Understanding the origin and preservation of early mantle heterogeneities is essential for reconstructing Earth's accretion and early differentiation history. This can be investigated using the short-lived 146Sm-142Nd and 182Hf-182W isotope systems, which provide insights into large-scale differentiation processes through 142Nd and 182W anomalies in Earth's oldest rocks. In this study, we present 182W data for Theo's Flow, a thick, differentiated, mafic-ultramafic flow of tholeiitic affinity, as well as 147Sm-143Nd, 176Lu-176Hf, and 187Re-187Os isotope data and trace element concentrations, including highly siderophile elements, for Theo's Flow and closely spatially and temporally associated Pyke Hill komatiites, both from the -2.7 Ga old Kidd-Munro Assemblage of the Abitibi greenstone belt, Ontario, Canada. Theo's Flow samples are characterized by an average & micro;182W value of +6.7 +/- 2.7, which, together with the previously reported positive & micro;142Nd anomaly of +6.8 +/- 2.5, indicate longterm survival of mantle domains resulting from magmatic differentiation early in Earth's history. If it is assumed that the bulk silicate Earth evolved with a suprachondritic Sm/Nd ratio, anomalies for both elements can be explained by a single silicate differentiation event at -4.54 Ga. Alternatively, if the bulk silicate Earth evolved with a chondritic Sm/Nd ratio, a model fractionation age of -4.45 Ga is obtained. In this case, due to extinction of 182Hf by that time, the 182W anomaly would have to have been generated by another process, such as derivation from a mantle source characterized by a deficit in late accreted materials. Regardless of the timing of the early silicate differentiation, the preservation of both 182W and 142Nd anomalies in the 2.7 Ga old rocks highlights the survival of early-formed mantle domains for nearly 1.8 Gyr after Earth's formation. Comparison of isotopic and chemical data for Theo's Flow with those for the Pyke Hill and Boston Creek komatiites, which were argued to have all been derived from melting in a single mantle plume, provides evidence for the survival of early mantle heterogeneities on a plume scale.

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 epsilon 183 W ( 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.

Five enstatite chondrites, including two EH4 (Abee, Indarch) and three EL6 samples (Hvittis, Khairpur, Pillistfer), were investigated for their Hf-W isotope systematics to constrain the chronology and thermal evolution of their parent bodies and to assess the nature and extent of Hf-W fractionations among chondritic meteorites. The Hf-W ages range from -4.5 Ma to -10 Ma after CAI formation, where Pillistfer exhibits an older Hf-W age (-4.5 Ma) than the other two EL6 chondrites (-8.5-10 Ma), probably reflecting rapid cooling after impact excavation. The -8 Ma Hf-W age of the EH4 chondrite Indarch overlaps with those of the younger EL6 chondrites, indicating a similar cooling timescale despite the lower metamorphic grade. By contrast, Abee shows evidence for only partial resetting of the Hf-W system during metamorphism, and the 182W composition of Abee's metal still records the time of chondrule formation at -2 Ma after CAI formation. Thus, the thermal and cooling histories of enstatite chondrites do not appear to be a simple function of their metamorphic grade. Despite their distinct Fe-metal contents, EH and EL chondrites and their precursor material have uniform Hf/ W ratios. This most likely reflects the early and proportional removal of refractory metal and silicate components from the enstatite chondrite formation region, which left the Hf/W ratio unchanged. As such, the Hf/W ratio of enstatite chondrites provides a good estimate for the average composition of primitive chondritic material from the inner solar system. All carbonaceous chondrites except CI chondrites have higher Hf/W ratios, reflecting admixture of CAIs or metal-silicate fractionation during chondrule formation. Using the Hf/W ratio of enstatite chondrites, rather than carbonaceous chondrites, in the calculation of Hf-W core formation model ages makes these ages up to -0.7 Ma younger, shifting the core formation ages for non-carbonaceous iron meteorites closer to those of carbonaceous iron meteorites.

