Meteoritics & Planetary Science 47, Nr 7, 1120–1138 (2012) doi: 10.1111/j.1945-5100.2012.01376.x

Chondrules: Precursors and interactions with the nebular gas

Roger H. HEWINS1,2* and Brigitte ZANDA1,2

1Laboratoire de Mine´ralogie et Cosmochimie du Muse´um, MNHN, 61 rue Buffon, 75005 Paris, France 2Earth & Planetary Science, Rutgers University, Piscataway, New Jersey 08854, USA *Corresponding author. E-mail: [email protected] (Received 11 June 2011; revision accepted 17 May 2012)

Abstract–Chondrule compositions suggest either ferroan precursors and evaporation, or magnesian precursors and condensation. Type I chondrule precursors include granoblastic olivine aggregates (planetary or nebular) and fine-grained (dustball) precursors. In carbonaceous chondrites, type I chondrule precursors were S-free, while type II chondrules have higher Fe ⁄ Mn than in ordinary chondrites. Many type II chondrules contain diverse forsteritic relicts, consistent with polymict dustball precursors. The relationship between finer and coarser grained type I chondrules in ordinary chondrites suggests more evaporation from more highly melted chondrules. Fe metal in type I, and Na and S in type II chondrules indicate high partial pressures in ambient gas, as they are rapidly evaporated at canonical conditions. The occurrence of metal, sulfide, or low-Ca pyroxene on chondrule rims suggests (re)condensation. In Semarkona type II chondrules, Na-rich olivine cores, Na-poor melt inclusions, and Na-rich mesostases suggest evaporation followed by recondensation. Type II chondrules have correlated FeO and MnO, consistent with condensation onto forsteritic precursors, but with different ratios in carbonaceous chondrites and ordinary chondrites, indicating different redox history. The high partial pressures of lithophile elements require large dense clouds, either clumps in the protoplanetary disk, impact plumes, or bow shocks around protoplanets. In ordinary chondrites, clusters of type I and type II chondrules indicate high number densities and their similar oxygen isotopic compositions suggest recycling together. In carbonaceous chondrites, the much less abundant type II chondrules were probably added late to batches of type I chondrules from different O isotopic reservoirs.

INTRODUCTION complex environment than a quiescent accretion disk. The abundance of chondrites indicates widespread melting in Chondrules are silicate particles with igneous textures some environment(s) in the protoplanetary disk, before the found in primitive meteorites (chondrites), accreted in the accretion of chondrules into their parent bodies. Definition protoplanetary disk. Their study began well over 100 yr of the formation conditions of chondrules therefore ago (e.g., Tschermak 1885) and has been intensive in the throws light on astrophysical or planetary processes, or 40 yr since the Apollo-Allende era, when meteoritics- both, occurring in the first few million years in the early cosmochemistry became a mature science. Interpretations solar system. In particular, it is unlikely that chondrule of chondrules’ origins are still controversial, however, melts could behave as closed systems in low pressure particularly since many chondrules post-date both nebular gases (e.g., Sears et al. 1996), whereas this is more calcium-aluminum-rich inclusion (CAI) and the earliest likely in planetary settings. Here, we consider evidence for differentiated bodies (Kleine et al. 2005, 2009; Halliday the nature of chondrule precursors; how chondrules and Kleine 2006). The early large-scale migration of interacted with ambient gas during melting, i.e., the protoplanets and non-accretionary collisions recently possible roles of evaporation and condensation during documented (Asphaug et al. 2006; Bottke et al. 2006; heating and cooling; and how ordinary and carbonaceous Walsh et al. 2011) place chondrule formation in a more chondrites differ in these respects.

The Meteoritical Society, 2012. 1120 Chondrule interactions with nebular gas 1121

Chondrule SiO2 McSween, 1977 Classification Scott and Taylor, 1983 Jones S, 1989, 1990, 1994, 1996 BSE images

IB IIB

IAB IIAB

IA IIA

MgO FeO

Fig. 1. BSE images of ferromagnesian olivine and pyroxene porphyritic chondrules of types IA (0.7 mm wide), IB (0.7 mm wide), IIA (0.6 mm wide), and IIB (0.8 mm wide) from Semarkona placed in an MgO–SiO2–FeO triangle so as to show their relative Mg, Fe, and Si contents.

CHONDRULE PROPERTIES fractionated in a systematic way (such as high T condensates). Alternately, the variability of bulk Most chondrules are ferromagnesian and are compositions primarily reflects exchanges with the classified as magnesian (type I) or ferroan (type II), with ambient gas such as evaporation of a chondritic (fayalite- olivine-dominant (A), intermediate (AB), and pyroxene- rich) composition (Sears et al. 1996; Cohen et al. 2004), dominant (B) subtypes (McSween 1977a; Scott and Taylor condensation onto a fractionated (forsterite-rich) 1983; Jones and Scott 1989; Jones 1990, 1994, 1996a; composition (Tissandier et al. 2002; Villeneuve 2010), or a Hewins 1997) in each type. We illustrate some typical more complex mixture of processes. porphyritic textures in Fig. 1, superimposed on a bulk Many chondrules have textures, including the composition triangle to show their relative Fe ⁄ Mg and presence of glass, indicating rapid crystal growth at near- SiO2 differences. The classification scheme can be liquidus temperatures, and the crystallization of extended to other textural types using mineral or bulk chondrule melts is well understood (Lofgren 1996; Hewins compositions (Hewins 1997). The proportions of different et al. 2005). ‘‘Flash’’ heating and cooling have been types of chondrule and the details of their compositions proposed for chondrules. However, experiments with very vary in different chondrite types, with type I dominant in rapid heating and cooling produce large temperature carbonaceous and type II in ordinary chondrites (Zanda gradients, insufficient crystal growth, and agglutinate-like et al. 2006). A major question is why we have a dispersion objects (fig. 13 in Hewins et al. 2005). Here, we show a of chondrule bulk compositions in MgO–SiO2–FeO type IIA chondrule with skeletal hopper olivine crystals composition space (Fig. 1), as shown by Radomsky and (Fig. 2a), very similar texturally to Apollo basalt 12009 Hewins (1990) and Cohen et al. (2004). Grossman and (Fig. 2b). Thus, the cooling conditions of this chondrule Wasson (1982) have suggested that this simply reflects a were not very different from those of some lunar basalts, random spectrum of precursor components that bearing in mind the different crystal growth rates in originated in condensation processes. However, in the liquids of different compositions. The cooling rates case of a closed system, such precursors would have to be estimated for most type II chondrules, based on either coarse-grained (and hence result from an anterior experiments matching textures and limited olivine zoning high-temperature episode; Hezel and Palme 2007) or data, are 10–1000 C (Lofgren 1996; Hewins et al. 2005). 1122 R. H. Hewins and B. Zanda

Fig. 2. Comparison of textures. (a) Type IIA porphyritic chondrule from Semarkona with hopper phenocrysts (BSE), which resemble those in lunar olivine vitrophyres. (b) Hopper olivine phenocryst and pyroxene dendrites in Apollo basalt 12009 (transmitted light). (c) Type IIA chondrule containing a large cluster of forsteritic olivine resembling type IA material (BSE), in Isheyevo CH ⁄ CBb chondrite, from Krot et al. (2007). (d) Semarkona type IIA chondrule with olivine phenocrysts and pyroxene dendrites in glass (BSE). Image widths are 0.6, 2.5, 0.25, and 0.4 mm, respectively.

