock stage and petrologic type in ordinary chondrites: Implications for the internal structures and thermal histories of ordinary‐chondrite parent asteroids

Positive correlation between shock stage and petrologic type in ordinary chondrites: Implications for the internal structures and thermal histories of ordinary‐chondrite parent asteroids

Hf–W isotope systematics of bulk chondrites: Implications for early Solar System evolution

The short-lived 182Hf–182W system is widely used for constraining the chronology of the early Solar System, including the timing of the formation, thermal evolution, and differentiation of planetary bodies. Utilizing the full potential of the Hf–W system requires knowledge of the Hf/W ratio and W isotopic composition of primitive chondritic material. However, metal-silicate heterogeneity among chondritic samples can complicate accurately determining the Hf–W systematics of bulk chondrite parent bodies. Moreover, interpreting Hf–W data for chondrites may be complicated by potential nucleosynthetic W isotope anomalies. To this end, we report Hf/W ratios and W isotope compositions for bulk ordinary and enstatite chondrites, as well as the first such data for Rumuruti chondrites. We find that ordinary and Rumuruti chondrites show no resolvable nucleosynthetic anomalies, whereas resolved ε183W (i.e., 0.01 % deviation in 183W/184W from terrestrial standard) excesses in individual enstatite chondrites suggest the presence of nucleosynthetic W isotope anomalies in bulk meteorite samples originating in the inner Solar System. These anomalies necessitate corrections when accurately quantifying radiogenic 182W variations. Furthermore, several ordinary chondrites deviate in Hf/W ratios and W composition from the parent body compositions previously obtained from internal 182Hf–182W isochrons, indicating variations in the abundance of metal across different chondrite samples. Similarly, the Hf–W systematics of some enstatite chondrites also deviate from the parent body values, which can be attributed to the heterogeneous distribution of Hf carrier phases. The new observations highlight the challenges in obtaining Hf-W data that are representative of the chondrite parent bodies from individual chondrites, especially from metal-rich samples. By contrast, Rumuruti chondrites of variable petrologic types exhibit uniform Hf/W and 182W/184W ratios, suggesting that these samples are representative of their parent body. Whereas their Hf/W ratio is similar to that of carbonaceous chondrites, their W isotope composition is less radiogenic. This indicates that the Rumuruti precursor reservoir most likely had a significantly lower Hf/W ratio than the ratio measured in Rumuruti chondrites today. These findings underscore the importance of understanding the likely variations in Hf-W isotope systematics of iron meteorite parent bodies for accurately determining the timing of core formation.

Assessment of Borač-Kotlenik magmatic massif rock mass technical properties as potential source for optimal development of regional road infrastructure based on local stone materials

The Borač-Kotlenik magmatic massif in central Serbia is mainly made up of effusive and pyroclastic rocks, formed in three main phases of volcanic activity: 1. dacite and andesite, 2. quartz-latite and dacite, and 3. basaltoid rocks. Rock mass samples from this magmatic massif have been examined and mined in numerous localities during the XX century for purposes of building and reconstruction works of local and regional road networks. The examination process continues today for purposes of ‘Morava corridor’ highway building and its demand for the local stone material of the specified quality. The results of rock mass technical properties' tests have shown that its quality for road building purposes depends significantly on petrologic type, soundness, and hydrothermal alteration type. Oxidation alteration types can cause a significant decrease in compressive strength, an increase in porosity and water absorption, especially as oxidation chemical processes cause increased susceptibility to weathering, thus making the rock mass unusable in road construction profile layers above the embankment. Testing results demonstrate that effusive volcanic rocks of the Borač-Kotlenik magmatic massif generally can be used in the road building process. For this purpose, it is necessary to select the conformable rock mass zones at each locality, where hydrothermal alteration and weathering products are absent in order to obtain the best available stone material of volcanic origin.

