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As the Sun was forming, calcium–aluminum‐rich inclusions (CAIs) were the first rocks to have condensed in the hottest regions of the solar nebula disk. Carbonaceous chondrites (CCs) contain abundant CAIs but are thought to have accreted in the outer Solar System, requiring that CAIs must have been transported outward. Curiously, CAIs are rare in ordinary, enstatite, rumuruti, and kakangari chondrites, non‐carbonaceous chondrites (NCs), that likely formed in the inner Solar System. Thus, CAI abundances and characteristics can provide constraints on the early dynamical evolution of the disk. In this work, we address whether the hypothesis of an early‐formed proto‐Jupiter "opening a gap" in the disk can explain the dichotomy in the relative abundance of CAIs in CC and NC chondrites. We searched 76 NC meteorite sections to find 232 CAIs which have an average apparent diameter of 46 μm and comprise 0.01 area%, about half the size of and ~200 times less abundant than CC CAIs on average. Unlike CC CAIs, only 4% of the NC CAIs contain melilite and most contain alteration features suggesting that NC CAIs underwent pervasive fluid‐assisted thermal metamorphism on asteroidal parent bodies. However, based on NC CAI populations correlating with meteorite metamorphic grade, we argue that disk dynamics is likely the primary reason behind the existence of small (<100 μm) and rare NC CAIs. Our data support astrophysical models which suggest that, after outward transport of CAIs, formation of a gap in the disk trapped CAIs in the outer Solar System. [ABSTRACT FROM AUTHOR]

The Martian meteorites record a wide diversity of environments, processes, and ages. Much work has been done to decipher potential mantle sources for Martian magmas and their interactions with crustal and surface environments. Chlorine isotopes provide a unique opportunity to assess interactions between Martian mantle-derived magmas and the crust. We have measured the Cl-isotopic composition of 17 samples that span the range of known ages, Martian environments, and mantle reservoirs. The 37Cl of the Martian mantle, as represented by the olivine-phyric shergottites, NWA 2737 (chassignite), and Shergotty (basaltic shergottite), has a low value of approximately −3.8‰. This value is lower than that of all other planetary bodies measured thus far. The Martian crust, as represented by regolith breccia NWA 7034, is variably enriched in the heavy isotope of Cl. This enrichment is reflective of preferential loss of 35Cl to space. Most basaltic shergottites (less Shergotty), nakhlites, Chassigny, and Allan Hills 84001 lie on a continuum between the Martian mantle and crust. This intermediate range is explained by mechanical mixing through impact, fluid interaction, and assimilation-fractional crystallization. [ABSTRACT FROM AUTHOR]

Introduction: Calcium-aluminum-rich inclusions (CAIs) were the first solids to form in the nebular disk and can act as tracers for early disk processing. It is hypothesized that, also at an early time, the disk was separated into two isotopically distinct reservoirs (e.g., Mo and Cr isotopes), the carbonaceous chondrite (CC) outer Solar System region and the non-carbonaceous chondrite (NC) inner Solar System region [1]. If proto-Jupiter formed by ~1 Ma, it would have created a pressure gap to keep the CC and NC reservoirs separated [2]. CAIs are found in both CC and NC materials, however they are much more common in CC material [3]. CAIs from CC materials are also more wellstudied; over 12,000 CAIs have been found in systematic searches, while only ~350 NC CAIs have been found [e.g., 4]. Comparing the CAI modal abundance and sizes between NC and CC chondrites can inform us about disk dynamics in the early Solar System and can help to constrain the Jupiter gap model. Here, we focus on adding to the CAI populations and comparing their size distributions. We hypothesize that if the NC and CC CAI populations have similar size distributions, both populations were affected by similar disk processes. Methods: To find CAIs, we used the Tescan Vega-3 XMU Scanning Electron Micropscope (SEM) at UCLA. We first x-ray mapped thin sections (Ordinary, Enstatite, Rumuruti and carbonaceous Renazzo (CR) chondrites) with <5 µm per pixel resolution, locating CAI candidates using the Al map or Mg-Ca-Al composite maps. Then we identified CAIs using an energy dispersive spectrometer (EDS) upon locating minerals such as spinel, hibonite, Al-Ti-diopside, anorthite, melilite, and perovskite. We used ImageJ to determine the size of all scanned meteorite sections and CAIs. Results/Discussion: CAIs found. We systematically searched 76 NC sections and found 232 CAIs. Additionally, we searched one CR2 section (Acfer 395) and found 69 CAIs. The NC CAIs have an average apparent diameter of 46 µm (range from 4-382 µm) and a modal abundance of 0.009 area%. The CR2 CAIs have an average apparent diameter of 55 µm (range from 11-497 µm) and a modal abundance of 0.7 area%. These values are consistent with prior results [e.g., 3]. We directly compare our size distribution results to reported CV (Allende) and CM (Murchison) CAI size results [5]; 362 CV CAIs are 93 µm in average apparent diameter (30-1088 µm) and 325 CM CAIs are 36 µm in average apparent diameter (11-169 µm). Comparing CAI size distributions. In Fig. A, we show the average apparent diameter (data points) and diameter range (shaded areas) for literature (black) and our study (blue) for (n) chondrites. We agree with [e.g., 3] that CV and CK have the largest CAI size average and range. CO, CM, ungrouped, CR, and CH CAIs have average sizes <100 µm and the largest CAIs are <600 µm. NC CAIs have a more limited size range and slightly smaller average CAI sizes ~50 µm. We also compare the shape of CAI size distrubutions by plotting cumulative sizes (Fig. B). The linear trend of the distrubutions (in log-log space) suggests that NC and CC CAIs have lognormal size distributions. The slope of the linear trend indicates the power law exponent; we find the slopes to be between -1.5 to -1.9, except for the CR distribution which is shallower. In general, the NC and CC cumulative size shapes are rather similar. This evidence together suggests that, although the NC and CC average CAI sizes and CAI size ranges are distinct, a similar disk process allowed the formation of these CAIs, and the distribution did not change between CAI formation and accretion. The power law exponents imply that this process was coagulation and fragmentation in the hot, turbulent protoplanetary disk [6]. [ABSTRACT FROM AUTHOR]