Diffusion modeling of zoning profiles has enlarged this chondrites and ordinary chondrites, but ordinary ) range for PO down to at least 1 Ch 1 (Miyamoto et al. chondrites have the higher values. Echoes of these 2009). These cooling rates apply from the liquidus (1500– reservoirs appear in other work, e.g., Tenner et al. 1700 C) across the crystallization interval (at least (2011a) reported four clusters of olivine oxygen isotopic 300 C). Fewer experiments have been performed on type compositions in a CO3.0 equivalent to groups B, C, D, I chondrules, and their forsteritic olivine crystals are and E of Libourel and Chaussidon (2011). Isotopic almost unzoned, but their cooling rates appear to be compositions of olivine relict grains, olivine phenocrysts, similar to, or lower than, those of type II chondrules and igneous rims on chondrules in many chondrites (Wick 2010; Wick and Jones Forthcoming). Many type I suggest a reaction during heating and cooling to higher chondrules were heated well below their liquidus D17O values than those of the precursors (Wasson 2000; temperatures (Whattam and Hewins 2009). Reasonable Jones et al. 2004; Kunihiro et al. 2005; Krot et al. 2006; chondrule thermal histories are produced in the nebular Ruzicka et al. 2007), as do pyroxene grains crystallized shock wave model for chondrule formation (Desch and near chondrule margins (Libourel et al. 2006; Chaussidon Connolly 2002). et al. 2008). However, the opposite is seen in one type IA Many chondrules date from 1–3 Myr after CAI (Kita chondrule, where the olivine rims are more magnesian et al. 2000, 2005; Amelin et al. 2002; Amelin and Krot and enriched in 16O than the cores (Kita et al. 2010). In 2007; Villeneuve et al. 2009), although recent Pb–Pb general, such reactions may be explained by the assembly chronology (Connelly et al. 2011) suggests that the first of different amounts of solids and gas of different chondrules formed at the same time as CAI. Type I isotopic compositions, and subsequent equilibration chondrule olivines have D17O values in at least six (Krot et al. 2010a; Libourel and Chaussidon 2011). In clusters, named groups A–F, consistent with formation in some relatively 16O-rich CV and CR chondrules, increase six oxygen isotope reservoirs (Libourel and Chaussidon in D17O is related to the addition of SiO to the chondrules 2011); there is some overlap between carbonaceous (Chaussidon et al. 2008). However, for some chondrules Chondrule interactions with nebular gas 1123 in Tagish Lake (Russell et al. 2010), CO chondrites Fine-grained chondrules, often with outlines that are not (Tenner et al. 2011a), and CR chondrites (Schrader et al. rounded, tend to contain more sulfide and ⁄ or metal than 2011; Tenner et al. 2011b), even heavier oxygen isotope coarse-grained droplet chondrules (Campbell et al. compositions are associated with increasingly ferroan 2005). These chondrules are conceivably closer to their compositions, with two trends corresponding to precursors than common coarser grained ones. Their reservoirs B and C continuing into type II chondrules. textural and chemical differences between ordinary Semarkona has olivine in O isotope groups A, B, chondrites and carbonaceous chondrites (Zanda 2004) and C (Libourel and Chaussidon 2011). For other LL suggest different amounts of troilite in their chondrule chondrites, Kita et al. (2010) reported olivine oxygen precursors, in agreement with the bulk chemical isotopic compositions in both type I and type II compositions of these chondrites (Zanda et al. 2009), chondrules that are similar to those of group B type I while the sequences within each group suggest chondrules of Libourel and Chaussidon (2011). Olivine evaporative loss during the chondrule-forming events. in relic-free type II chondrules in CR chondrites In porphyritic type II chondrules, the most abundant (Connolly and Huss 2010; Schrader et al. 2011) have relict phase is forsteritic olivine (e.g., fig. 2c, from Krot D17O values corresponding to those of groups B and C in et al. 2007). Pyroxene (Jones 1996b; Hewins 1999; Hewins both ordinary chondrites and some carbonaceous et al. 2011) and spinel (Hewins et al. 2011) relics are chondrites and type I chondrules plot in groups B, C, known but much rarer, in part surely because they dissolve and D (Libourel and Chaussidon 2011). Thus, CR rapidly into type II melts at near liquidus temperatures. chondrules share the isotopic characteristics of ordinary The relict olivine has a wide range of compositions and and other kinds of carbonaceous chondrites. conceivably more than one source. Type I chondrules are Krot et al. (2007, 2010a) described unique chondrules an abundant possible source material in the chondrule- with skeletal blebby (barred) olivine (SO) along with forming regions. However, AOA have also been found in cryptocrystalline chondrules (CC) in CBb chondrites, and type IIs by Yurimoto and Wasson (2002). There is a these have later formation ages (4562.7 ± 0.5 Myr; Krot diversity of relict grain compositions even within a single et al. 2005a) than other chondrules. The transient heating type II chondrule. For example, we observed that a mechanism generating these chondrules is hypothesized chondrule in the CM Cold Bokkeveld, with normal olivine to be a collision of protoplanetary bodies, rather than core compositions Fa18 and higher, has two relict grains of some nebular process as hypothesized for common Fa0.7 ± 0.1 (n = 9) and Fa6.3 ± 0.7 (n = 10). This chondrules. In this hypothesis, the occurrence of CC strongly suggests heterogeneous precursors aggregated chondrules within zoned metal particles and the into a dustball, as advocated by Jones et al. (2005), enrichment in refractory elements of SO chondrules are although modification during the formation of type II consistent with an origin as liquid condensates and chondrules could also be considered (Villeneuve 2010). evaporative residues, respectively, formed in the impact Dark-zoned chondrules are very fine-grained and plume (Krot et al. 2005a, 2007, 2010a). Heavier Mg enriched in opaque minerals (mostly sulfides), especially isotopes in SO than CC chondrules (Gounelle et al. 2007) toward the outside (Dodd 1971; fig. 1c in Hewins et al. are consistent with this idea. 1997; fig. 1b in Hewins 1997). As they are not highly melted, they are potential precursors for PO chondrules PRECURSORS in OCs. However, ultra fine-grained precursors, such as nebular condensates, are incapable of producing the Many chondrules contain material that does not dominantly porphyritic textures of chondrules, appear to have crystallized from the chondrule melts. producing almost equally fine-grained olivine crystals in These objects indicate at least a part of the material experimental charges (Hewins and Fox 2004). They also existing at the time of chondrule melting, although the cannot reproduce the compositional heterogeneity of surviving population will be biased toward grains hardest chondrules in the case of a closed system (McSween to melt. These might be simply the largest grains of an 1977a; Hezel and Palme 2007) unless they are abundant phase in the precursor, or lithic inclusions, or fractionated themselves in a systematic way from the ‘‘xenocrysts’’ of rare precursor phases that are hard to beginning. However, in dark-zoned chondrules, besides melt, like forsterite in type II chondrules. Textures of some patches of fine-grained cryptoporphyritic material, which chondrules indicate incomplete melting, and these give the suggests that the precursor was largely fine dust (Hewins most information on the unprocessed material, both of et al. 1997), there is a great diversity of sizes of angular individual grains and of bulk composition, assuming that relicts. Chondrule precursors were probably a mixture of open system behavior is less in less melted objects. dust and large crystals in many cases. Other chondrules There is a spectrum of grain sizes in chondrules with low degrees of melting are aggregates mostly of accompanied by mineralogical and chemical changes. coarse crystals and sometimes chondrule fragments 1124 R. H. Hewins and B. Zanda

Fig. 3. BSE images of type I chondrules with outer zones of compact olivine (black), possibly formed by liquid phase sintering, surrounding glass-rich cores (medium gray): this polygonal olivine with triple junctions resembles GOA, suggesting that the latter might not be formed by planetary processes. (a) in NWA 4290 LL3.10 (a.k.a. Kelb Ellouz, courtesy B. Devouard). (b) in Vigarano CV3. (c) in Kaba CV3; all three chondrules are approximately 0.6 mm wide.

(Weisberg and Prinz 1996; Nettles et al. 2002), suggesting with low-temperature igneous phases within forsteritic that many chondrules especially in ordinary chondrites melts. The dissolution of CAI material within a are derived from chondrule debris, as advocated by chondrule would generate a melt on the Mg-poor side of Alexander (1996). the thermal divide (forsterite-anorthite cotectic), such The dominant relict material in type I chondrules, that plagioclase is stable (MacPherson and Huss 2005; especially in CV chondrites, is granoblastic olivine Tronche et al. 2007). This process is likely to have been aggregate (GOA) (Libourel and Krot 2007). GOA must significant for chondrules as testified by oxygen isotopes be either fragments of planetary rocks or highly annealed in the case of CR chondrites (Krot et al. 2006; Fig. 3) nebular material. Their granoblastic textures are and also by their chondritic Al ⁄ Si, Ti ⁄ Si, and Ca ⁄ Si characteristic of planetary materials (Libourel and Krot ratios (based on data from Alexander et al. [2008] for 2007), but somewhat similar textures appear as the outer ordinary chondrites and also from McSween [1977b] for shells of type I chondrules (Fig. 3) and appear to be of carbonaceous chondrites using appropriate correction nebular origin. Liquid phase sintering would promote the factors for broad beam EMP analyses). These chondritic growth of such textures, although there is little evidence of ratios imply that either condensation happened melt in GOA. Wasson and Rubin (2010) have suggested everywhere and CAI were converted to chondrules in that granoblastic textures in type I chondrules in CR some regions, or that some chondrites represent regions chondrites are due to long thermal pulses. Whether where evaporation was incomplete and Al, Ti, and Ca planetary or nebular, GOA produce porphyritic textures remained with forsterite in annealed residues. Both early by disruption during melting (Libourel and Krot 2007; primitive material (e.g., refractory inclusions) and late Whattam and Hewins 2009). Many chondrules appear to nebular material (chondrule debris) were thus available be disrupted GOA material, such that the ‘‘phenocrysts’’ as type I chondrule precursors. are really relict grains, and GOA are important precursors The properties of SO and CC chondrules in CH for IA PO chondrules. However, many type I chondrules, chondrites and the presence of GOA as well as fine- although not as fine-grained as dark-zoned chondrules, grained material within the precursors of various are too fine-grained to be derived from GOA precursors chondrules show that chondrules are unlikely to have (Hewins et al. 1997; Campbell et al. 2005; Whattam and formed by a unique mechanism and from a single type of Hewins 2009) and could have formed by dustballs. The precursor. Some chondrules in CV chondrites (Wood olivine in these chondrules might be derived from a 1996) and most chondrules in CR chondrites (Zanda primitive component, like AOA, or from debris from et al. 2002) may be interpreted as having formed from a other type I chondrules. In addition, the occurrence of spray of droplets in a dust-rich environment (Fig. 4). In ferroan olivine that experienced reduction to form dusty addition, as discussed above, it is likely that the forsterite in type I chondrules (Fredricksson 1969) precursors of chondrules in ordinary chondrites suggests that recycled type II chondrule material was contained S, whereas most of those of carbonaceous among the precursors of some type I chondrules. chondrites did not. This implies an effect of evaporation Some CAI were also incorporated into chondrules or––more likely––of fractional condensation on the (Krot et al. 2005b), in one case with a ‡2 Myr time gap. composition of chondrule precursors, independently of Such occurrences of CAI in chondrules are quite rare, any chemical changes that may subsequently have which could be explained by the ease of dissolving CAI resulted from the chondrule-forming event itself. Chondrule interactions with nebular gas 1125

2.0

1.8 S 1.6 Fe

1.4 Na

1.2

1.0

0.8

0.6

0.4

0.2 wt% S, Na & Fe norm. to Orgueil toFe norm. Na & S, wt% 0.0 0 50 100 150 200 Nominal Grain Size

Fig. 5. Concentrations of moderately volatile elements in Fig. 4. Composite type I chondrule in Renazzo CR2 chondrite, chondrules in Semarkona LL3.0 show a negative correlation with coarse-grained well-melted metal-bearing chondrules with nominal grain size, an indicator of extent of melting. This within finer grained less heated chondrule material set in fine- suggests that the more highly melted chondrules experienced grained matrix, suggesting formation of a spray of droplets in a more evaporation. dust-rich environment. White—metal; black—magnesian silicates in type I chondrules. as suggested above, they were derived from magnesian nebular condensates, subsequently processed or not, with Precursors that have experienced fractional lower temperature components added during chondrule condensation, or even fractional crystallization in early formation. parent bodies, might explain why the concentrations of moderately volatile elements Si, Fe, Na, and S vary EVIDENCE FOR LIMITED EVAPORATION significantly in chondrules. However, exchanges with the ambient gas during the chondrule-forming event are We interpreted very finest-grained Semarkona type I likely to be superimposed on precursor composition chondrules as those with initial properties least disturbed effects. For example, many OC type II chondrules are by melting, resembling original dustballs rather than not depleted in Na (Jones 1990; Hewins 1991) and they GOA precursors, and noted that they contained sulfide retained on the average 0.34 wt% S (Jones 1990). This rather than metal. We compared their compositions with might be better explained by heating in a low-pressure successively coarser grained, more extensively melted environment as suggested by the chondrule textural chondrules (Fig. 5): the moderately volatile elements S, sequences described in Campbell et al. (2005), followed Na, and Fe in bulk analyses decrease with increasing by recondensation upon cooling. We search below for grain size, consistent (Hewins et al. 1997) with an evidence of the evaporation and condensation during evaporation trend, and the most forsteritic olivine grains heating at low pressure predicted by experiment (e.g., have the lowest Mn concentrations. Fe is lost dominantly Tissandier et al. 2002; Cohen et al. 2004) and theory from silicate. As discussed in the next section, this idea is (Ebel and Grossman 2000; Alexander 2004; Davis et al. supported by the frequent presence of FeS-FeNi veneers 2005) in particular types of chondrules. The broader on chondrules presumably formed by the recondensation question is why there is the dispersion of MgO–SiO2– of the evaporated elements. An alternative explanation FeO compositions (Fig. 1): chondrules could be made for the volatile enrichment of the very fine-grained either by modifying a ferroan precursor primarily by chondrules is that these objects formed by aggregation of evaporation or reduction or a magnesian precursor partly melted particles that scavenged volatiles with an primarily by condensation. If primitive solar system dust efficiency that depended on their grain size (Scott and resembled anhydrous CI chondrite, i.e., minerals Krot 2005). However, the textures of metal-sulfide assumed to form from nebular condensates in which associations in type II chondrules and in the finer-grained fayalitic olivine formed by reaction of FeO with type I chondrules in ordinary chondrites demonstrate that enstatite, then evaporation and ⁄ or reduction during the S was already present within these chondrules when melting converted them into chondrules (Connolly et al. they melted. Thus, for ordinary chondrites, we deduce a 1994; Sears et al. 1996; Cohen et al. 2004). Alternatively, mildly ferroan dustball precursor for many type I 1126 R. H. Hewins and B. Zanda