Petrology, Mineralogy, and Stable Isotopic Composition of NWA 13943 (CK5) Carbonaceous Chondrite

Karoonda-like (CK) carbonaceous chondrites are highly oxidized meteorites, with metal-to-magnetite ratio close to zero. Unlike other carbonaceous chondrites (petrologic type: 1–3), most CK chondrites have undergone thermal metamorphism (550–1270 K) on their parent body with a petrologic type 4 or above. Lines of evidence suggest a genetic relationship between CK chondrites and Vigarano-like (CV) carbonaceous chondrites, which are predominantly type 3. However, observable petrographic distinctions persist between the two groups. Thus, a thorough reevaluation of their geochemical discrepancies is critical to test the CK-CV single parent body hypothesis. Northwest Africa (NWA) 13943, a newly discovered meteorite subjected to intense modification, was classified using scanning electron microscopy and electron microprobe techniques. High-precision measurements of the mass-independent chromium isotope compositions (ε53Cr and ε54Cr) and the mass-dependent oxygen isotope compositions (δ17O and δ18O) of NWA 13943 were reported for the first time. Integrating petrological, mineralogical, oxygen, and chromium isotopic data, it is legitimated to infer that CK and CV chondrites may originate from two proximal but distinct isotopic reservoirs within the protoplanetary disk.

The Aguas Zarcas carbonaceous chondrite meteorite: Brecciation and aqueous alteration on the parent body

AbstractCM chondrites are samples from primitive water‐rich asteroids that formed early in the solar system; many record evidence for silicate rock–liquid water interaction. Many CM chondrites also exhibit well‐developed fine‐grained rims (FGRs) that surround major components, including chondrules and refractory inclusions. Previous studies have shown that Aguas Zarcas, a CM2 chondrite fall recovered in 2019, is a breccia consisting of several lithologies. Here, we present a study of Aguas Zarcas using optical microscopy, scanning electron microscopy, and electron probe microanalysis, focusing on brecciation and aqueous alteration on the parent body. We observed two lithologies within our sample, separated by a distinct textural and chemical boundary. The first lithology has a higher chondrule abundance (“chondrule‐rich”) and significantly larger FGRs compared to the second lithology (“chondrule‐poor”), even for similarly sized chondrules. We observed clear compositional differences between the two lithologies and more multilayered FGRs in the chondrule‐rich lithology. We determined that the chondrule‐rich lithology is less altered (petrologic type 2.7–2.8) and displays larger FGRs to chondrule ratios compared to the more altered chondrule‐poor lithology (petrologic type 2.5–2.6). These observations are contrary to previous models that predict aqueous alteration as a cause of FGR formation in the parent body. Our observed differences in Mg and Fe distribution in the lithology matrices alongside variable FGR thickness suggest distinct formation environments. We propose that the Aguas Zarcas parent body was subjected to several minor and major brecciation events that mixed different materials with variable degrees of aqueous alteration together, in agreement with previous studies.

3D porosity, flow, and transport characteristics of two L chondrites reveal wet accretion-related cosmic web-like porosity

Porosity, with its structure-dependent flow properties (permeability and tortuosity) and transport properties (thermal conductivity and thermal diffusivity), is closely related to the accretion, thermal metamorphism, and associated hydrothermal alteration of ordinary chondrite (OC) parent bodies. Using synchrotron radiation microtomography (SRμCT), we reveal the varying porosity structures in two L chondrite falls of low (Mezö-Madaras L3.7) and high (Bath Furnace L6) petrologic types and quantify porosity properties, such as shape and connectivity, and related effective permeability and tortuosity factor. Although the two specimens demonstrate similar effective permeabilities, they exhibit significantly different tortuosity factors and textures of porosity, which include notable differences in void throat diameters, complexity and density of the interconnected void network, heterogeneity in void distribution, and the extent of primary and secondary porosity. The complex relationships among porosity, permeability, tortuosity, and thermal conductivity can be explained by the varying void arrangements related to varying grain sizes among the petrologic types of OCs, which in turn reflect their varying evolutionary paths.Electron microprobe and attached energy-dispersive X-ray spectrometer reveal signs of hydrothermal alteration in both petrologic types. High-energy SRμCT imaging (0.65 μm voxel size) reveals the presence of a new microporosity substructure resembling a microscopic cosmic web, which may be linked to fluid-assisted metamorphism and hydrothermal alteration during wet accretion of the parent body. Furthermore, the proportion of this continuous porosity may be related to the temperatures associated with different petrologic types, and the wet accretion model may resolve the lack of correlation between petrologic types and porosity of OCs. Finally, the uncovered cosmic web-like microporosity structure may explain the observed concurrent high thermal conductivity, low permeability, and high porosity of the high-petrologic-type OCs.

