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The (187)Re-(187)Os isotopic systematics of many bulk chondrites plot well beyond analytical uncertainties of a primordial isochron. Limited variations in (187)Os/(188)Os, coupled with large variations in Re/Os ratios among chondrites, suggest that this apparently open-system behavior is a result of the comparatively recent gain or loss of Re and/or Os. In order to assess whether or not rapid alteration in the terrestrial environment could be responsible for open-system behavior in chondrites, four pieces of the Sutter’s Mill meteorite were examined for Os isotopic systematics and abundances of highly siderophile elements. Pieces SM1 and SM2 were collected prior to a rain event, within 2 days of the fall. Pieces SM51 and SM53 were collected after a rain event. There are significant but minor relative and absolute variations in the abundances of the highly siderophile elements, as well as (187)Os/(188)Os among the four pieces. Rhenium-Os isotopic data for SM1 and SM2 plot within analytical uncertainties of a primordial isochron, while powders made from SM51 and SM53 do not. These results suggest that interactions with rain caused some redistribution of Re, and to a lesser extent Os, within small pieces of the meteorite. Thus, Re-Os isotopic systematics of

Meteorites have been found on the small Misfits Flat dry lakebed near Stagecoach, Nevada (119.382W, +39.348N). Since the first find on Sept. 22, 2013, a total of 58 stones of weathering stage W2/3 with a combined mass of 339 g have been collected in 19 visits to the area. This small (3.3 × 3.6 km) lakebed is now a newly designated dense collection area (DCA). Most meteorites were found in a small 350 × 180 m area along the north shore and most are fragments of several broken individual stones. Three of these fragments were classified as an LL4/5 of shock stage S2, now named Misfits Flat 001, one of which (stone MF33) fell 8.1 ± 1.3 ka ago based on the 14C terrestrial age, assuming it came from a 20–80 cm diameter meteoroid. In addition, a small darkly crusted meteorite MF34, now named Misfits Flat 002, was found 820 m WSW from the main mass. This meteorite is classified as an LL5 ordinary chondrite with shock stage S4/5. The meteorite is saturated in 14C at 63 dpm kg−1, suggesting it originated from the center of a 0.5 m diameter meteoroid, or deep inside a ~1.0 m meteoroid, less than 300 yr ago. Accounts exist of a fireball seen at 13:15 UT on March 2, 1895, that are consistent with the find location of Misfits Flat 002.

Recent studies have shown that major meteorite groups possess their own characteristic 54Cr values, demonstrating the utility of Cr isotopes for identifying genetic relationships between the planetary materials in conjunction with other classical tools, such as oxygen isotopes. In this study, we performed Cr isotope analyses for whole rocks and chemically separated phases of the new CM2 chondrite, Sutter's Mill (SM 43 and 51). The two whole rocks of Sutter's Mill show essentially identical e54Cr excesses (SM 43 = +0.95 ± 0.09e, SM 51 = +0.88 ± 0.07e), relative to the Earth. These values are the same within error with that of the CM2-type Murchison (+0.89 ± 0.08e), suggesting that parent bodies of Sutter's Mill and Murchison were formed from the same precursor materials in the solar nebula. Large e54Cr excess of up to 29.40e is observed in the silicate phase of Sutter's Mill, while that of Murchison shows 15.74e. Importantly, the leachate fractions of both Sutter's Mill and Murchison form a steep linear anticorrelation between e54Cr and e53Cr, cross-cutting the positive correlation previously observed in carbonaceous chondrites. The fact that L4 acid leachate fraction contains higher 54Cr excesses than that of L5 step designed to dissolve refractory minerals suggests that spinel is not a major 54Cr carrier. We also note that L5 contains 53Cr anomalies lower than the solar initial value, suggesting it carries a component of nucleosynthetic anomaly unrelated to the 53Mn decay. We have identified five endmember components of nucleosynthetic origin among the early solar system materials.