) chondrules, and evaporation as a dominant process. Iron of 1.3 · 10 5 bar, Fe metal was never observed (Cohen evaporated from silicate melt into hydrogen-rich gas and Hewins 2004; Cohen et al. 2004). The survival of Fe- would recondense as metal. Metal and silicate metal in chondrules means less drastic conditions. For compositions in type I chondrules from CR chondrites example, it survives for 6 h at 1580 C at 1 atm H2-CO2 were also interpreted as evidence for Fe evaporation (IW-3), before evaporating (Cohen and Hewins 2004). during melting followed by its recondensation onto The combination of Fe-metal and forsteritic olivine in chondrule surfaces along with the other moderately many type I chondrules is thus incompatible with volatile siderophile elements (Connolly et al. 2001; evaporation of any ferroan precursor, such as anhydrous Humayun et al. 2002, 2010; Zanda et al. 2002; Campbell CI precursor, if the ambient pressure is low. The presence et al. 2005). of Fe metal in chondrules requires some combination of )5 Evaporation experiments at PH2 of 1.3 · 10 bars high total pressure Ptot, high PFe, and ⁄ or relatively short (Cohen and Hewins 2004; Cohen et al. 2004) have heating time. produced some but not all properties of type I Isotopic data also argue in favor of limited chondrules. At temperatures that produce extensive evaporation from chondrule melts or back reaction from melting within chondrules at total pressures of less than the gas: isotopic mass fractionation is the signature of 1 bar, the stable form of most elements including Fe and free evaporation and if chondrules formed at nebular S is vapor (e.g., Wood and Hashimoto 1993). In free pressures, the absence of mass fractionation in evaporation experiments at 1350 and 1580 C (Cohen chondrules (e.g., Alexander et al. 2000) must be and Hewins 2004), Fe is lost rapidly from melted troilite, explained. A potential solution is melting in solid- and residual Fe metal, and more slowly from silicates. enriched nebular environments (Hewins 1989, 1991), Sears et al. (1996) proposed that chondrule compositions where isotopic exchange between gas and liquid is evolved by evaporation first of Fe then of Si from possible (Alexander 2004; Cuzzi and Alexander 2006). silicates to produce the trend from IIA to IB to IA Kinetic modeling of chondrule formation by shock wave chondrules in Fig. 1. The loss of S and Fe from different shows extensive evaporation and recondensation of type I chondrules with more extensive melting has been alkalis (Fedkin et al. 2011, 2012). We discuss below documented (Hewins et al. 1997; Zanda et al. 2002). evidence for (re)condensation and the particular case of Evaporation experiments (Cohen et al. 2004) reproduce ordinary chondrite type II chondrules, which carry Ca-rich bulk and olivine compositions similar to those of evidence for both loss and gain of Na during their type I chondrules (Jones and Scott 1989). The Ca-rich formation. forsterite is due to equilibrium partitioning from the liquid (Libourel 1999), no matter how that liquid EVIDENCE FOR CONDENSATION composition is achieved. If type I chondrules had been formed by evaporation of a ferroan precursor at nebular Type II chondrules are chondritic in alkalis (Hewins pressures, this would have required long heating times. 1991) and even at 1 atm, Na could not be retained at However, while these aspects of natural type I chondrule cooling rates required for the production of chondrule might be related to evaporation, the experiments failed textures (Yu and Hewins 1998). Chondrules should be to reproduce some of their major features, such as devoid of alkalis, as well as of sulfide and metal, if they pyroxene near the rim, possibly formed by condensation experienced any evaporation of FeO (Yu et al. 2003; (see below) and kamacite globules, which require non- Cohen and Hewins 2004; Cohen et al. 2004), yet even canonical conditions (see below). type I chondrules contain moderate concentrations of Na Silicate charges containing troilite heated at 1350 C and metal may be abundant. K isotopes are fractionated )5 and PH2 of 1.3 · 10 bars (

pyroxene near the rims as a result of SiO condensation, 1.0 suggests that IAB chondrules could be a result of this Semarkona Type IIA chondrule olivine CM chondrites process (Tissandier et al. 2002). The IA–IAB–IB textural 0.8 y = 0.02x + 0.05 association is found in both ordinary chondrites and R2 = 0.77 carbonaceous chondrites (Scott and Taylor 1983), 0.6 indicating that SiO condensation into chondrules is a general process (Libourel et al. 2006). wt% MnO 0.4 y = 0.01x + 0.05 R2 = 0.67

Fe–Mn Fractionation in Type II Chondrules: Evidence for 0.2 Condensation in the Chondrule-Forming Event

0.0 Villeneuve (2010) has proposed that type II 0102030405060 chondrules were formed from type I chondrule material, wt% FeO partly by oxidation of metal (which he demonstrated Fig. 6. Olivine in chondrules in ordinary chondrites and CM experimentally), and by addition of species such as FeO chondrites (Cold Bokkeveld, Mighei, and Murchison) have and SiO from the gas during chondrule formation. The different FeO ⁄ MnO ratios and enrichment trends, indicating common occurrence of relict forsterite of type I that they formed in reservoirs of different oxidation state. The trends converge in the region of type I chondrule olivine and composition strongly supports this. relict grain compositions. Type II chondrule formation may Berlin et al. (2011) have shown that olivine in type have involved condensation of FeO and MnO onto type I IIA chondrules in ordinary chondrites, CR, and CO precursors. chondrites has distinctly different Fe ⁄ Mn ratios. We illustrate a similar difference between OC and CM like Na and Si can diffuse through the silicate melt chondrites in Fig. 6 with our analyses of IIA olivine in toward the chondrule center. However, S, Fe, and other Semarkona and Cold Bokkeveld, Mighei, and chalcophile and siderophile elements do not dissolve Murchison. The different average Fe ⁄ Mn ratios of the easily in chondrule melts and therefore build opaque olivines indicate that the two groups of chondrules were veneers on chondrule surfaces when recondensing. formed in different reservoirs, with different redox conditions and possibly extent of condensation into the Opaque Veneers Around Chondrules in CR and Ordinary chondrule melts or precursors. The question of interest is Chondrites: Evidence for Recondensation Following why the chondrule olivine (and bulk) compositions are Evaporation so dispersed and more so in carbonaceous chondrites than ordinary chondrites. Metal (and infrequently sulfide) veneers, i.e., Oxidation of Fe from metal would dilute MnO and concentrations of grains on and near rims, are found on would not create a positive correlation of MnO and FeO. many of the coarse-grained type I chondrules in CR As the two trends in Fig. 6 exhibit positive correlations, chondrites (Fig. 7a). The distribution of volatile oxidation of Fe from metal can only have played a limited siderophile elements, such as Cu, Pd, and Au, observed role, such as causing the jump from type IA olivine by Humayun et al. (2002, 2010) shows that at least one composition to the most magnesian type IIA chondrules. population of chondrule rim metal is depleted in As the chondrules are independent melt droplets, they refractory siderophiles and enriched in volatile cannot be related by crystal fractionation. The siderophiles relative to interior metal. This supports the correlations are thus the signature of volatility-related proposal of Connolly et al. (2001) that some of the rim processes. They could conceivably reflect either the metal can be explained by recondensation of a vapor evaporation of Fe and Mn from the molten chondrules or derived from the evaporation of chondrules onto the the condensation into the chondrule melts during cooling chondrule surfaces (Connolly et al. 2001; Humayun et al. of Fe and Mn present in the gas, previously derived from 2002; Zanda et al. 2002), an interpretation which is also chondrules or dust by evaporation. However, the trends qualitatively consistent with the zoning of Ni and Co converge in the general area of the compositions of type I reported by Lee et al. (1992) as pointed out by Campbell chondrule olivine and relict forsteritic grains in type II et al. (2005). chondrules. This, along with the very presence of the Type I and type II chondrules in ordinary chondrites relict forsteritic grains, suggests condensation onto type also exhibit opaque veneers, but these contain a large I material as the dominant process. amount of S (Fig. 7b). In fact, less than one fourth of the Moderately volatile elements lost during the melting S in Semarkona is contained within its fine-grained matrix event are expected to recondense into the chondrule on and less than 2% within its chondrules. S in Semarkona is cooling (e.g., Fedkin et al. 2008). Lithophile elements mostly found in the opaque veneers and in large metal– 1128 R. H. Hewins and B. Zanda

formed in reservoirs lacking the complement of elements not in the precursors, in particular S for carbonaceous chondrites. These observations on metal and sulfide a suggest limited evaporation, and recondensation of the moderately volatile elements, due to high partial pressures, or total pressure. Both evaporation and condensation are expected theoretically, with chondrule melts approaching CMAS liquid compositions temporarily for extreme conditions (Fedkin et al. 2008), but effects due to recondensation may be more obvious than the earlier evaporation. In the next section, we search for evidence of both processes in the same suite of chondrules.