Oxygen Isotopic Variations in the Calcium, Aluminum-rich Inclusion–forming Region Recorded by a Single Refractory Inclusion from the CO3.1 Carbonaceous Chondrite Dar al Gani 083

Calcium, aluminum-rich inclusions (CAIs) are the oldest solids dated that formed in the solar system. Most CAIs in unmetamorphosed chondritic meteorites (chondrites; petrologic type ≤3.0) have uniform solar-like 16O-rich compositions (Δ17O ∼ −24‰) and a high initial 26Al/27Al ratio [(26Al/27Al)0] of ∼(4–5) × 10−5, consistent with their origin in a gas of approximately solar composition during a brief (<0.3 Ma) epoch at the earliest stage of our solar system. The nature of O-isotope heterogeneity in CAIs (Δ17O range from ∼−24 up to ∼+5‰) from weakly metamorphosed chondrites (petrologic type >3.0) remains an open issue. This heterogeneity could have recorded fluctuations of O-isotope composition of nebular gas in the CAI-forming region and/or postcrystallization O-isotope exchange of CAI minerals with aqueous fluids on the chondrite parent asteroids. To obtain insights into possible processes resulting in this heterogeneity, we investigated the mineralogy, rare-earth element abundances, and O- and Mg-isotope compositions of a CAI from the CO3.1 chondrite Dar al Gani 083. This concentrically zoned inclusion has a Zn-hercynite core surrounded by layers of (from core to edge) grossite, spinel, melilite, and Al-diopside. The various phases have heterogeneous Δ17O (from core to edge): −2.2 ± 0.6‰, −0.9 ± 2.1‰, −13.7 ± 2.1‰, −2.6 ± 2.3‰, and −22.6 ± 2.1‰, respectively. Magnesium-isotope compositions of grossite, spinel, melilite, and Al-diopside define an undisturbed internal Al–Mg isochron with (26Al/27Al)0 of (2.60 ± 0.29) × 10−6. We conclude that the variations in Δ17O of spinel and diopside recorded fluctuations in O-isotope composition of nebular gas in the CAI-forming region prior to injection and/or homogenization of 26Al at the canonical level. The 16O depletion of grossite and melilite resulted from O-isotope exchange with asteroidal fluid, which did not disturb Al–Mg isotope systematics of the CAI primary minerals.

Space weathering, grain size, and metamorphic heating effects on ordinary chondrite spectral reflectance parameters

AbstractThe exposure to irradiation from high‐energy particles alters the reflectance properties of asteroid surfaces and is referred to as space weathering. This process leads to an increase in spectral slope in visible and near‐infrared wavelengths. However, changes in the regolith particle size, which can vary dramatically among the asteroid population, are known to influence the spectral properties of meteorites and asteroids. In this context, we investigate the changes in spectral slope and absorption band depths of fresh and irradiated ordinary chondrite meteorites to quantitatively compare the effects of space weathering and grain size variations. To do so, we develop and employ the Spectral Analysis for Asteroid Reflectance Investigation routine that calculates the band parameters of reflectance spectra. We then formulate a parameter called the Space Weathering Index (SWI) that is designed to encapsulate spectral changes due to space weathering. We find that the SWI is strongly dependent on the spectral slope which complicates the interpretation of asteroid spectra in the context of grain size variations and space weathering. We also show that a second parameter, the Band Depth Index, is indicative of petrologic type. Finally, we use a linear discriminant analysis to classify asteroid reflectance spectra into H, L, LL, and unequilibrated ordinary chondrites.