Major and trace element abundances, including highly siderophile elements, and 187Os and 182W isotopic compositions were determined for ca. 89 Ma mafic and ultramafic rocks from the islands of Gorgona (Colombia) and Curacao (Dutch Caribbean). The volcanic systems of both islands were likely associated with a mantle plume that generated the Caribbean Large Igneous Provence. The major and lithophile trace element characteristics of the rocks examined are consistent with the results of prior studies, and indicate derivation from both a chemically highly-depleted mantle component, and an enriched, or less highly-depleted mantle component. Highly siderophile element abundances for these rocks are generally similar to rocks with comparable MgO globally, indicating that the major source components were not substantially enriched or depleted in these elements. Rhenium-Os isotopic systematics of most rocks of both islands indicate derivation from a mantle source with an initial 187Os/188Os ratio between that of the contemporaneous average depleted mid-ocean ridge mantle and bulk silicate Earth. The composition may reflect either an average lower mantle signature, or global-scale Os isotopic heterogeneity in the upper mantle. Some of the basalts, as well as two of the komatiites, are characterized by calculated initial 187Os/188Os ratios 10-15 % higher than the chondritic reference. These more radiogenic Os isotopic compositions do not correlate with major or trace element systematics, and indicate a mantle source component that was most likely produced by either sulfide metasomatism or ancient Re/Os fractionation. Tungsten-182 isotopic compositions measured for rocks from both islands are characterized by variable mu 182W values ranging from modern bulk silicate Earth-like to strongly negative values. The mu 182W values do not correlate with major/trace element abundances or initial 187Os/188Os compositions. As with some modern ocean island basalt systems, however, the lowest mu 182W value (-53) measured, for a Gorgona olivine gabbro, corresponds with the highest 3He/4He previously measured from the suite (15.8 R/RA). Given the lack of correlation with other chemical/isotopic compositions, the mantle component characterized by negative mu 182W and possibly high 3He/4He is most parsimoniously explained to have formed as a result of isotopic equilibration between the mantle and core at the core-mantle boundary.

Carbonaceous chondrites are some of the most primitive meteorites and derive from planetesimals that formed a few million years after the beginning of the solar system. Here, using new and previously published Cr, Ti, and Te isotopic data, we show that carbonaceous chondrites exhibit correlated isotopic variations that can be accounted for by mixing among three major constituents having distinct isotopic compositions, namely refractory inclusions, chondrules, and CI chondrite-like matrix. The abundances of refractory inclusions and chondrules are coupled and systematically decrease with increasing amount of matrix. We propose that these correlated abundance variations reflect trapping of chondrule precursors, including refractory inclusions, in a pressure maximum in the disk, which is likely related to the water ice line and the ultimate formation location of Jupiter. The variable abundance of refractory inclusions/chondrules relative to matrix is the result of their distinct aerodynamical properties resulting in differential delivery rates and their preferential incorporation into chondrite parent bodies during the streaming instability, consistent with the early formation of matrix-poor and the later accretion of matrix-rich carbonaceous chondrites. Our results suggest that chondrules formed locally from isotopically heterogeneous dust aggregates, which themselves derive from a wide area of the disk, implying that dust enrichment in a pressure trap was an important step to facilitate the accretion of carbonaceous chondrite parent bodies or, more generally, planetesimals in the outer solar system.

Abstract Pallasites are mixtures of core and mantle material that may have originated from the core–mantle boundary of a differentiated body. However, recent studies have introduced the possibility that they record an impact mix, in which case an isotopic difference between metal and silicates in pallasites may be expected. We report a statistically significant oxygen isotope disequilibrium between olivine and chromite in main group pallasites that implies the silicate and metal portions of these meteorites stem from distinct isotopic reservoirs. This indicates that these meteorites were formed by impact mixing, during which a planetary core was injected into the mantle of another body. The impactor likely differentiated within ∼1–2 Myr of the start of the Solar System based on Hf–W chronology of pallasite metal, and we infer the age of the impact based on Mn–Cr systematics and cooling rates at between ∼1.5 and 9.5 Myr after Ca–Al-rich inclusions (CAIs). When combined with published slow subsolidus cooling rates for these meteorites and considering that several pallasite groups exist, our results indicate that such impacts may be an important stage in the evolution of planetary bodies.