b EVAPORATION AND CONDENSATION OF NA IN TYPE II CHONDRULES

The presence of volatiles in chondrules is a potential key to their formation conditions and the ambient gas. Even at 1 atm, Na cannot be retained at cooling rates required for chondrule textures if PNa is low (Yu and Hewins 1998). Most chondrules have higher FeO and Na2O contents higher than expected for formation in Fig. 7. BSE images of veneers formed by condensation on canonical solar nebular gas, suggesting formation of melt chondrules. (a) Metal veneers on chondrules in CR2 Renazzo. droplets at high PNa due to extensive vaporization of (b) Sulfide veneers on chondrules in LL3.0 Semarkona. accompanying material in a particle-rich clump (Hewins White—metal or sulfide; gray—ferroan silicates in matrix (particularly in a) or type II chondrules (particularly in b); 1989). We estimated the size of these clumps to be about black—magnesian silicates in type I chondrules. This figure 1000 km (Sahagian and Hewins 1992). Type II also displays the fundamental difference between ordinary and chondrules in Semarkona were found to be close to carbonaceous chondrites. Semarkona chondrules are chondritic (Orgueil or Semarkona) in Na ⁄ Al ratio ‘‘clustered’’ together, while the chondrules in Renazzo (some of (Hewins 1991) as confirmed by more recent analyses: which are ramified and composite-looking) are separated by an abundant fine-grained matrix. The image is 1.2 cm wide for Fig. 8 shows that analyses of type IIA and IIAB Renazzo (top); 0.5 cm wide for Semarkona (bottom). chondrules from Semarkona by Jones (1990, 1996a), Alexander et al. (2008), Hewins et al. (2012), and Hewins sulfide associations, which are likely to have fallen from and Zanda (unpublished data) plot close to the chondrule surfaces (Zanda and Bourot-Denise, personal chondritic ratio (Orgueil; Jarosewich 1990). The type IIA communication). The opaque veneers on 3 chondrules chondrules of Jones (1990) have a slightly higher Na ⁄ Al often contain intimate troilite-pentlandite intergrowths ratio, close to 1, suggesting the presence of albite in the derived from Ni-rich monosulfide solid solution. precursors (Hewins 1991). The observation of chondritic Experiments by Lauretta et al. (1997) show that Na abundances in chondrules led to the idea that the condensate sulfide made from the reaction of gaseous H2S melts became stabilized by the local concentration of with kamacite contains significant dissolved Ni. We thus dust or ice in the disk (Hewins 1991), so that small interpret these veneers as the result of S (and Fe) amounts of evaporation during heating gave liquid–gas evaporation from chondrules followed by their equilibrium (e.g., Wood 1996). In this case, there would recondensation on chondrule surfaces. Condensate sulfide be no need for very short duration heating–cooling is afterward commonly modified by alteration and ⁄ or cycles. Lewis et al. (1993) showed experimentally that Na )6 low-temperature metamorphism in chondrites (Zanda could be retained in chondrule melts with PNa  10 et al. 1995). atm, whereas Mathieu (2009) has determined Na The difference between type I chondrules in solubilities for a wide range of melt compositions with a )4 ordinary and carbonaceous chondrites in the nature of PNa of 1.25 · 10 atm. However, such high PNa values, their veneers simply reflects the difference in their which would have prevented evaporation, seemed to precursors, which contained no S in carbonaceous require an implausible level of dust or ice enrichment in chondrites as suggested by Zanda et al. (2009) and the disk (Hewins 1997; Yu and Hewins 1998) and this discussed above. It also suggests that the chondrules still presents problems (Fedkin et al. 2008, 2011, 2012). Chondrule interactions with nebular gas 1129

3 Semarkona Type II chondrules Orgueil

2

CA IIA MESOSTASIS CA IIAB RJ IIA wt% Na2O MELT CHANNEL 1 RJ IIAB RH IIA RH IIAB OPEN RH IIA* INCLUSION RH IIAB* 0 01234567 wt% Al2O3 INCLUSION WITH BUBBLE

Fig. 8. Al2O3 and Na2O concentrations show that Semarkona type II chondrules have chondritic Na concentrations. Data RJ are from Jones (1990, 1996a), CA from Alexander et al. (2008b), RH from Hewins et al. (2012), and RH* our unpublished data. The reference line is for Orgueil (Jarosewich Fig. 9. Distribution of silicate melt in type IIA chondrule 64– 1990). 65 in Semarkona, showing mesostasis, melt channels, open inclusions, and glass inclusions in olivine.

The concentration of Na in minerals such as olivine can potentially indicate if they were in equilibrium with 16 Type I trend of Si addition the chondrule melt, in turn giving an idea of PNa when the Semarkona Type IIA 64- (Libourel and Krot, 2006) chondrules melted and cooled. Alexander et al. (2008a) determined Na concentrations in chondrule olivine and 12 melts, and estimated very high PNa. We continued their inclusions work (Hewins et al. 2012) using porphyritic Semarkona melt channels embayments type II chondrules, adding new approaches: we looked at 8 mesostasis the Na contents of glass inclusions in olivine, we wt% Al2O3 considered olivine–melt equilibrium using three recent olivine fractionation 64 inclusions experimental studies on the Na partitioning (Borisov 4 et al. 2008; Kropf 2009; Mathieu 2009), and we compared 64-65 mesostasis 64-65 bulk observed and calculated liquids resulting from fractional bulk composition olivine 64-65 olivine crystallization using PETROLOG (Danyushevsky 2001; 0 Danyushevsky and Plechov 2011). The figures and 35 45 55 65 75 wt% SiO2 discussion below are based on the results of Hewins et al. (2012). Fig. 10. The correlation of SiO2 and Al2O3 is explained by Figure 9 shows a type IIA chondrule with liquid their enrichment in melt due to olivine crystallization in Semarkona type IIA chondrule 64–65, with no evidence for preserved as glass in various environments. These include addition of SiO from the gas. primary melt inclusions trapped in olivine, melt channels in olivine sometimes seen to connect to the exterior, open inclusions (Faure and Schiano 2005) or embayments on type II chondrules indicate that they were extensively crystal boundaries, and free mesostasis. The mesostasis melted and crystallized olivine, but do not indicate how in Fig. 9 contains only a few tiny dendrites, but in other the chondrule bulk compositions arose. chondrules, there are large pyroxene dendrites (Fig. 3d). In Fig. 11, we show the dispersion of mesostasis Figure 10 compares the compositions of these liquids. Na2O and SiO2 concentrations due to the effects of There is a trend of increasing Si and Al through the initial liquid composition and the crystallization of various glass compositions, consistent with fractional olivine ± pyroxene. The IIA liquids crystallize olivine crystallization of olivine from a liquid with the bulk only, and are enriched in both Na and Si. The relatively composition of the chondrule. This is unlike the situation low Si but high Na and Al contents of IIAB mesostases for type I chondrules, where the pattern of glass are explained by the crystallization of orthopyroxene compositions is inconsistent with olivine crystallization, with similar Si to the liquids. However, many mesostases but shows addition of silica, presumably from ambient have higher Na2O concentrations than predicted by gas, to an initial liquid enriched in refractory elements PETROLOG calculations. Melt inclusions in olivine are (Tissandier et al. 2002; Krot et al. 2004). The data for Si-rich, because after being enclosed in olivine, they have 1130 R. H. Hewins and B. Zanda

12 12 IIA bulk olivine IIA mesostases Type II chondrules, Semarkona 10 IIAB bulk inclusions IIAB mesostases IIA 9 melt inclusions IIA(B) 8 cryst olivine only IIAB equil pyroxene late pyroxene 6 mesostases 6 wt% Na2O wt% 4 wt% Na2O

3 2

0 olivine pyroxene 35 45 55 65 75 0 wt% SiO2 0369121518 wt% Al2O3 Fig. 11. Compositions of Semarkona IIA and IIAB bulk Fig. 12. Average compositions of Semarkona IIA, IIA(B), and chondrules, mesostases, and melt inclusions in olivine. IIAB bulk chondrules, mesostases, and melt inclusions in Fractionation trends resulting from crystallization of olivine olivine. Compared with daughter liquids calculated for from IIA were calculated using PETROLOG. For type IIAB fractional crystallization, melt inclusions have lower Na chondrules, three calculations were made: crystallization of contents, suggesting evaporation, and mesostases higher Na olivine only, olivine followed by equilibrium pyroxene, and contents, suggesting recondensation, i.e., open system behavior. olivine followed by late nucleated pyroxene.

Kropf and Mathieu have almost identical coefficients for continued to crystallize metastable olivine rather than Na partitioning in the Fe-free system. Mathieu defined nucleating pyroxene. Their Na concentrations are much the effect of Fe in olivine on Na partitioning, using data lower than expected for fractional crystallization of for terrestrial rocks in which evaporative loss is not an olivine from the apparent parent liquid. (Analyses of issue. We use his expression to calculate the Na content of melt inclusions shown in Fig. 11 are not shown here, melts in equilibrium with our olivines. We see that the because prior exposure to the electron beam rims and glasses are very close to being in equilibrium, compromised the Na data.) whereas cores are not. In particular, the IIA bulk Average values for Al2O3 and Na2O of bulk, compositions have on average only a third of the Na mesostasis, and inclusion melts are plotted in Fig. 12. expected for equilibrium partitioning. Thus, we conclude We distinguish type IIA(B) chondrules, an olivine- that chondrules lost Na by evaporation during olivine dominant IIAB resembling chondrule C120 of Jones crystallization, leading to the formation of melt inclusions (1996a) here, although they were included with type that are less enriched in Na than expected for fractional IIAB in Fig. 11. Error bars are one standard deviation. crystallization. Addition of Na by condensation after We show calculated daughter liquids for three typical inclusions were cut off inside olivine is required to explain compositions. Those which crystallize pyroxene (IIA[B] the Na-rich mesostasis compositions and the olivine rim and IIAB) show slight deviations from the olivine-only compositions. trend (IIA) toward higher Na, because Al is more The record of olivine and glass Na concentrations is compatible in pyroxene than Na. Figure 12 shows that thus consistent with evaporation at high temperature inclusions have lower Na and mesostases higher Na than followed by condensation at low temperature. This is consistent with fractional crystallization of the bulk sequence has been predicted for chondrules heated in chondrule compositions. nebular shocks, e.g., Fedkin et al. (2008). Exchange of The data in Hewins et al. (2012) may be used to Na between melt and gas means that Na in the bulk investigate Na partitioning between olivine and melt. We composition after the chondrule-forming event was not initially make the conventional assumption that olivine its original value. cores were in equilibrium with liquids of bulk chondrule composition and calculate apparent partition coefficients CHONDRULE RELATIONSHIPS DNa(Ol ⁄ Liq). We assume that rim olivine crystallized from residual melt in the mesostasis, and used the The presence of GOA in many type I chondrules, the highest Na analyses, e.g., of the glass in embayments addition of species such as SiO to their rims, and the shown in Fig. 10 to calculate DNa. abundance of forsteritic relict grains in type II Olivine partitioning experiments were made by chondrules all suggest that chondrule compositions Borisov et al. (2008), Kropf (2009), and Mathieu (2009). evolved from magnesian to ferroan, particularly in Chondrule interactions with nebular gas 1131