Introduction: Calcium-aluminum-rich inclusions (CAIs) are the oldest objects in the solar system that formed 4.567 Ga ago [1,2] and experienced complex evolutionary histories before their accretion into the parent bodies. It is generally accepted that the largest, centimeter-sized CAIs are found in CV and CK chondrites, with CAI sizes in all other chondrites being smaller [3]. CAIs typically comprise 0.5-3 vol% in carbonaceous chondrites (CCs) that formed far from the Sun, but only < 0.1 vol% in enstatite and ordinary chondrites, collectively known as non-carbonaceous chondrites (NCs), that formed closer to the Sun [4]. Because CAIs are generally thought to have formed in the inner solar system, the fact that they were preferentially incorporated into CCs is puzzling. Asuka (A)-09003 and A-09535 represent a new type of carbonaceous chondrite, designated CA [5]. These CA chondrites have unique features: they share similarly high chondrule/matrix ratios with ordinary chondrites but resem-ble CO and CV chondrites in terms of the abundances of refractory inclusions (4-6 vol%) and oxygen isotopic com-positions [5]. With characteristic features of both NCs and CCs, the CA chondrites are in some sense transitional between materials that accreted in the inner solar system and those from the outer solar system. Here we present preliminary results of petrological characterizations of CAIs in CA chondrites. Methods: CAIs studied were identified in polished thin sections of Asuka 09003 and 09535, on loan from the National Institute of Polar Research. The petrographic observation and chemical analysis were performed by scanning electron microscopy (SEM, Tescan Vega) equipped with an energy dispersive spectrometer (EDS) at UCLA. Results: CAIs in both A-09003 and A-09535 are typically fine-grained inclusions (FGIs) up to several hundred micrometer in size. Based on mineralogy, the FGIs can be classified into four groups: (1) spinel-melilitepyroxene inclusions, (2) hibonite-spinel-melilite inclusions, (3) hibonite-spinel-melilite-grossite inclusions, and (4) pyroxene-rich inclusions. Spinel-melilite-pyroxene inclusions are irregularly-shaped and the most abundant type of CAIs in both A-09003 and A-09535 samples. Most of these inclusions have a spinel-rich core enclosed in melilite, both of which are rimmed by a complete or discontinuous layer of Ca-pyroxene. The inclusions contain fine-grained mixtures of Na-rich miner-als which appear to be alteration products replacing melilite. Hibonite-spinel-melilite inclusions are characterized by two types of morphologies. One has lath-shaped hibonite grains that are embedded in spinel and are subparallel to one another. Melilite occurs on the exterior of the inclusions. This morphology is similar to hibonite-spinel CAIs in the ALHA77307 (CO3.0) chondrite [6]. The other type is a layered structure of irregularly shaped nodule centers consisting of spinel that encloses hibonite and melilite that, in some nodules, has been partially converted into alteration products. Hibonite-spinel-melilite-grossite inclusions are either irregularly-shaped or round. These inclusions have similar mineralogy and texture to hibonite-spinel-melilite inclusions. MgO-rich and FeO-rich (Fe# (100 ' molar Fe/(Mg + Fe) > 75) spinel are both present in this type of inclusions. FeO-rich spinel shows a porous texture, while MgO-rich spinel does not. This type of inclusion has been found in the Kainsaz (CO3.2) chondrite [7]. Pyroxene-rich inclusions are rare and consist of Ca-rich pyroxene, anorthite, low-Ca pyroxene, and olivine. These observations are consistent with previous reports which showed similar types of inclusions in CO chondrites [7,8]. Thus, CA-CAIs and CO-CAIs may share similar formation histories. Further details will be presented at the conference. [ABSTRACT FROM AUTHOR]