Radiometric dating of secondary minerals can be used to constrain the timing of aqueous alteration on meteoritic parent bodies. Dolomite is a well-documented secondary mineral in CM chondrites, and is thought to have formed by precipitation from an aqueous fluid on the CM parent body within several million years of accretion. The petrographic context of crosscutting dolomite veins indicates that aqueous alteration occurred in situ, rather than in the nebular setting. Here, we present 53Mn-53Cr systematics for dolomite grains in Sutter's Mill section SM51-1. The Mn-Cr isotope data show well-resolved excesses of 53Cr correlated with 55Mn/52Cr ratio, which we interpret as evidence for the in situ decay of radioactive 53Mn. After correcting for the relative sensitivities of Mn and Cr using a synthetic Mn- and Cr-bearing calcite standard, the data yield an isochron with slope corresponding to an initial 53Mn/55Mn ratio of 3.42 ± 0.86 × 10−6. The reported error includes systematic uncertainty from the relative sensitivity factor. When calculated relative to the U-corrected Pb-Pb absolute age of the D'Orbigny angrite, Sutter's Mill dolomites give a formation age between 4564.8 and 4562.2 Ma (2.4–5.0 Myr after the birth of the solar system). This age is contemporaneous with previously reported ages for secondary carbonates in CM and CI chondrites. Consistent carbonate precipitation ages between the carbonaceous chondrite groups suggest that aqueous alteration was a common process during the early stages of parent body formation, probably occurring via heating from internal 26Al decay. The high-precision isochron for Sutter's Mill dolomite indicates that late-stage processing did not reach temperatures that were high enough to further disturb the Mn-Cr isochron.

Novato, a newly observed fall in the San Francisco Bay area, is a shocked and brecciated L6 ordinary chondrite containing dark and light lithologies. We have investigated the U-Pb isotope systematics of coarse Cl-apatite grains of metamorphic origin in Novato with a large geometry ion microprobe. The U-Pb systematics of Novato apatite reveals an upper intercept age of 4472 ± 31 Ma and lower intercept age of 473 ± 38 Ma. The upper intercept age is within error identical to the U-Pb apatite age of 4452 ± 21 Ma measured in the Chelyabinsk LL5 chondrite. This age is interpreted to reflect a massive collisional resetting event due to a large impact associated with the peak arrival time at the primordial asteroid belt of ejecta debris from the Moon-forming giant impact on Earth. The lower intercept age is consistent with the most precisely dated Ar-Ar ages of 470 ± 6 Ma of shocked L chondrites, and the fossil meteorites and extraterrestrial chromite relicts found in Ordovician limestones with an age of 467.3 ± 1.6 Ma in Sweden and China. The lower intercept age reflects a major disturbance related to the catastrophic disruption of the L chondrite parent body most likely associated with the Gefion asteroid family, which produced an initially intense meteorite bombardment of the Earth in Ordovician period and reset and degassed at least approximately 35% of the L chondrite falls today. We predict that the 470 Ma impact event is likely to be found on the Moon and Mars, if not Mercury.

–The Sutter’s Mill (SM) carbonaceous chondrite is a regolith breccia, composedpredominantly of CM2 clasts with varying degrees of aqueous alteration and thermalmetamorphism. An investigation of presolar grains in four Sutter’s Mill sections, SM43,SM51, SM2-4, and SM18, was carried out using NanoSIMS ion mapping technique. A totalof 37 C-anomalous grains and one O-anomalous grain have been identified, indicating anabundance of 63 ppm for presolar C-anomalous grains and 2 ppm for presolar oxides.Thirty-one silicon carbide (SiC), five carbonaceous grains, and one Al-oxide (Al 2 O 3 ) wereconfirmed based on their elemental compositions determined by C-N-Si and O-Si-Mg-Alisotopic measurements. The overall abundance of SiC grains in Sutter’s Mill (55 ppm) isconsistent with those in other CM chondrites. The absence of presolar silicates in Sutter’sMill suggests that they were destroyed by aqueous alteration on the parent asteroid.Furthermore, SM2-4 shows heterogeneous distributions of presolar SiC grains (12–54 ppm)in different matrix areas, indicating that the fine-grained matrix clasts come from differentsources, with various thermal histories, in the solar nebula.INTRODUCTIONThe Sutter’s Mill (SM) carbonaceous chondrite(CM2) fell in California on April 22, 2012. WeatherDoppler radars detected the falling meteorites, resultingin a fast recovery of some stones (Fries and Fries 2010;Jenniskens et al. 2012). The first stones found (SM 1-3)were recovered before rain and have minimal terrestrialweathering. Petrographic studies indicate that Sutter’sMill is a regolith breccia, composed of CM2 lithologieswith various degrees of aqueous alteration and thermalmetamorphism (Jenniskens et al. 2012; Zolensky et al.2012). Previous studies of acid residues show that someCM2 chondrites (e.g., Murchison, Murray) containabundant presolar material, mainly presolar SiC grains(e.g., Zinner 2013). Sutter’s Mill contains abundant fine-grained matrix areas, which are suitable for presolargrain searches. Previous studies have suggested thatdifferent secondary processes (aqueous alteration,thermal metamorphism) may preferentially destroypresolar mineral phases (presolar silicate/oxide, SiC)(e.g., Huss et al. 2003; Floss and Stadermann 2012).Here, we used NanoSIMS ion imaging to investigate thepresolar inventories of different SM fragments, forcomparison with the presolar grain abundances inMurchison and other primitive chondrites, and to gaina better understanding of the effects of secondaryprocesses on the preservation of presolar grains.SAMPLES AND EXPERIMENTALThe fragments analyzed in this study are SM43,SM51, SM2-4 (a subsample of SM2), and SM18 (forthe find locations in the strewn field, see Jenniskens