experiments (Yu and Hewins 1998; Yu et al. 2003) showed that rapid cooling was not adequate for reproducing chondrule volatile contents even at high total pressure. The above observations demonstrate that the ambient gas had high partial pressures of elements such as Na, Fe, and S, produced by evaporation from chondrules and accompanying fine dust, and (re-) condensation during chondrule formation would have been normal. Many calculated chondrule silicate melt composition glasses have close to the equilibrium compositions for gas enriched up to 1000· in lithophile elements (Ebel and Grossman 2000; Alexander 2004). Mathieu (2009) used experiments on Na solubility in )8 )5 CMAS liquids to determine PNa of 10 to 10 atm during chondrule formation. Hewins (1989) proposed formation of chondrules in a large dusty clump yielding Fig. 13. Type I and type II chondrules in Semarkona are high PNa on heating, an environment already seen as bound together and molded around each other in tight clusters necessary for lowering cooling rates (Hewins et al. 1981), resembling large compound chondrules. Many ordinary chondrites are ‘‘cluster chondrites’’ (Metzler 2011). and further justified by the recent work on Na in chondrule olivine (Alexander et al. 2008a; Borisov et al. 2008; Mathieu 2009). carbonaceous chondrites. The survival of Ti3+ in Nebular turbulence tends to concentrate chondrule- pyroxene and olivine in type II chondrules also suggests sized objects into clumps (Cuzzi et al. 1996) and reduced precursors (Simon et al. 2011). This is consistent chondrule cooling rates can be explained in shock wave with the more 16O-rich isotopic composition of olivine in models if chondrule formation involved clumps of many type I chondrules (Wasson 2000; Jones et al. 2004; chondrule-sized precursors (Desch and Connolly 2002). Kunihiro et al. 2005; Krot et al. 2006; Libourel and If big enough, these clumps are self-gravitating (Cuzzi Chaussidon 2011; Tenner et al. 2011b). Since the return et al. 2008). Partial pressures PSiO,Fe,K,Na,S were high, as of Genesis, we have learned that the Sun, and hence most chondrules contain metal or ferroan olivine as well early nebular gas, had low D17O (McKeegan et al. 2010), as troilite and Na-bearing glass and minerals. These and it has been proposed that primordial solids had partial pressures if generated from evaporating higher D17O (Krot et al. 2010b). In this interpretation, precursors require a high number density of melting there were lower dust–gas ratios for regions in which chondrules as well as large clumps to preserve the carbonaceous chondrite type I chondrules, or their evaporated gas in contact with chondrules. The time precursors, formed than where type II chondrules chondrules spent in free flight was not always long formed, and hence more dust–gas interaction. This is enough to ensure solidification before collision with consistent with lower partial pressures of O, Na, and S other chondrules or accumulation. However, the low during the formation of type I chondrules, and with number of compound chondrules observed suggests overlapping formation times of type I and type II lower number densities than the 104 m)3 estimated by chondrules (Amelin and Krot 2007; Kurahashi et al. Alexander et al. (2008). This paradox can be resolved for 2008; Villeneuve et al. 2009). many ordinary chondrites, because large clusters of Dusty olivine derived from type II chondrules occurs agglomerated chondrules are seen in polished sections, as relicts in some type I chondrules, which may therefore e.g., in Semarkona, as reported by Zanda (2004) and have formed from dustballs accumulated after the illustrated in Figs. 7b and 13. Such meteorites have been earliest chondrule-forming events. Statistics are lacking, called cluster chondrites (Metzler 2011). Thus volatile- but dusty relicts appear more common in ordinary rich chondrules were generated in very dense clumps, chondrites than in carbonaceous chondrites, suggesting and some solidified in clusters, being packed together, possibly more recycling in ordinary chondrites than in while some were solid and others still partly molten. carbonaceous chondrites, unless this simply results from Morris and Desch (2010) have proposed two ways to the absence of type II material in the environment in overcome the chondrule volatile problem. Vapor from which carbonaceous chondrites type I chondrules the densest core region of a precursor clump, in which all formed. solids are completely evaporated, can move outward, by Type II chondrules have chondritic Na (Hewins pressure-driven expansion. In the rest of the clump, 1991) and crystallize Na-bearing olivine. Evaporation melted chondrules cool in contact with this chondrule 1132 R. H. Hewins and B. Zanda vapor from the densest region. An alternative possibility of these embryos, whereas Dauphas and Pourmand (Morris and Desch 2010) is that chondrules are focused (2011) find isotopic evidence that Mars was formed very into the clumps, after peak heating, so that they cool in early, when nebular gas and dust were still present. the presence of very high pressures of chondrule vapor Morris et al. (2012) found that the embryos’ eccentric that can only arise from a region of higher chondrule orbits provide strong bow shocks that can process large concentration. The requisite PNa can be met by quantities of chondrules and cool them at appropriate evaporating a more reasonable chondrule concentration, rates. Passage of the chondrules through the upper possibly attainable by turbulent concentration. atmospheres of embryos with magma oceans may inhibit Following the success of nebular shock wave models evaporation. in reproducing chondrule cooling rates (e.g., Desch and Chondrites contain type I and type II chondrules, Connolly 2002), Fedkin et al. (2011, 2012) developed a both of which contain relict grains probably derived kinetic evaporation model and investigated a range of from the other. Thus, their formation times must have thermal histories for chondrule formation in gas shocks. overlapped, although type I chondrules in carbonaceous They tracked the changing compositions of olivine as it chondrites are more primitive in oxygen isotopes, as well crystallized and isotopic compositions during evaporation as more reduced. Both are found trapped and deformed and recondensation. They required enrichment by 550· in the same clusters (Zanda 2004; Metzler 2011) in solar in water, to make ferroan olivine in chondrules, and ordinary chondrites, where they have similar D17O (Kita 600· solar in dust, to retain Na, uncomfortably large et al. 2010), although their formation conditions differed. modifications to canonical conditions. The range of Fa This suggests turbulent mixing of hotter and colder contents of olivine in type II chondrules was reproduced, regions, which may be hard to explain with a very large- but large isotopic mass fractionations not observed in scale nebular shock, or mixing from domains with natural chondrules, particularly in Fe, were also different PH2O but the same isotopic composition produced. Isotopic heterogeneity could be suppressed (Connolly and Huss 2010; Kita et al. 2010). only with 100· shorter heating times coupled with dust In general, chondrule D17O values are explained by 4 )2 enrichments ‡6 · 10 and ⁄ or Ptot ‡ 10 bar. Fedkin and the equilibration of different amounts of solids and gas Grossman (2010) and Fedkin et al. (2011, 2012) argued of different isotopic compositions (Krot et al. 2010a; that such conditions could not be achieved in the disk Libourel and Chaussidon 2011). High PH2O is considered where the gas shocks occurred, so that chondrules were responsible for fayalite enrichment in chondrite olivine more likely to have formed in collisions of ice-bearing (Fedkin and Grossman 2006) and transport of 16O- planetesimals. depleted ice from outside the snowline is considered the Impacts cause rapid melting and vaporization, and cause of nebular gas of heavier isotopic composition produce clouds of silicate droplets in vapor with (Krot et al. 2006). Connolly and Huss (2010) combined enormous enrichments of volatilized rock, and in water if these ideas and proposed that type II chondrules in CR the bodies contained ice. A very good case has been made chondrites experienced both oxidation and depletion in that late-formed chondrules in CBb and some related 16O during melting, by isotopic exchange with this water- chondrites were formed in such an impact plume. There is enriched 16O-poor nebular gas. Type I chondrule olivines a very strong evaporation trend of refractory element have a wide range of D17O values (Libourel and enrichment in skeletal (blebby barred) olivine chondrules, Chaussidon 2011; Tenner et al. 2011a), with nearly and cryptocrystalline chondrules interpreted as condensed constant low olivine Fa contents indicating low PH2O; liquids are intimately connected with condensate metal type II chondrules have a more restricted range of D17O (Krot et al. 2007). It seems strange that normal values near and above TF, but a large range of olivine chondrules should be so different from CBb chondrules, if Fa contents. This suggests an abrupt increase in Fa both were formed by impact of planetesimals: different content of olivine in type II chondrules where isotopic target compositions and absence of ice in the CBb case compositions in the vicinity of TF were achieved (Russell might be an explanation. Differentiation or melting in the et al. 2010; Schrader et al. 2011; Tenner et al. 2011b); target may also be important (Asphaug et al. 2011). however, they may belong to reservoirs B and ⁄ or C of Morris et al. (2012) have investigated another Chaussidon et al. (2008). LL type II chondrules (Kita possible chondrule formation mechanism, melting in bow et al. 2010) have lighter oxygen isotopic compositions shocks around protoplanets or planetary embryos. (reservoir B) than type II chondrules in CC (reservoir C) Melting of nebular dust particles in bow shocks around such as Tagish Lake (Russell et al. 2010), CO chondrites asteroid-sized planetesimals is inefficient, but recent work (Tenner et al. 2011a), and some CR type II chondrules on the dynamical evolution of the disk emphasizes early (Connolly and Huss 2010). In addition, type I planetary embryos and perturbations of their orbits. chondrules with similar isotopic compositions (reservoir Walsh et al. (2011) show that Mars could be a survivor B) are present in LL chondrites. Thus, oxidation and Chondrule interactions with nebular gas 1133 enrichment in heavy isotopes may be decoupled, if, for case for S, which was present in ordinary chondrite example, SiO and H2O molecules equilibrate in the gas chondrule precursors, but not in those of carbonaceous (Javoy et al. 2012). The question remains whether the chondrite chondrules (with the possible exception of the necessary water pressures can be achieved on a large rare type II). Relict grains in incompletely melted scale, or whether local disruption of icy planetesimals is chondrules coming from AOA, GOA, or older generations required (Fedkin et al. 2012). of chondrules, and the variability of chondrule Some type I chondrules are zoned, with evidence of compositions, make it unlikely that chondrule precursors Si gain and Na gain, whereas type II are close to being in consisted simply of CI dust. equilibrium with an Na-rich gas. As both type I and type To a large extent, the variability of chondrule II chondrules entered clusters in the same ordinary properties may be ascribed to open system behavior, i.e., chondrite event, they may have been processed chemical and physical interaction between chondrules and separately in domains that mixed into the same clump ambient gas, including evaporation and condensation, for during cooling. Alternatively, both types of chondrules which there is evidence in both type I and type II may have been heated simultaneously with the type I chondrules. Textural sequences suggest evaporation, as chondrules acquiring elements evaporated from the type well as the low S content even of type II chondrules, but II chondrules. the extent of evaporation is difficult to evaluate due to the Carbonaceous chondrites are very different from superimposition of (re-) condensation upon cooling. ordinary chondrites, lacking their clusters of closely Non-lithophile elements such as Fe and S did not packed chondrules. Their chondrules were less processed dissolve back into the chondrule melt on recondensing and, as discussed above, had precursors devoid of S and formed opaque veneers. The compositions of these (Zanda 2004; Zanda et al. 2009). They accreted type I opaque veneers in carbonaceous chondrites and ordinary chondrules with abundant matrix and type II chondrules chondrites match those of their chondrule precursors are in the minority. Although type II chondrules must from which the elements evaporated: metal veneers have been formed under similar circumstances for decorate carbonaceous chondrite chondrules, while ordinary chondrites and carbonaceous chondrites, except ordinary chondrite chondrule veneers consist of sulfide for differences in fO2, those in carbonaceous chondrites with relict metal grains. The survival of some S within appear to have been removed from their dense clumps ordinary chondrite chondrules, and the presence of and transported, like refractory inclusions, to join a metallic Fe and forsteritic olivines side by side, suggest batch of type I chondrules, or rather several batches of evaporation to have been limited by the ambient gas type I chondrules from several reservoirs (Libourel and partial pressures. Chaussidon 2011). Carbonaceous chondrite type II Lithophile species show evidence of condensation chondrules may have been derived from a source region from the gas: Si, Na, Mn, and Fe as FeO, but, as these different from that of the type I chondrules as well as will dissolve into the chondrule melt, it is more difficult to from that of ordinary chondrite type II chondrules, decide whether these came from the evaporation of the based on their Fe–Mn trends (Fig. 6). More ice in this chondrules themselves or from that of adjoining dust. dust-rich source region would explain the higher fO2 The dominance of forsterite as relict material suggests an recorded in the type II chondrules of carbonaceous evolution from magnesian to more siliceous or ferroan chondrites. Type I and type II chondrules were mixed compositions with more processing. This evolution is without reheating in domains rich in dust, which became supported by oxygen isotope data and could indeed result carbonaceous chondrite matrix. from a net addition of material from the ambient gas. Type II chondrules can be explained by condensation of CONCLUSIONS FeO and MnO onto type I precursors under more oxidizing conditions for carbonaceous chondrites than Chondrules exhibit large variations in isotopic, for ordinary chondrites. chemical, mineralogical, and textural properties and The sequence of Na-rich olivine, Na-poor melt differ in a systematic way between ordinary chondrites inclusions, and Na-rich mesostases in type II chondrules and carbonaceous chondrites. Type I (magnesian) and in Semarkona records the whole history of evaporation type II (ferroan) chondrules, which require different followed by recondensation. This sequence could be formation conditions, are not distributed evenly between explained by the formation of ordinary chondrite the two groups: type II chondrules represent only a few chondrules in domains with large number densities and percent of carbonaceous chondrites, but most of high partial pressures of the rock-forming elements. ordinary chondrite chondrule material. These might be dense clumps in the disk heated by gas This variability of chondrule properties can, in part, shock waves, impact plumes formed by collisions of be ascribed to precursor effects. This is in particular the planetesimals, or the bow shocks of protoplanets. As 1134 R. H. Hewins and B. Zanda chondrule clusters in ordinary chondrites associate type I Bottke W. F., Nesvorny D., Grimm R. E., Morbidelli A., and and type II chondrules, it seems likely that these were O’Brien D. P. 2006. Iron meteorites as remnants of recycled simultaneously and reacted with the same gas planetesimals formed in the terrestrial planet region. Nature 439:821–824. reservoir. Carbonaceous chondrite type II chondrules Campbell A. J., Zanda B., Perron C., Meibom A., and Petaev were added late to batches of type I chondrules and M. I. 2005. Origin and thermal history of FeNi-metal in accreted with abundant matrix dust primitive chondrites. In Chondrites and the protoplanetary disk, vol. 341, edited by Krot A. N., Scott E. R. D., and Acknowledgments—We thank Harold C. Connolly, Jr. Reipurth B. San Francisco: Astronomical Society of the Pacific. pp. 407–431. for his support and for organizing the symposium Chaussidon M., Libourel G., and Krot A. 2008. Oxygen Chondrules: Their Role in Early Solar System History. isotopic constraints on the origin of magnesian chondrules We thank B. Devouard and A. N. Krot for images of and on the gaseous reservoirs in the early Solar System. chondrules. The manuscript was improved by Geochimica et Cosmochimica Acta 72:1924–1938. constructive reviews from J. S. Boesenberg and H. C. Cohen B. A. and Hewins R. H. 2004. An experimental study of the formation of metallic iron in chondrules. Geochimica et Connolly, Jr. It was written with financial support Cosmochimica Acta 68:1677–1689. provided by the Program National de Plane´tologie and Cohen B. A., Hewins R. H., and Alexander C. M. O’D. 2004. ANR no. 07-BLAN-0130-04 ‘‘MIME,’’ B. Zanda. The formation of chondrules by open-system melting of nebular condensates. Geochimica et Cosmochimica Acta Editorial Handling—Dr. Harold Connolly 68:1661–1675. Connelly J. N., Bizzarro M., Ivanova M., and Krot A. N. 2011. Towards a new absolute chronology for the early solar REFERENCES system (abstract #9056). Workshop on Formation of the First Solids in the Solar System. Houston: Lunar and Alexander C. M. O’D. 1996. Recycling and volatile loss in Planetary Institute. chondrule formation. In Chondrules and the protoplanetary Connolly H. C., Jr. and Huss G. R. 2010. Compositional disk, edited by Hewins R. H., Jones R. H., and Scott E. R. evolution of the protoplanetary disk: Oxygen isotopes of D. Cambridge, UK: Cambridge University Press. pp. 233– type-II chondrules from CR2 chondrites. Geochimica et 241. Cosmochimica Acta 74:2473–2483. Alexander C. M. O’D. 2004. Chemical equilibrium and kinetic Connolly H. C., Jr., Hewins R. H., Ash R. D., Zanda B., constraints for chondrule and CAI formation conditions. Lofgren G. E., and Bourot-Denise M. 1994. Carbon and Geochimica et Cosmochimica Acta 68:3943–3969. the formation of reduced chondrules: An experimental Alexander C. M. O’D., Grossman J. N., Wang J., Zanda B., investigation. Nature 371:136–139. Bourot-Denise M., and Hewins R. H. 2000. The lack of Connolly H. C., Jr., Huss G. R., and Wasserburg G. J. 2001. potassium isotopic fractionation in Bishunpur chondrules. On the formation of Fe–Ni metal in Renazzo-like Meteoritics & Planetary Science 35:859–868. carbonaceous chondrites. Geochimica et Cosmochimica Acta Alexander C. M. O’D., Grossman J. N., Ebel D. S., and Ciesla 65:4567–4588. F. J. 2008a. The formation conditions of chondrules and Cuzzi J. N. and Alexander C. M. O’D. 2006. Chondrule chondrites. Science 320:1617–1619. formation in particle-rich nebular regions at least hundreds Alexander C. M. O’D., Ebel D. S., Ciesla F., and Grossman J. of kilometres across. Nature 441:483–485. N. 2008b. Reassessing the conditions of chondrule Cuzzi J. N., Dobrovolskis A. R., and Hogan R. C. 1996. formation (abstract #2440). 39th Lunar and Planetary Turbulence, chondrules, and planetesimals. In Chondrules Science Conference. CD-ROM. and the protoplanetary disk, edited by Hewins R. H., Jones Amelin Y. and Krot A. N. 2007. Pb isotopic age of the Allende R. H., and Scott E. R. D. Cambridge, UK: Cambridge chondrules. Meteoritics & Planetary Science 42:1321–1335. University Press. pp. 35–43. Amelin Y., Krot A. N., Hutcheon I. D., and Ulyanov A. A. Cuzzi J. N., Hogan R. C., and Shariff K. 2008. Toward 2002. Lead isotopic ages of chondrules and calcium– planetesimals: Dense chondrule clumps in the protoplanetary aluminum-rich inclusions. Science 297:1678–1683. nebula. The Astrophysical Journal 687:1432–1447. Asphaug E., Agnor C. B., and Williams Q. 2006. Hit-and-run Danyushevsky L. V. 2001. The effect of small amounts of H2O planetary collisions. Nature 439:155–160. on crystallization of mid-ocean ridge and backarc basin Asphaug E., Martin J., and Movshovitz N. 2011. Chondrule magmas. Journal of Volcanology and Geothermal Research formation by partial accretion of planetesimals (abstract 110:265–280. #1647). 42nd Lunar and Planetary Science Conference. Danyushevsky L. V. and Plechov P. 2011. Petrolog3: Integrated CD-ROM. software for modeling crystallization processes. Berlin J., Jones R. H., and Brearley A. J. 2011. Fe-Mn Geochemistry Geophysics Geosystems 12:Q07021, doi:10.1029 ⁄ systematics of type IIA chondrules in unequilibrated CO, 2011GC003516. CR, and ordinary chondrites. Meteoritics & Planetary Dauphas N. and Pourmand A. 2011. Hf-W-Th evidence for Science 46:513–533. rapid growth of Mars and its status as a planetary embryo. Borisov A., Pack A., Kropf A., and Palme H. 2008. Nature 473:489–492. Partitioning of sodium between olivine and melt: An Davis A. M., Alexander C. M. O’D., Nagahara H., and experimental study with application to the formation of Richter F. M. 2005. Evaporation and condensation during meteoritic Na-rich chondrule glass and refractory CAI and chondrule formation. In Chondrites and the forsterites. Geochimica et Cosmochimica Acta 72:5558–5573. protoplanetary disk, vol. 341, edited by Krot A. N., Scott Chondrule interactions with nebular gas 1135