Forsteritic olivine in EH (enstatite) chondrite meteorites: A record of nebular, metamorphic, and crystal‐lattice diffusion effects

AbstractThe occurrence of forsteritic olivine in EH enstatite chondrites is indicative of bulk disequilibrium. In MgO‐rich magmatic systems, forsterite can either crystallize as a liquidus phase or be produced during peritectic melting of enstatite. Because diffusion of divalent cations through forsterite is relatively rapid, it records peak melting (i.e., chondrule‐forming events) and is also sensitive to subsequent metamorphism in the EH chondrite parent body. Here, we report the major and minor element geochemistry of olivine in EH chondrites across petrologic types 3 and 4. In all cases, olivine meets the technical definition of forsterite (&gt;90 mole% Mg2SiO4). For unequilibrated EH chondrites, minor elements identify CaO‐Al2O3‐TiO2‐rich (refractory forsterite), MnO‐rich (“LIME” forsterite), and FeO‐bearing (forsteritic olivine) endmember components, the latter with Cr2O3‐rich and Cr2O3‐poor varieties. At higher petrologic type, minor element concentrations become restricted and compositions approach pure forsterite, while grain sizes reduce strongly with peak metamorphic temperatures. These changes reflect diffusive equilibration with enstatitic groundmass and dissolution reaction with free silica. The global geochemical distribution of forsteritic olivine in EH chondrites is, perhaps unexpectedly, more similar to those in low‐FeO type I chondrules and associated objects in carbonaceous chondrites (CCs), rather than equivalent objects in ordinary (H, L, LL), low‐FeO (or HH), or Kakangari (K) chondrites. Among achondrites, there is similarity between pure forsterite in aubrites and EH4 chondrites arising due to subsolidus equilibration in both settings, while Cr2O3‐poor forsteritic olivine in EH3 and CCs is similar to magnesian xenocrystic olivine in angrites. This might reflect CaO‐rich and SiO2‐poor magmatic sources across multiple early solar system reservoirs.

The water content of CM carbonaceous chondrite falls and finds, and their susceptibility to terrestrial contamination

AbstractCM carbonaceous chondrites can be used to constrain the abundance and H isotopic composition of water and OH in C‐complex asteroids. Previous measurements of the water/OH content of the CMs are at the higher end of the compositional range of asteroids as determined by remote sensing. One possible explanation is that the indigenous water/OH content of meteorites has been overestimated due to contamination during their time on Earth. Here we have sought to better understand the magnitude and rate of terrestrial contamination through quantifying the concentration and H isotopic composition of telluric and indigenous water in CM falls by stepwise pyrolysis. These measurements have been integrated with published pyrolysis data from CM falls and finds. Once exposed to Earth's atmosphere CM falls are contaminated rapidly, with some acquiring weight percent concentrations of water within days. The amount of water added does not progressively increase with time because CM falls have a similar range of adsorbed water contents to finds. Instead, the petrologic types of CMs strongly influence the amount of terrestrial water that they can acquire. This relationship is probably controlled by mineralogical and/or petrophysical properties of the meteorites that affect their hygroscopicity. Irrespective of the quantity of water that a sample adsorbs or its terrestrial age, there is minimal exchange of H in indigenous phyllosilicates with the terrestrial environment. The falls and finds discussed here contain 1.9–10.5 wt% indigenous water (average 7.0 wt%) that is consistent with recent measurements of C‐complex asteroids including Bennu.