On April 23rd, 2019, the Aguas Zarcas meteorite fall occurred in Costa Rica. Because the meteorite was quickly recovered, it contains valuable extraterrestrial materials that have not been contaminated by terrestrial processes. Our X-ray computed tomography (XCT) and scanning electron microscopy (SEM) results on various pre-rain fragments from earlier work (Kerraouch et al., 2020; 2021) revealed several distinct lithologies: Two distinct metal-rich lithologies (Met-1 and Met-2), a CM1/2 lithology, a Cl lithology, and a brecciated CM2 lithology consisting of different petrologic types. Here, we further examined these lithologies in the brecciated Aguas Zarcas meteorite and report new detailed mineralogical, chemical, isotopic, and organic matter characteristics. In addition to petrographic differences, the lithologies also display different chemical and isotopic compositions. The variations in their bulk oxygen isotopic compositions indicate that the various lithologies formed in different environments and/or under diverse conditions (e.g., water/rock ratios). Each lithology experienced a different hydration period during its evolution. Together, this suggests that multiple precursor parent bodies may have been involved in these processes of impact brecciation, mixing, and re-assembly. The Cr and Ti isotopic data for both the CM1/2 and Met-1 lithology are consistent with those of other CM chondrites, even though Met-1 displays a significantly lower epsilon Ti-50 isotopic composition that may be attributable to sample heterogeneities on the bulk meteorite scale and may reflect variable abundances of refractory phases in the different lithologies of Aguas Zarcas. Finally, examination of the organic matter of the various lithologies also suggests no strong evidence of thermal events, but a short-term heating cannot completely be excluded. Raman parameters indicate that the peak temperature has been lower than that for Yamato-793321 (CM2, similar to 400 degrees C). Considering the new information presented in this study, we now better understand the origin and formation history of the Aguas Zarcas daughter body. (C) 2022 Published by Elsevier Ltd.

As a moderately volatile, redox-sensitive chalcophile and siderophile element, Te and its isotopic composition can inform on a multitude of geochemical and cosmochemical processes. However, the interpretation of Te data from natural settings is often hindered by an insufficient understanding of the behavior of Te in high-temperature conditions. Here, we present the results of Te evaporation and isotopic fractionation in silicate melting experiments. The starting material was boron-bearing anorthite-diopside glass with 1 wt% TeO2. The experiments were conducted over the temperature range of 868-1459 degrees C for 15 min each, and at oxygen fugacities (logfO(2)) relative to the fayalite-magnetite-quartz buffer (FMQ) of FMQ-6 to FMQ+1.5, and in air. Evaporation of Te decreases with decreasing fO(2). For high-temperature experiments performed at > 1200 degrees C Te loss is accompanied by Te isotope fractionation towards heavier compositions in the residual glasses. By contrast, Te loss in experiments performed at temperatures < 1200 degrees C typically resulted in lighter Te isotopic compositions in the residues relative to the starting material. In air, Te evaporates as TeO2, whereas at lower oxygen fugacities we predict the evaporation of Te-2, using Gibbs free energy minimization calculations. In air, the experimentally determined kinetic isotopic fractionation factor for delta Te-128/126 at T > 1200 degrees C is alpha(K) = 0.99993. At reducing conditions, Te likely substitutes as Te2- for O2- in the melt structure and becomes increasingly soluble at highly reducing conditions. Consequently, Te evaporation is not predicted for volcanic processes on reduced planetary bodies such as the Moon or Mercury. (C) 2022 Elsevier Ltd. All rights reserved.

ORIGIN, AND EVOLUTION. I. Kerraouch1,2, A. Bischoff1, M. E. Zolensky2, J. L. Hellmann1, E. Wölfer1, A. J. King3, M. Patzek1, Y. Marrocchi4, A. Pack5, T. Ludwig6 and M. Trieloff6. 1Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm Str. 10, D48149 Münster, Germany (ikerraouch@uni-muenster.de). 2ARES, NASA Johnson Space Center, Houston TX, 77058, USA. 3Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK. 4Université de Lorraine, CNRS, CRPG, UMR 7358, Vandœuvre-lès-Nancy, 54501, France. 5Universität Göttingen, Geowissenschaftliches Zentrum, Goldschmidtstr. 1, Göttingen D-37077, Germany. 6Klaus-Tschira-Labor für Kosmochemie, Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany.