E. R. D., and Reipurth B. San Francisco: Astronomical Hewins R. H. 1999. Relict pyroxene—Constraint on chondrule Society of the Pacific. pp. 432–455. melting? (abstract #1678). 30th Lunar and Planetary Desch S. J. and Connolly H. C., Jr. 2002. A model for the Science Conference. CD-ROM. thermal processing of particles in solar nebula shocks: Hewins R. H. and Fox G. E. 2004. Chondrule textures and Application to cooling rates of chondrules. Meteoritics & precursor grain size: An experimental study. Geochimica et Planetary Science 37:183–207. Cosmochimica Acta 68:917–926. Dodd R. T. 1971. Dark-zoned chondrules. Chemie der Erde Hewins R. H., Klein H. C., and Fasano B. V. 1981. Conditions 30:59–69. of formation of pyroxene excentroradial chondrules. Ebel D. S. and Grossman L. 2000. Condensation in dust- Proceedings, 12th Lunar and Planetary Science Conference. enriched systems. Geochimica et Cosmochimica Acta pp. 1123–1133. 64:339–366. Hewins R. H., Yu Y., Zanda B., and Bourot-Denise M. 1997. Faure F. and Schiano P. 2005. Experimental investigation of Do nebular fractionations, evaporative losses, or both equilibration conditions during forsterite growth and melt influence chondrule compositions? Antarctic Meteorite inclusion formation. Earth and Planetary Science Letters Research 10:294–317. 236:882–898. Hewins R. H., Connolly H. C., Jr., Lofgren G. E., and Fedkin A. V. and Grossman L. 2006. The fayalite content of Libourel G. 2005. Experimental constraints on chondrule chondritic olivine: Obstacle to understanding the formation. In Chondrites and the protoplanetary disk, vol. condensation of rocky material. In Meteorites and the early 341, edited by Krot A. N., Scott E. R. D., and Reipurth B. solar system II, edited by Lauretta D. S. and McSween San Francisco: Astronomical Society of the Pacific H. Y., Jr. Tucson, Arizona: The University of Arizona Conference. pp. 286–317. Press. pp. 279–294. Hewins R. H., Zanda B., and Bourot-Denise M. 2011. The Fedkin A. V. and Grossman L. 2010 Condensation of the high- formation of Type II chondrules in CM chondrites: The FeO silicates in primitive chondrites: Still a problem view from Paris (abstract #1914). 42nd Lunar and (abstract #1448). 41st Lunar and Planetary Science Planetary Science Conference. CD-ROM. Conference. CD-ROM. Hewins R. H., Zanda B., and Bendersky C. 2012. Evaporation Fedkin A. V., Ciesla F. J., and Grossman L. 2008. Shock wave and recondensation of sodium in Semarkona Type II models: Dependence of thermal history and Type II chondrules. Geochimica et Cosmochimica Acta 78:1–17. chondrule composition on water and dust enrichment Hezel D. C. and Palme H. 2007. The conditions of chondrule (abstract #1834). 39th Lunar and Planetary Science formation, Part I: Closed system. Geochimica et conference. CD-ROM. Cosmochimica Acta 71:4092–4107. Fedkin A. V., Grossman L., Ciesla F. J., and Simon S. B. 2011. Humayun M., Campbell A. J., Zanda B., and Bourot-Denise Mineralogical and isotopic effects of shock wave thermal M. 2002. Formation of Renazzo chondrule metal inferred histories on chondrule precursors (abstract #1533). 42nd from siderophile elements (abstract #1965). 32nd Lunar and Lunar and Planetary Science Conference. CD-ROM. Planetary Science Conference. CD-ROM. Fedkin A. V., Grossman L., Ciesla F. J., and Simon S. B. 2012. Humayun M., Connolly H. C., Jr., Rubin A. E., and Mineralogical and isotopic constraints on chondrule Wasson J. T. 2010. Elemental distribution in metal from formation from shock wave thermal histories. Geochimica the CR chondrites Acfer 059 and PCA 91082 (abstract et Cosmochimica Acta 87:81–116. #1840). 41st Lunar and Planetary Science Conference. Fredricksson K. 1969. The Sharps chondrite: A new evidence CD-ROM. on the origin of chondrules and chondrites. In Meteorite Jarosewich E. 1990. Chemical analyses of meteorites—A research, edited by Millman P. M. Dordrecht: Reidel. pp. compilation of stony and iron meteorite analyses. 155–165. Meteoritics 25:323–337. Georges P., Libourel G., and Deloule E. 2000. Experimental Javoy M., Balan E., Me´heut M., Blanchard M., and Lazzer M. constraints on alkali condensation in chondrule formation. 2012. First-principles investigation of equilibrium isotopic Meteoritics & Planetary Science 35:1183–1188. fractionation of O- and Si-isotopes between refractory Gounelle M., Young E. D., Shahar A., Tonui E., and Kearsley solids and gases in the solar nebula. Earth and Planetary A. 2007. Magnesium isotopic constraints on the origin of Science Letters 219:118–127. CBb chondrites. Earth and Planetary Science Letters Jones R. H. 1990. Petrology and mineralogy of Type II, 256:521–533. FeO-rich chondrules in Semarkona LL3.0: Origin by Grossman J. N. and Wasson J. T. 1982. Evidence for primitive closed-system fractional crystallization, with evidence for nebular components in chondrules from the chainpur supercooling. Geochimica et Cosmochimica Acta 54: chondrite. Geochimica et Cosmochimica Acta 46:1081–1099. 1785–1802. Halliday A. N. and Kleine T. 2006. Meteorites and the timing, Jones R. H. 1994. Petrology of FeO-poor, porphyritic pyroxene mechanisms and conditions of terrestrial planet accretion chondrules in the Semarkona chondrite. Geochimica et and early differentiation. In Meteorites and the early solar Cosmochimica Acta 158:5325–5340. system II, edited by Lauretta D., Leshin L., and McSween Jones R. H. 1996a. FeO-rich porphyritic pyroxene chondrules H. Tucson, Arizona: The University of Arizona Press. pp. in unequilibrated ordinary chondrites. Geochimica et 775–801. Cosmochimica Acta 60:3115–3138. Hewins R. H. 1989. The evolution of chondrules. Proceedings Jones R. H. 1996b. Relict grains in chondrules: Evidence for of the NIPR Symposium on Antarctic Meteorites 2:202–222. chondrule recycling. In Chondrules and the protoplanetary Hewins R. H. 1991. Retention of sodium during chondrule disk,editedbyHewinsR.H.,JonesR.H.,andScottE.R.D. melting. Geochimica et Cosmochimica Acta 55:935–942. Cambridge, UK: Cambridge University Press. pp. 163–172. Hewins R. H. 1997. Chondrules. Annual Reviews of Earth and Jones R. H. and Scott E. R. D. 1989. Petrology and thermal Planetary Sciences 25:61–83. history of type IA chondrules in the Semarkona LL3.0 1136 R. H. Hewins and B. Zanda