Nature and timing of a significant reduction event on the L‐chondrite parent asteroid

AbstractAbout 17% of L6 chondrites (15/87) show significant reduction features in BSE images in thin section. Because some thin sections of these meteorites do not show reduction features, this percentage is a lower limit. Reduction features include: (1) 4–5‐μm‐thick BSE‐dark reduction rims on olivine and orthopyroxene grains and along fracture boundaries in these grains, (2) 4–12‐μm‐thick dark bands (probably poorly crystalline pyrrhotite) at the margins and along fractures in troilite grains, and (3) 2–5‐μm‐thick dark rinds of kamacite around some taenite grains. Only one of 70 L‐group chondrites (1.4%) of lower petrologic type exhibits minor reduction. The L6 chondrites showing major reduction have 40Ar/39Ar plateau ages ranging from 156 ± 1 Ma for Guangnan to 4543 ± 3 Ma for Thamaniyat Ajras. Reduction occurred after silicate, sulfide, and metal grains had attained their present sizes during parent‐body thermal metamorphism (and had been fractured by parent‐body collisions). The precise plateau age of Thamaniyat Ajras probably marks the timing of the L6 reduction event. It seems likely the reductant was a low‐viscosity fluid, plausibly CO, derived from oxidation of poorly graphitized and amorphous carbon within fine‐grained matrix. Water‐ice that had accreted to the L‐chondrite asteroid was heated and mobilized during metamorphism, causing oxidation. After peak metamorphism, ~75% of the water had been used up or lost; the remaining water facilitated continuing graphite oxidation so that, after this point, overall reduction effects exceeded those of oxidation. L chondrites of lower petrologic type were less affected by reduction due to their lower metamorphic temperatures.

Physical properties and average atomic numbers of chondrules using computed tomography

Micro-computed tomography is a fast and essentially non-destructive technique for studying 3D properties of solid objects. This study explores the use of a micro-CT technique to determine the physical properties and average atomic numbers of 44 chondrules from unequilibrated (petrologic type 3.00 to 3.6) ordinary, carbonaceous, and enstatite chondrites. Many chondrules deviate from a spherical geometry, implying that they were affected by strain during cooling and prior to complete solidification. The porosity of the studied chondrules ranges from 0.04 vol% to 5.3 vol%. Chondrules from carbonaceous chondrites show the highest porosity and the largest voids. The high porosity could be caused by the presence of oxidized precursors in the chondrule melt that escaped as a gas during high temperature processing and crystallization of the melt. In some chondrules, pores are associated with opaque phases, suggesting their formation either during solidification of metal phases and/or during aqueous alteration. The average atomic numbers of chondrules range from 35 ± 4 to 22 ± 2, independently of porosity and opaque content and is likely controlled by the variation of Mg/Fe in chondrule silicates. The absence of a consistent variation between the degree of deformation, chondrule diameter, and porosity among the studied chondrules from different groups, suggests that the processes responsible for the different physical properties of the chondrules are decoupled from each other and are likely universal to all chondrules.

Saint‐Pierre‐le‐Viger (L5‐6) from asteroid 2023 CX1recovered in the Normandy, France—220 years after the historic fall of L'Aigle (L6 breccia) in the neighborhood