Introduction: The Hayabusa2 mission returned approximately 5.4 g of highly aqueously-altered material resembling the CI (Ivuna-type) chondrites from the C-type asteroid Ryugu [1,2]. In order to understand the timing and duration of aqueous alteration which occurred on the Ryugu parent body, we measured the 53Mn-53Cr (t1/2 = 3.7 Myr) ages of carbonates in two Ryugu particles, A0037 and C0009. We then use these carbonate formation ages to constrain the accretion time and size of Ryugu's parent body. Methods: The 55Mn+/52Cr+ and 53Cr+/52Cr+ ratios of Ca-carbonate, dolomite, and breunnerite from particles A0037 and C0009 were measured using the CAMECA ims-1290 ion microprobe at UCLA. Analyses were performed using a 1 nA 16O3 - beam generated by an Oregon Physics Hyperion-II plasma ion source [3]. An MRP of ~5500 was used to separate 52Cr+ from 28Si24Mg+ and 53Cr+ from 52CrH+. Analysis spots were presputtered using an 8 × 8 or a 4 × 4 μm raster to remove surface Cr contamination before reducing the raster to 5 × 5 or 2 × 2 μm for analysis. The effective spot size was approximately 8 × 10 μm². The instrumental mass fractionation for the Cr isotopic ratio was corrected by comparison to repeated measurements of a terrestrial dolomite with trace amounts of Cr. The relative sensitivity factor (RSF) between Mn and Cr is defined as RSF = (55Mn/52Cr)True / (55Mn / 52Cr)SIMS and was determined using a combination of San Carlos Olivine and ion-implanted calcite, dolomite, and breunnerite standards. Results: The inferred initial 53Mn/55Mn ratios for Ryugu carbonates are 6.8 ± 0.5 × 10-6 (MSWD = 0.7) for A0037 dolomite and 6.1 ± 0.9 × 10-6 (MSWD = 0.3) for C0009 dolomite, Ca-carbonate, and breunnerite (all errors 2SE). When these ratios are calibrated relative to the initial 53Mn/55Mn of the D'Orbigny angrite [4], an 'anchor' sample with a well-defined Pb-Pb crystallization age [5,6], we calculate that A0037 and C0009 carbonates formed at 4566.9 ± 0.4 Ma and 4566.3 ± 0.4 Ma, respectively--that is, within the first 1.4 Myr after the CAI 'time zero' age of 4567.3 Ma [7]. This is significantly older than inferred from previous studies of CI chondrites [8,9]. Discussion: These old carbonate formation ages stand in contrast to ages obtained from carbonate in CI chondrites, most of which were thought to have formed 4-6 Myr after CAI formation [8,9]. We attribute this difference to our use of matrix-matched standards for the dolomite and breunnerite analyses. Had we corrected measured Mn+/Cr+ using a relative sensitivity factor derived only from analyses of calcite, we would have obtained ages of 3.0 Myr and 3.5 Myr after CAI formation for A0037 and C0009 carbonate respectively. Size and timing of accretion of the Ryugu parent body. Formation of carbonate within the first 1.4 Myr after CAI suggests a significantly different formation scenario than the large (>50 km) parent bodies accreting ~3-3.5 Myr after CAI which had been previously inferred for the parent bodies of CI chondrites [8,9]. Early accreted parent bodies would have had a high abundance of 26Al to drive water loss or even silicate melting and chemical differentiation if they cannot effectively conduct heat away by radiation. By modeling parent bodies accreting as mixtures of 50% chondritic material and 50% water ice, we find that parent bodies accreting before 1.4 Myr must be smaller than ~17 km in diameter for the internal temperature to remain below 400 K and avoid water loss. Alternatively, Ryugu material could have been formed in a larger progenitor body which was disrupted by impact before reaching peak temperatures. This multi-stage scenario is supported by petrographic and shock characteristics observed in Ryugu particles [10,11]. [ABSTRACT FROM AUTHOR]

- We report the 53Mn-53Cr systematics of three dolomite grains from two different CI1 clasts contained within the Kaidun meteorite breccia. Three internal isochrones result in initial 53Mn/55Mn ratios of (4.2 ± 0.4) × 10−6, (4.6 ± 1.3) × 10−6, and (5.2 ± 1.1) × 10−6. These initial values are consistent with those measured for dolomite in the Orgueil CI1 chondrite (; ) but significantly lower than the initial ratio determined by from a combination of different carbonate types within various lithologies of the Kaidun meteorite. We construct an accretion scenario for the Kaidun breccia by comparing the mineralogy and formation time scales of carbonates in the Kaidun CI1 lithologies to the analogous ones of the CI1 chondrite Orgueil. In Orgueil, dolomite precipitation precedes the formation of the first bruennerite grains by a few million years (; ). As the CI1 clasts in Kaidun lack breunnerite grains, and considering that aqueous alteration occurred prior to reaccretion of the various clasts onto the Kaidun parent body (e.g., ), we hypothesize that after rapid accretion and early aqueous alteration occurring within the first approximately 4 Myr after solar system formation, impact disruption of several asteroids and their reassembly into the Kaidun parent asteroid was complete within an additional approximately 2 Myr. This confirms that aqueous alteration, impact, and reaccretion of material in the asteroid belt were early processes that began contemporaneously with chondrule formation. [ABSTRACT FROM AUTHOR]