We determined the abundances and enantiomeric compositions of amino acids in Sutter's Mill fragment #2 (designated SM2) recovered prior to heavy rains that fell April 25–26, 2012, and two other meteorite fragments, SM12 and SM51, that were recovered postrain. We also determined the abundance, enantiomeric, and isotopic compositions of amino acids in soil from the recovery site of fragment SM51. The three meteorite stones experienced terrestrial amino acid contamination, as evidenced by the low d/l ratios of several proteinogenic amino acids. The d/l ratios were higher in SM2 than in SM12 and SM51, consistent with rain introducing additional l-amino acid contaminants to SM12 and SM51. Higher percentages of glycine, β-alanine, and γ-amino-n-butyric acid were observed in free form in SM2 and SM51 compared with the soil, suggesting that these free amino acids may be indigenous. Trace levels of d+l-β-aminoisobutyric acid (β-AIB) observed in all three meteorites are not easily explained as terrestrial contamination, as β-AIB is rare on Earth and was not detected in the soil. Bulk carbon and nitrogen and isotopic ratios of the SM samples and the soil also indicate terrestrial contamination, as does compound-specific isotopic analysis of the amino acids in the soil. The amino acid abundances in SM2, the most pristine SM meteorite analyzed here, are approximately 20-fold lower than in the Murchison CM2 carbonaceous chondrite. This may be due to thermal metamorphism in the Sutter's Mill parent body at temperatures greater than observed for other aqueously altered CM2 meteorites.

International audience; Sutter's Mill is a regolith breccia composed of both heavily altered clasts and more reduced xenoliths. Here, we present a detailed investigation of fragments of SM18 and SM51. We have characterized the water content and the mineralogy by infrared (IR) and thermogravimetric analysis (TGA) and the structure of the organic compounds by Raman spectroscopy, to characterize the secondary history of the clasts, including aqueous alteration and thermal metamorphism. The three methods used in this study suggest that SM18 was significantly heated. The amount of water contained in phyllosilicates derived by TGA is estimated to be approximately 3.2 wt%. This value is quite low compared with other CM chondrites that typically range from 6 to 12 wt%. The infrared transmission spectra of SM18 show that the mineralogy of the sample is dominated by a mixture of phyllosilicate and olivine. SM18 shows an intense peak at 11.2 mu m indicative of olivine (Fig. 1). If we compare SM18 with other CM and metamorphosed CM chondrites, it shows one of the most intense olivine signatures, and therefore a lower proportion of phyllosilicate minerals. The Raman results tend to support a short-duration heating hypothesis. In the ID/IG versus FWHM-D diagram, SM18 appears to be unusual compared to most CM samples, and close to the metamorphosed CM chondrites Pecora Escarpment (PCA) 91008 and PCA 02012. In the case of SM51, infrared spectroscopy reveals that olivine is less abundant than in SM18 and the 10 mu m silicate feature is more similar to that of moderately altered CM chondrites (like Murchison or Queen Alexandra Range [QUE] 97990). Raman spectroscopy does not clearly point to a heating event for SM51 in the I-D/I-G versus FWHM-D diagram. However, TGA analysis suggests that SM51 was slightly dehydrated as the amount of water contained in phyllosilicates is approximately 3.7 wt%, which is higher than SM18, but still lower than phyllosilicate water contents in weakly altered CM chondrites. Altogether, these results confirm that fragments with different secondary histories are present within the Sutter's Mill fall. The dehydration that is clearly observed for SM18 is attributed to a short-duration heating based on the similarity of its Raman spectra to that of PCA 91008. Because of the brecciated nature of Sutter's Mill and the presence of adjacent clasts with different thermal histories, impacts that can efficiently fragment and heat porous materials are the preferred heat source.