AbstractOn February 13, 2023, a huge fireball was visible over Western Europe (fireball event 2023 CX1). After the possible strewn field was calculated, the first of several recovered samples, with a mass of about 100 g, was discovered just 2 days after the fireball event on the ground of the village of Saint‐Pierre‐le‐Viger. Meanwhile, more than 60 samples with a total mass of more than 1 kg were recovered and a piece of one of these is studied here. The fall occurred 220 years after the historic meteorite fall of L'Aigle on April 26, 1803, &lt;120 km south. L'Aigle is the closest meteorite fall to Saint‐Pierre‐le‐Viger and belongs to the same chondrite group. Both meteorites are breccias containing only clasts of high metamorphic degree (type 5 and type 6). Since only 20% of the L chondrites are breccias this coincidence is remarkable. As just mentioned, both samples studied from these rocks in this work are ordinary chondrite breccias and consist of equilibrated and recrystallized lithologies of petrologic type 6. The brecciated texture in L'Aigle, resulting in a remarkable light–dark structure, is more pronounced than the brecciated features in Saint‐Pierre‐le‐Viger, from which also type 5 fragments have been reported. The compositions of low‐Ca pyroxene and olivine grains in Saint‐Pierre‐le‐Viger (Fs21.2and Fa23.4, respectively) clearly require an L‐group classification. L'Aigle was classified as an L6 breccia in the past, and this has now been confirmed by new data on low‐Ca pyroxene and olivine (Fs20.7and Fa23.8, respectively). Saint‐Pierre‐le‐Viger contains local thin shock veins, and both meteorites are moderately shocked. Most olivines in the studied samples have planar fractures, but the estimated abundance of mosaicized olivines of 30%–40% among the large grains require a S4 shock classification. Oxygen isotope and bulk chemical data of Saint‐Pierre‐le‐Viger certainly support the L chondrite classification. Bulk spectral data of Saint‐Pierre‐le‐Viger are dominated by silicate minerals, that is, Fe‐bearing low‐Ca pyroxene, olivine, and plagioclase. Isotopic, chemical, and spectral data of the L'Aigle meteorite are shown for comparison and are very similar, providing additional circumstantial evidence of Saint‐Pierre‐le‐Viger's L chondritic nature.

Investigation of the porosity of L/LL4 ordinary chondrite Bjurböle using synchrotron radiation microtomography and scanning electron microscopy: Implications for parent body evolution

Porosity is an essential property of chondritic meteorites and is closely related to the genesis, thermal evolution, metamorphism, and thermal properties of the meteorite parent bodies. We study porosity, its texture, and shapes at sub-micron resolution in 3D and 2D within a 0.35 cm3 sample of the L/LL4 ordinary chondrite (OC) Bjurböle using two techniques, synchrotron radiation microtomography (SRμCT) and scanning electron microscopy (SEM). We employ automated segmentation tools that can be applied to both SRμCT and SEM data. Successful segmentation results can be achieved by combining visual qualitative examination and machine learning algorithms.We report novel measurement results of three-dimensional porosity properties of Bjurböle, such as aspect ratio and connectivity of void spaces, and compare the results of 2D and 3D porosity analysis. The Bjurböle sample in this study is a complex, highly porous, and friable medium and the dominant type of porosity is intergranular, continuous porosity, which contains almost all porosity volume. The shapes of the void volumes have an important effect on the connectivity of the porosity and thermal transport properties. Positive correlations between void diameter and aspect ratio as well as void volume and connectivity are present in Bjurböle, which indicate that smaller voids have lower aspect ratios and lower connectivity. In Bjurböle, small, near-spherical voids with few connections have the highest relative frequency, whereas larger void spaces with higher aspect ratios and connectivity are significantly fewer. Completely isolated pores, i.e., voids surrounded by solid material, also have a high relative frequency, and they exist within the chondrules and the matrix. However, the volume percentage of these pores is negligible compared to that of the continuous porosity.Our results support the previously measured high porosities of Bjurböle. The volume percentage of intergranular void spaces, in particular in the matrix, and the measured high porosities are not in line with the results of thermal evolution and sintering models of chondritic parent bodies regarding petrologic type 4, which implies that Bjurböle originates from a parent body with an initial onion shell structure that fragmented during or after its metamorphic peak and quickly reaccreted into a rubble pile.