A coordinated study of the petrology, mineral chemistry, and bulk chemical and isotopic composition of the five ungrouped carbonaceous chondrites Coolidge, Loongana 001, Los Vientos (LoV) 051, Northwest Africa (NWA) 033, and NWA 13400 reveals that these meteorites have a similar set of properties that distinguishes them from the other carbonaceous chondrite groups and allows definition of the new Loongana (CL) group of carbonaceous chondrites. The basic characteristics of the investigated samples are: (1) Lithophile element ratios (e.g., Al/Mg, Si/Mg) are within the typical range of other carbonaceous chondrite groups. (2) Fe-Ni metal abundances are considerably higher than for CV, but similar to CR chondrites. (3) Chondrule size-frequency distributions are similar to CV, but dissimilar to CR chondrites. (4) The mean CAI abundance is similar to 1.4 vol%, i.e., lower than in CV but much higher than in CR chondrites. (5) Very low amounts of matrix (17-21 vol%), the lowest among the main carbonaceous chondrite groups (CI, CM, CO, CV, CR, CK). (6) Olivine is nearly equilibrated, with mean fayalite (Fa) values between 12.5 mol% (Loongana 001) and 14.7 mol% (NWA 13400) as a metamorphic effect. (7) Lower Al2O3 and higher MgO and Cr2O3 concentrations in matrix, compared to matrix in CV, CK, and CR chondrites. (8) Volatile elements (Mn, Na, K, Rb, Cs, Zn, Se, Te, Pb, Tl) are considerably depleted compared to all other main carbonaceous chondrite groups, reflecting the low matrix abundance. (9) Bulk O isotope compositions plot along the CCAM line (Delta O-17 -3.96 to -5.47 parts per thousand), partly overlapping with the CV and CK chondrite fields but including samples that are more O-16-rich. (10) Unique positions of CL values in the epsilon Cr-54-epsilon Ti-50 isotope plot, with epsilon Cr-54 values similar to CV, CK, and CO, but epsilon Ti-50 values similar to CR chondrites. All CL chondrites studied here are of petrologic type 3.9 to 4, indicating that they have been thermally metamorphosed on the parent body. The diagnostic features of CL chondrites detailed here provide a basis for identifying CL members of lower petrologic types. Such samples will be important for determining the pristine state of these meteorites and their components. (C) 2021 Elsevier Ltd. All rights reserved.

On September 12, 2019 at 12:49:48 (UT) a bolide was observed by hundreds of eye-witnesses from the Netherlands, Germany, Belgium, Denmark and the UK. One day later a small meteorite stone was found by accident in Flensburg. The presence of short-lived cosmogenic radionuclides with half-lives as short as 16 days proves the recent exposure of the found object to cosmic rays in space linking it clearly to the bolide event. An exceptionally short exposure time of similar to 5000 years was determined. The 24.5 g stone has a fresh black fusion crust, a low density of <2 g/cm(3), and a magnetic susceptibility of log chi = 4.35 (chi in 10(-9) m(3)/kg). The rock consists of relict chondrules and clusters of sulfide and magnetite grains set in a fine-grained matrix. The most abundant phases are phyllosilicates. Carbonates (similar to 3.9 vol.%) occur as calcites, dolomites, and a Na-rich phase. The relict chondrules (often surrounded by sulfide laths) are free of anhydrous silicates and contain abundant serpentine. Lithic clasts are also surrounded by similar sulfide laths partly intergrown with carbonates. Mn-53-Cr-53 ages of carbonates in Flensburg indicate that brecciation and contemporaneous formation of the pyrrhotite-carbonate intergrowths by hydrothermal activities occurred no later than 4564.6 +/- 1.0 Ma (using the angrite D'Orbigny as the Mn-Cr age anchor). This corresponds to 2.6 +/- 1.0 or 3.4 +/- 1.0 Ma after formation of CAIs, depending on the exact absolute age of CAIs. This is the oldest dated evidence for brecciation and carbonate formation, which likely occurred during parent body growth and incipient heating due to decay of Al-26. In the three oxygen isotope diagram, Flensburg plots at the O-16-rich end of the CM chondrite field and in the transition field to CV-CK-CR chondrites. The mass-dependent Te isotopic composition of Flensburg is slightly different from mean CM chondrites and is most similar to those of the ungrouped C2 chondrite Tagish Lake. On the other hand, Ti-50 and Cr-54 isotope anomalies indicate that Flensburg is similar to CM chondrites, as do the similar to 10 wt.% H2O of the bulk material. Yet, the bulk Zn, Cu, and Pb concentrations are about 30% lower than those of mean CM chondrites. The He, Ne, and Ar isotopes of Flensburg show no solar wind contribution; its trapped noble gas signature is similar to that of CMs with a slightly lower concentration of Ne-20(tr). Based on the bulk H, C, and N elemental abundances and isotopic compositions, Flensburg is unique among chondrites, because it has the lightest bulk H and N isotopic compositions of any type 1 or 2 chondrite investigated so far. Moreover, the number of soluble organic compounds in Flensburg is even lower than that of the brecciated CI chondrite Orgueil. The extraordinary significance of Flensburg is evident from the observation that it represents the oldest chondrite sample in which the contemporaneous episodes of aqueous alteration and brecciation have been preserved. The characterization of a large variety of carbonaceous chondrites with different alteration histories is important for interpreting returned samples from the OSIRIS-REx and Hayabusa 2 missions. (C) 2020 The Authors. Published by Elsevier Ltd.