High-precision bulk aluminum-magnesium isotope measurements of calcium-aluminum-rich inclusions (CAIs) from CV carbonaceous chondrites in several laboratories define a bulk 26Al-26Mg isochron with an inferred initial 26Al/27Al ratio of approximately 5.25 × 10−5, named the canonical ratio. Nonigneous CV CAIs yield well-defined internal 26Al-26Mg isochrons consistent with the canonical value. These observations indicate that the canonical 26Al/27Al ratio records initial Al/Mg fractionation by evaporation and condensation in the CV CAI-forming region. The internal isochrons of igneous CV CAIs show a range of inferred initial 26Al/27Al ratios, (4.2–5.2) × 10−5, indicating that CAI melting continued for at least 0.2 Ma after formation of their precursors. A similar range of initial 26Al/27Al ratios is also obtained from the internal isochrons of many CAIs (igneous and nonigneous) in other groups of carbonaceous chondrites. Some CAIs and refractory grains (corundum and hibonite) from unmetamorphosed or weakly metamorphosed chondrites, including CVs, are significantly depleted in 26Al. At least some of these refractory objects may have formed prior to injection of 26Al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk. Bulk aluminum and magnesium-isotope measurements of various types of chondrites plot along the bulk CV CAI isochron, suggesting homogeneous distribution of 26Al and magnesium isotopes in the protoplanetary disk after an epoch of CAI formation. The inferred initial 26Al/27Al ratios of chondrules indicate that most chondrules formed 1–3 Ma after CAIs with the canonical 26Al/27Al ratio.

There is variability in the Mg isotopic composition that is a reflection of the widespread heterogeneity in the isotopic composition of the elements in the solar system at approximately 100 ppm. Measurements on a single calcium-aluminum-rich inclusion (CAI) gave a good correlation of ^(26)Mg/^(24)Mg with ^(27)Al/^(24)Mg, yielding an isochron corresponding to an initial (^(26)Al/^(27)Al)_o = (5.27 ± 0.18) × 10^(−5) and an initial (^(26)Mg/^(24)Mg)_o = −0.127 ± 0.032‰ relative to the standard. This isochron is parallel to that obtained by Jacobsen et al. (2008), but is distinctively offset. This demonstrates that there are different initial Mg isotopic compositions in different samples with the same ^(26)Al/^(27)Al. No inference about uniformity/heterogeneity of ^(26)Al/^(27)Al on a macro scale can be based on the initial (^(26)Mg/^(24)Mg)_o values. Different values of ^(26)Al/^(27)Al for samples representing the same point in time would prove heterogeneity of ^(26)Al/^(27)Al. The important issue is whether the bulk solar inventory of ^(26)Al/^(27)Al was approximately 5 × 10^(−5) at some point in the early solar system. We discuss ultra refractory phases of solar type oxygen isotope composition with ^(26)Al/^(27)Al from approximately 5 × 10^(−5) to below 0.2 × 10^(−5). We argue that the real issues are: intrinsic heterogeneity in the parent cloud; mechanism and timing for the later production of ^(16)O-poor material; and the relationship to earlier formed ^(16)O-rich material in the disk. ^(26)Al-free refractories can be produced at a later time by late infall, if there is an adequate heat source, or from original heterogeneities in the placental molecular cloud from which the solar system formed.