The bulk mineralogy, elemental composition, and water content of the Winchcombe CM chondrite fall

AbstractOn the microscale, the Winchcombe CM carbonaceous chondrite contains a number of lithological units with a variety of degrees of aqueous alteration. However, an understanding of the average hydration state is useful when comparing to other meteorites and remote observations of airless bodies. We report correlated bulk analyses on multiple subsamples of the Winchcombe meteorite, determining an average phyllosilicate fraction petrologic type of 1.2 and an average water content of 11.9 wt%. We show the elemental composition and distribution of iron and iron oxidation state are consistent with measurements from other CM chondrites; however, Winchcombe shows a low Hg concentration of 58.1 ± 0.5 ng g−1. We demonstrate that infrared reflectance spectra of Winchcombe are consistent with its bulk modal mineralogy, and comparable to other CM chondrites with similar average petrologic types. Finally, we also evaluate whether spectral parameters can estimate H/Si ratios and water abundances, finding generally spectral parameters underestimate water abundance compared to measured values.

Quantitative evolved gas analysis: Winchcombe in comparison with other CM2 meteorites

AbstractTwo bulk Winchcombe along with six other CM2 meteorite samples were subjected to quantitative evolved gas analysis. The observed release patterns for almost all volatile species demonstrate close similarity for all the samples and especially between those for Winchcombe. This can be considered as a fingerprint for this petrological type of meteorites. We identified several gases including H2, H2O, O2, CO, CO2, and SO2 released in different temperature ranges. The sources and mechanisms of their release were also established. Some of the gases, H2, CO, and CO2, are released as a result of oxidation of macromolecular organic material from oxygen derived from oxygen‐bearing minerals (a part of CO2 is also released as a result of decomposition of carbonates). The others, O2 and H2O, are associated with the phase transformation/decomposition of phyllosilicates and (oxy)hydrates, while a high‐temperature release of SO2 is associated mostly with the decomposition of sulfides and in few cases also with sulfates. A low‐temperature release of SO2 is due to evaporation and oxidation of elemental sulfur from the meteoritic matrix and organic material. The total concentrations of H (mostly represented by H2O), C, and S, calculated according to calibration of the quadrupole mass spectrometer with reference gases and decomposition of solid samples (CaSO4·2H2O and NaHCO3) are in reasonable agreement with those determined by independent methods. Variations in the ratio of the carbon amounts released as CO2 and CO (/CCO) between the samples could be an indicator of their terrestrial weathering.

The Santa Filomena meteorite shower: Trajectory, classification, and opaque phases as indicators of metamorphic conditions

AbstractOn August 19, 2020, at 13:18—UTC, a meteor event ended as a meteorite shower in Santa Filomena, a city in the Pernambuco State, northeast Brazil. The heliocentric orbital parameters resulting from images by cameras of the weather broadcasting system were semimajor axis a = 2.1 ± 0.1 au, eccentricity e = 0.55 ± 0.03, and inclination i = 0.15o ± 0.05. The data identified the body as an Apollo object, an Earth‐crossing object with a pericenter interior to the Earth's orbit. The chemical, mineralogical, and petrological evaluations, as well as the physical analysis, followed several traditional techniques. The meteorite was identified as a H5‐6 S4 W0 ordinary chondrite genomict breccia. The large amount of metal in the meteorite made a metallographic evaluation based on the opaque phases possible. The monocrystalline kamacite crystals suggest a higher petrological type and the distorted Neumann lines imply at least two different shock events. The absence of the plessite phase shows that the meteorite did not reach the highest shock levels S5 and S6. The well‐defined polycrystalline taenite is indicative of petrologic types 4 and 5 due to the conserved internal tetrataenite rim at the boundaries. The presence of polycrystalline taenites and the characteristics of the Agrell Effect suggest that the Santa Filomena meteorite did not reheat above 700°C. The absence of martensite confirms reheating temperatures &lt;800°C and a slow cooling rate. The Ni contents and sizes of the zoned taenite particles indicate a slow cooling rate ranging from 1 to 10 K Myr−1.