chondrite. Proceedings, 19th Lunar and Planetary Science mechanisms and multiple chondrule generations. Chemie Conference. pp. 523–536. der Erde 67:283–300. Jones R. H., Leshin L. A., Guan Y., Sharp Z. D., Durakiewicz Krot A. N., Nagashima K., Yoshitake M., and Yurimoto H. T., and Schilk A. J. 2004. Oxygen isotope heterogeneity in 2010a. Oxygen isotopic compositions of chondrules from chondrules from the Mokoia CV3 carbonaceous chondrite. the metal-rich chondrites Isheyevo CH ⁄ CBb, MAC 02675 Geochimica et Cosmochimica Acta 68:3423–3438. CBb and QUE 94627 CBb. Geochimica et Cosmochimica Jones R. H., Grossman J., and Rubin A. E. 2005. Chemical, Acta 74:2190–2211. mineralogical and isotopic properties of chondrules: Clues Krot A. N., Nagashima K., Ciesla F. J., Meyer B. S., Hutcheon to their origins. In Chondrites and the protoplanetary disk, I. D., Davis A. M., Huss G. R., and Scott E. R. D. 2010b. vol. 341, edited by Krot A. N, Scott E. R. D., and Reipurth Oxygen isotopic composition of the Sun and mean oxygen B. San Francisco: Astronomical Society of the Pacific. pp. isotopic composition of the protosolar silicate dust: 251–285. Evidence from refractory inclusions. The Astrophysical Kita N., Nagahara H., Togashi S., and Morishita Y. 2000. A Journal 713:1159–1166. short duration of chondrule formation in the solar nebula: Kunihiro T., Rubin A. E., and Wasson J. T. 2005. Oxygen- Evidence from 26Al in Semarkona ferromagnesian isotopic compositions of low-FeO relicts in high-FeO host chondrules. Geochimica et Cosmochimica Acta 74:6610–6635. chondrules in Acfer 094, a type-3.0 carbonaceous chondrite Kita N., Huss G. R., Tachibana S., Amelin Y., Nyquist L. E., closely related to CM. Geochimica et Cosmochimica Acta and Hutcheon I. D. 2005. Constraints on the origin of 69:3831–3840. chondrules and CAIs from short-lived and long-lived Kurahashi E., Kita N. T., Nagahara H., and Morishita Y. radionuclides. In Chondrites and the protoplanetary disk, 2008. 26Al–26Mg systematics of chondrules in a primitive vol. 341, edited by Krot A. N., Scott E. R. D., and CO chondrite. Geochimica et Cosmochimica Acta 72: Reipurth B. San Francisco: Astronomical Society of the 3865–3882. Pacific. pp. 286–317. Lauretta D. S., Lodders K., and Fegley B., Jr. 1997. Kita N., Nagahara H., Tachibana S., Tomomura S., Spicuzza Experimental simulations of sulfide formation in the solar M. J., Fournelle J. H., and Valley J. W. 2010. High nebula. Science 277:358–360. precision SIMS oxygen three isotope study of chondrules in Lee M. S., Rubin A. E., and Wasson J. T. 1992. Origin of LL3 chondrites: Role of ambient gas during chondrule metallic Fe-Ni in Renazzo and related chondrites. formation. Geochimica et Cosmochimica Acta 68:3423–3438. Geochimica et Cosmochimica Acta 56:2521–2533. Kleine T., Mezger K., Palme H., Scherer E., and Mu¨ nker C. Lewis R. D., Lofgren G. E., Franzen H. F., and Windom K. E. 2005. Early core formation in asteroids and late accretion 1993. The effect of Na vapor on the Na content of of chondrite parent bodies: Evidence from 182Hf-182Win chondrules. Meteoritics 28:622–628. CAIs, metal-rich chondrites, and iron meteorites. Libourel G. 1999. Systematics of calcium partitioning between Geochimica et Cosmochimica Acta 69:5805–5818. olivine and silicate melt: Implications for melt structure and Kleine T., Touboul M., Bourdon B., Nimmo F., Mezger K., calcium content of magmatic systems. Contributions in Palme H., Yin Q. Z., Jacobsen S. B., and Halliday A. N. Mineralogy and Petrology 136:63–80. 2009. Hf-W chronology of the accretion and early evolution Libourel G. and Chaussidon M. 2011. Oxygen isotopic of asteroids and terrestrial planets. Geochimica et constraints on the origin of Mg-rich olivines from Cosmochimica Acta 73:5150–5188. chondritic meteorites. Earth and Planetary Science Letters Kropf A. 2009. Alkalien in chondren—Offenes oder 301:9–21. geschlossenes system? Dissertation Dr. rer. nat., Georg- Libourel G. and Krot A. N. 2007. Evidence for the presence of August-Universita¨ t, Go¨ ttingen, 129 p. planetesimal material among the precursors of magnesian Krot A. N., Libourel G., Goodrich C. A., and Petaev M. I. chondrules of nebular origin. Earth and Planetary Science 2004. Silica-rich igneous rims around magnesian chondrules Letters 254:1–8. in CR carbonaceous chondrites: Evidence for fractional Libourel G., Krot A. N., and Tissandier L. 2006. Role of gas– condensation during chondrule formation. Meteoritics & melt interaction during chondrule formation. Earth and Planetary Science 39:1931–1955. Planetary Science Letters 251:232–240. Krot A. N., Amelin Y., Cassen P., and Meibom A. 2005a. Lofgren G. E. 1996. A dynamic crystallization model for Young chondrules in CB chondrites formed by a giant chondrule melts. In Chondrules and the protoplanetary impact in the early Solar System. Nature 436:989–992. disk, edited by Hewins R. H., Jones R. H., and Scott E. Krot A. N., McKeegan K. D., Huss G. R., Liffman K., R. D. Cambridge, UK: Cambridge University Press, pp. Sahijpal S., Hutcheon I. D., Srinivasan G., Bischoff A., and 187–196. Keil K. 2005b. Aluminum-magnesium and oxygen isotope MacPherson G. J. and Huss G. R. 2005. Petrogenesis of Al-rich study of relict Ca-Al-rich inclusions in chondrules. The chondrules: Evidence from bulk compositions and phase Astrophysical Journal 629:1227–1237. equilibria. Geochimica et Cosmochimica Acta 69:3099–3127. Krot A. N., Yurimoto H., McKeegan K. D., Leshin L., Mathieu R. 2009. Solubilite´du sodium dans les silicates fondus. Chaussidon M., Libourel G., Yoshitake M., Huss G. R., Ph.D. thesis, INPL-CRPG, Nancy, France: 393 pp. Guan Y., and Zanda B. 2006. Oxygen isotopic Matsunami S., Ninagawa K., Nishimura S., Kubono N., compositions of chondrules: Implications for evolution of Yamamoto I., Kohata M., Wada T., Yamashita Y., Lu J., oxygen isotopic reservoirs in the inner solar nebula. Chemie Sears D. W. G., and Nishimura H. 1993. der Erde 66:249–276. Thermoluminescence and compositional zoning in the Krot A. N., Ivanova M. A., and Ulyanov A. A. 2007. mesostasis of a Semarkona group A1 chondrule and new Chondrules in the CB ⁄ CH-like carbonaceous chondrite insights into the chondrule-forming process. Geochimica et Isheyevo: Evidence for various chondrule-forming Cosmochimica Acta 57:2101–2110. Chondrule interactions with nebular gas 1137