Tellurium stable isotope compositions and abundances (δ128/126Te relative to SRM 3156) are reported for 43 ordinary, enstatite, and Rumuruti chondrites, which together with results from a companion study on carbonaceous chondrites are used to assess the origin of volatile element fractionations in chondrites. Whereas Te isotope variations among carbonaceous chondrites predominantly reflect mixing between isotopically light chondrules/chondrule precursors and CI-like matrix, Te isotope variations among non-carbonaceous chondrites mainly result from Te redistribution during parent body thermal metamorphism. The enstatite chondrites in particular display increasingly heavy Te isotopic compositions and decreasing Te concentrations with increasing degree of metamorphism, indicating migration of isotopically light Te from the strongly metamorphosed inner parts towards the cooler outer regions of the parent bodies. By contrast, ordinary and Rumuruti chondrites display less systematic Te isotope variations, implying more localized redistribution of Te during parent body thermal metamorphism.

A large, igneous‐textured, and 2 cm‐sized spherical object from the L5/6 chondrite NWA 8192 was investigated for its chemical composition, petrography, O isotopic composition, and Hf‐W chronology. The petrography and chemical data indicate that this object closely resembles commonly found chondrules in ordinary chondrites and is therefore classified as a “macrochondrule.* As a result of metal loss during its formation, the macrochondrule exhibits elevated Hf/W, which makes it possible to date this object using the short‐lived 182 Hf‐ 182 W system. The Hf‐W data provide a two‐stage model age for metal–silicate fractionation of 1.4 ± 0.6 Ma after Ca‐Al‐rich inclusion (CAI) formation, indicating that the macrochondrule formed coevally to normal‐sized chondrules from ordinary chondrites. By contrast, Hf‐W data for metal from the host chondrite yield a younger model age of ~11 Ma after CAIs. This younger age agrees with Hf‐W ages of other type 5–6 ordinary chondrites, and corresponds to the time of cooling below the Hf‐W closure temperature during thermal metamorphism on the parent body. The Hf‐W model age difference between the macrochondrule and the host metal demonstrates that the Hf‐W systematics of the bulk macrochondrule were not disturbed during thermal metamorphism, and therefore, that the formation age of such objects can still be determined even in strongly metamorphosed samples. Collectively, this study illustrates that chondrule formation was not limited to mm‐size objects, implying that the rarity of macrochondrules reflects either that this process was very inefficient, that subsequent nebular size‐sorting decimated large chondrules, or that large precursors were rare.