Geological Characteristics and Paleoenvironmental Evolution of Fine-Grained Sediments in the Third Member of the Xujiahe Formation in the Western Sichuan Depression, SW China

This study investigated, in detail, the characteristics of the Late Triassic fine-grained sediments in the third member of the Xujiahe Formation (Xu-3 Member), in the Western Sichuan Depression, and the paleoenvironmental evolution during their deposition through petrological interpretation, mineralogical composition characterization, and element geochemical analysis. According to the mineralogical composition, the Xu-3 Member can be divided into two petrological types, namely clayey fine-grained felsic sedimentary rocks and lime fine-grained felsic sedimentary rocks. The main mineral components are siliceous, clay, and carbonate minerals. Through the cluster analysis of major elements, all samples could be divided into two types with different major elemental characteristics. Trace elements exhibited distinct Sr depletion, relative enrichment of large ion lithophile elements, and high field strength elements. Two REE enrichment patterns were observed, which could be attributed to differences in the provenance area and tectonic background. The paleoclimate of the sedimentary area was warm and humid, but it was hotter and drier in the southern and central parts of the depression. The change trend of paleo-productivity was consistent with the paleoclimate. The waters in the sedimentary environment were mainly brackish water to saline water, with fresh water in the southern part of the depression. The paleo-redox conditions of the waters were mainly sub-oxidation to sub-reduction, but the southern part of the depression was more oxidative. The provenance area experienced a moderate degree of chemical weathering under a warm and humid paleoclimate, same as the depositional area. However, the depositional environments differed between the northern and south-central parts of the depression.

Parent body histories recorded in Rumuruti chondrite sulfides: Implications for the onset of oxidized, sulfur‐rich core formation

AbstractModels of planetary core formation beginning with melting of Fe,Ni metal and troilite are not readily applicable to oxidized and sulfur‐rich chondrites containing only trace quantities of metal. Cores formed in these bodies must be dominated by sulfides. Siderophile trace elements used to model metallic core formation could be used to model oxidized, sulfide‐dominated core formation and identify related meteorites if their trace element systematics can be quantified. Insufficient information exists regarding the behavior of these core‐forming elements among sulfides during metamorphism prior to anatexis. Major, minor, and trace element concentrations of sulfides are reported in this study for petrologic type 3–6 R chondrite materials. Sulfide‐dominated core‐forming components in such oxidized chondrites (ƒO2 ≥ iron‐wüstite) follow metamorphic evolutionary pathways that are distinct from reduced, metal‐bearing counterparts. Most siderophile trace elements partition into pentlandite at approximately 10× chondritic abundances, but Pt, W, Mo, Ga, and Ge are depleted by 1–2 orders of magnitude relative to siderophile elements with similar volatilities. The distribution of siderophile elements is further altered during hydrothermal alteration as pyrrhotite oxidizes to form magnetite. Oxidized, sulfide‐dominated core formation differs from metallic core formation models both physically and geochemically. Incongruent melting of pentlandite at 865°C generates melts capable of migrating along solid silicate grains, which can segregate to form a Ni,S‐rich core at lower temperatures compared to reduced differentiated parent bodies and with distinct siderophile interelement proportions.

Northwest Africa 8418: The first CV4 chondrite

AbstractNorthwest Africa (NWA) 8418 is an unusual chondrite whose properties do not exactly match those of any other known chondrite. It has similarities to the CV (Vigarano group), CK (Karoonda group), and CL (Loongana group) chondrites, but its abundance of large calcium‐aluminum‐rich inclusions (CAIs) and the low NiO content (&lt;0.2 wt%) of its matrix olivine ally it most closely with the CV group. The absence of grossular, monticellite, wollastonite, and sodalite from the alteration products of the CAIs; the magnesium‐rich nature of the matrix olivines (Fa38) relative to that of the CV3 chondrites (~Fa50); and the presence of secondary Na‐bearing plagioclase and chlorapatite indicate a metamorphic temperature &gt;600 °C. NWA 8418 contains kamacite, taenite, and troilite, and lacks magnetite and pentlandite. We propose that NWA 8418 be reclassified as a reduced CV4 chondrite, which makes it the first CV chondrite of petrologic type 4.