Compared to the composition of CI chondrites and the Sun, all other carbonaceous chondrites are variably depleted in volatile elements. However, the origin of these depletions, and how they are related to volatile loss during high-temperature processes within the solar nebula, are unclear. To better understand the processes that caused volatile element fractionations among carbonaceous chondrites, we obtained mass-dependent Te isotopic compositions and Te concentrations for a comprehensive set of samples from the major carbonaceous chondrite groups. The chondrites exhibit well-resolved inter-group Te isotope variations towards lighter isotopic compositions for increasingly volatile-depleted samples. The Te isotopic compositions and concentrations are also correlated with the mass fraction of matrix and with nucleosynthetic ε54Cr anomalies. Combined, these correlations indicate mixing between volatile-rich, isotopically heavy, and 54Cr-rich CI-like matrix with volatile-poor, isotopically light, and 54Cr-poorer chondrules or chondrule precursors. The Te-Cr isotopic correlation suggests that all carbonaceous chondrites contain CI-like matrix, and that chondrules and this CI-like matrix formed from isotopically distinct material originating from different regions of the disk. The only samples plotting off the Te-Cr correlation are CR chondrites, indicating that CR chondrules formed from different precursor material than chondrules from other carbonaceous chondrites, either because they formed at greater heliocentric distance and/or at a later time. Plots of volatile element abundances versus matrix mass fraction reveal that chondrules/chondrule precursors display CI-chondritic ratios for volatile elements with 50% condensation temperatures below ∼750 K, with an overall abundance of ∼0.13 × CI. Mixing between these two components, therefore, naturally results in CI-like ratios for these elements in all carbonaceous chondrites, in spite of different degrees of volatile depletion. A corollary of this observation is that the CI-like ratios of volatile elements in the bulk silicate Earth may result from the accretion of volatile-depleted materials and do not require accretion of CI chondrites themselves.

Introduction: Carbonaceous chondrites (CC) are pristine assemblages consisting of refractory inclusions, chondrules, matrix, and metal. As such, they provide fundamental constraints on processes within the solar accretion disk. The distinct CC groups exhibit chemical fractionations relative to the most primitive group, the CI chondrites. These fractionations depend on geochemical affinity and volatility [1,2]. However, in particular the depletion of volatile elements (50% condensation temperature (TC) <1250 K) and how this depletion relates to the formation of chondrules is poorly understood. The degree of volatile depletion is inversely correlated with the amount of matrix, suggesting that the CCs represent mixtures of volatile-rich matrix and volatile-poor chondrules or refractory inclusions [1,2]. More recent versions of this 'twocomponent model' strengthen the idea that volatile elements derive entirely from CI-like matrix, and that the volatile depletion among the CCs reflects different amounts of matrix [3,4]. However, other observations are more difficult to reconcile with the two-component model. For instance, some volatile elements exhibit mass-dependent isotope variations among the CC groups, indicating that these volatile elements derive from more than one component [e.g., 5,6]. Moreover, for non-volatile elements chondrules and matrix have complementary chemical and isotopic compositions [7,8], suggesting that both components derive from a common source, and not from two distinct sources. To better understand the origin of volatile fractionations in CCs, and the role of chondrules and matrix in producing these fractionations, we investigated the mass-dependent Te isotope fractionation among various CC groups. Tellurium is well suited for this task because it is a moderately volatile element (50% TC ~700 K), is variably depleted among the CCs, and exhibits isotope fractionation among chondrites [9]. Samples and analytical methods: Nineteen carbonaceous chondrites, including two CI, six CM, four CV, two CO chondrites, and the ungrouped chondrite Tagish Lake (TL) were investigated. Sample powders were spiked with a 123Te-125Te double spike, digested in HF-HNO3, and Te was purified using a three-stage column chemistry modified after [9,10]. The Te isotope measurements were performed using a Neptune Plus MC-ICPMS at Münster combined with a Cetac Aridus II. Results are reported in δ128/126Te as the per mil deviation from the NIST SRM 3156 Te standard. Results: The overall variation in δ128/126Te and Te concentrations among the CCs is ~0.2‰ and ~800 to ~2300 ng/g, respectively. Importantly, samples from a given CC group have indistinguishable δ128/126Te and display a narrow range of Te concentrations. Together with TL, the CC groups define a trend from heavy δ128/126Te and higher Te concentration to lighter δ128/126Te and lower Te concentration (Fig. 1).

Fifteen H, L, and LL ordinary chondrites of petrologic types 4-6 have been analyzed for Hf-W isotope systematics to constrain the chronology, internal structure, and thermal history of their parent bodies. For most samples coarse-grained metals plot below the isochrons defined by silicate-dominated fractions which consist of variable mixtures of silicate minerals with tiny metal inclusions. This offset results from an earlier Hf-W closure in the large metal grains and provides a new means for simultaneously determining cooling rates and Hf-W closure ages for individual samples. For most type 5 and 6 samples, cooling rates and Hf-W ages are inversely correlated, indicating that these samples derive from concentrically zoned bodies in which more strongly metamorphosed samples derive from greater depth. These data, therefore, provide strong evidence for a common 'onion shell' structure for the H, L, and LL chondrite parent bodies. The cooling rates and Hf-W ages of some type 5 and 6 chondrites overlap, indicating that the Hf-W systematics provide a more robust measure of the thermal history and burial depth of a given sample than the simple petrographic distinction between types 5 and 6. Two type 6 samples deviate from the correlation between cooling rates and Hf-W ages and cooled much faster than expected for their Hf-W age. These samples likely were excavated by impacts that occurred during high-temperature metamorphism and prior to complete closure of the Hf-W system at similar to 10 Ma after CAI formation. As these impacts would have disturbed the asteroid's cooling history, these samples likely derive from different bodies than samples with undisturbed cooling histories, implying that ordinary chondrites derive from more than just three parent bodies. The Hf-W data reveal that metal-silicate fractionation among the H, L, and LL groups occurred between similar to 2 and similar to 2.7 Ma after CAI formation and, hence, was about coeval to chondrule formation. As both metal-silicate fractionation and chondrule formation occurred prior to chondrite parent body accretion, there should be no ordinary chondrite chondrules that are younger than similar to 2.7 Ma. Finally, ordinary chondrite precursors had lower Hf/W ratios than carbonaceous chondrites, suggesting that inner and outer solar system materials, respectively, were chemically distinct even for refractory elements. (C) 2019 Elsevier Ltd. All rights reserved.

The abundances of highly siderophile elements (HSE: Re, Os, Ir, Ru, Pt, Pd), as well as Re-187-Os-187 and Hf-182-W-182 isotopic systematics were determined for separated metal, slightly magnetic, and nonmagnetic fractions from seven H4 to H6 ordinary chondrites. The HSE are too abundant in nonmagnetic fractions to reflect metal-silicate equilibration. The disequilibrium was likely a primary feature, as Re-187-Os-187 data indicate only minor open-system behavior of the HSE in the slightly and non-magnetic fractions. Hf-182-W-182 data for slightly magnetic and nonmagnetic fractions define precise isochrons for most meteorites that range from 5.2 +/- 1.6 Ma to 15.2 +/- 1.0 Ma after calcium aluminum inclusion (CAI) formation. By contrast, 182 W model ages for the metal fractions are typically 2-5 Ma older than the slope-derived isochron ages for their respective, slightly magnetic and nonmagnetic fractions, with model ages ranging from 1.4 +/- 0.8 Ma to 12.6 +/- 0.9 Ma after CAI formation. This indicates that the W present in the silicates and oxides was not fully equilibrated with the metal when diffusive transport among components ceased, consistent with the HSE data. Further, the W isotopic compositions of size-sorted metal fractions from some of the H chondrites also differ, indicating disequilibrium among some metal grains. The chemical/isotopic disequilibrium of siderophile elements among H chondrite components is likely the result of inefficient diffusion of siderophile elements from silicates and oxides to some metal and/or localized equilibration as H chondrites cooled towards their respective Hf-W closure temperatures. The tendency of Hf-182-W-182 isochron ages to young from H5 to H6 chondrites may indicate derivation of these meteorites from a slowly cooled, undisturbed, concentrically-zoned parent body, consistent with models that have been commonly invoked for H chondrites. Overlap of isochron ages for H4 and H5 chondrites, by contrast, appear to be more consistent with shallow impact disruption models. The W isotopic composition of metal from one CR chondrite was examined to compare with H chondrite metals. In contrast to the H chondrites, the CR chondrite metal is characterized by an enrichment in( 183)W that is consistent with nucleosynthetic s-process depletion. Once corrected for the correlative nucleosynthetic effect on W-182, the W-182 model age for this meteorite of 7.0 +/- 3.6 Ma is within the range of model ages of most metal fractions from H chondrites. The metal is therefore too young to be a direct nebular condensate, as proposed by some prior studies. (C) 2018 Elsevier Ltd. All rights reserved.