McKeegan K. D., Kallio A., Heber V. S., Jarzebinski G., Mao Simon S. B., Sutton S. R., and Grossman L. 2011. The growing P., Coath C., Kunihiro T., Wiens R. C., Judith A., and inventory of Ti3+-bearing objects from the solar nebula Burnett D. S. 2010. The oxygen isotopic composition of the (abstract #9074). LPI Workshop on Formation of the First Sun (abstract #V31B-2316). American Geophysical Union, Solids in the Solar System, Poipu Beach, Hawai’i. Fall Meeting. Tenner T. J., Ushikubo T., Kurahashi E., Kita N. T., and McSween H. Y., Jr. 1977a. Chemical and petrographic Nagahara H. 2011a. Oxygen isotopic measurements of constraints on the origin of chondrules and inclusions in phenocrysts in chondrules from the primitive carbonaceous carbonaceous chondrites. Geochimica et Cosmochimica Acta chondrite Yamato 81020: Evidence for two distinct oxygen 41:1843. isotope reservoir (abstract #1426). 42nd Lunar and McSween H. Y., Jr. 1977b. Report. Cambridge, Massachusetts: Planetary Science Conference. CD-ROM. Harvard ⁄ Smithsonian Center for Astrophysics. 19 p. Tenner T. J., Nakashima D., Ushikubo T., Kita N. T., and Metzler K. 2011. Chondrite accretion within hours to a few Weisberg M. K. 2011b. Oxygen isotope ratios in chondrules days after chondrule formation? Textural evidence from from primitive CR chondrite MET 00426: A correlation UOCs (abstract #9111). LPI Workshop on Formation of with chondrule Mg# (abstract #5366). 74th Annual the First Solids in the Solar System, Poipu Beach, Hawai’i. Meteoritical Society Meeting. Miyamoto M., Mikouchi T., and Jones R H. 2009. Cooling Tissandier L., Libourel G., and Robert F. 2002. Gas–melt rates of porphyritic olivine chondrules in the Semarkona interactions and their bearing on chondrule formation. LL3.00 ordinary chondrite: A model for diffusional Meteoritics & Planetary Science 37:1377–1389. equilibration of olivine during fractional crystallization. Tronche E. J., Hewins R. H., and MacPherson G. J. 2007. Meteoritics & Planetary Science 44:521–530. Formation conditions of aluminum-rich chondrules. Morris M. A. and Desch S. J. 2010. Thermal histories of Geochimica et Cosmochimica Acta 70:3361–3381. chondrules in solar nebula shocks. The Astrophysical Tschermak G. 1885. Die mikroskopische Beschaffenheit der Journal 722: 1474–1494. Meteoriten. Sitzungsb. Akad. Wiss. Wien 71,661 trans by J. Morris M. A., Boley A. C., Desch S. J., and Athanassiadou T. A. and E. M. Wood, 1964, Smithsonian Contributions to 2012. Chondrule formation in bow shocks of eccentric Astrophysics, 4:139. planetary embryos. The Astrophysical Journal 752(1): 27. Villeneuve J. 2010. Formation des chondres: Pre´curseurs et Nettles J. W., Lofgren G. E., and McSween H. Y., Jr. 2002. chronologie. Ph.D. thesis, INPL-CRPG, Nancy, France. Recycled ‘‘chondroids’’ in LEW 86018: A petrographic Villeneuve J., Chaussidon M., and Libourel G. 2009. study of chondrule precursors (abstract #1752). 33rd Lunar Homogeneous distribution of 26Al in the Solar System from and Planetary Science Conference. CD-ROM. the Mg isotopic composition of chondrules. Science Radomsky P. M. and Hewins R. H. 1990. Formation conditions 325:985–988. of pyroxene-olivine and magnesian olivine chondrules. Walsh K. J., Morbidelli A., Raymond S. N., O’Brien D. P., and Geochimica et Cosmochimica Acta 54:3475–3490. Mandell A. M. 2011. A low mass for Mars from Jupiter’s Russell S. D. J., Longstaffe F. J., King P. L., and Larson T. E. early gas-driven migration. Nature 475:206–209. 2010. The oxygen-isotope composition of chondrules and Wasson J. T. 2000. Oxygen-isotopic evolution of the solar isolated forsterite and olivine grains from the Tagish Lake nebula. Reviews in Geophysics 38:491–512. carbonaceous chondrite. Geochimica et Cosmochimica Acta Wasson J. T. and Rubin A. E. 2010. Metal in CR chondrites. 74:2484–2499. Geochimica et Cosmochimica Acta 74:2212–2230. Ruzicka A., Hiyagon H., Hutson M., and Floss C. 2007. Relict Weisberg M. K. and Prinz M. 1996. Agglomeratic chondrules, olivine, chondrule recycling, and the evolution of nebular chondrule precursors and incomplete melting. In oxygen reservoirs. Earth and Planetary Science Letters Chondrules and the protoplanetary disk, edited by Hewins R. 257:274–289. H., Jones R. H., and Scott E. R. D. Cambridge, UK: Sahagian D. L. and Hewins R.H. 1992. The size of chondrule- Cambridge University Press, pp. 119–127. forming events. Proceedings, 23rd Lunar and Planetary Whattam S. A. and Hewins R. H. 2009. Granoblastic olivine Science Conference. pp. 1197–1198. aggregates as precursors of Type I chondrules: An experimental Schrader D. L., Connolly H. C., Jr., Lauretta D. S., Nagashima test. Geochimica etCosmochimica Acta73:5460–5482. K., and Huss G. R. 2011. Relationship between FeO Wick M. J. 2010. Formation conditions of plagioclase-bearing content and D17O In chondrules from CR chondrites: Type I chondrules in CO chondrites: A study of natural Linking oxygen fugacity and O-isotope evolution (abstract samples and experimental analogs. M.S. thesis, University #5343). 74th Annual Meteoritical Society Meeting. of New Mexico, Albuquerque. Scott E. R. D. and Krot A. N. 2005. Chondrites and their Wick M. J. and Jones R. H. Forthcoming. Formation conditions components. In Meteorites, comets and planets, edited by of plagioclase-bearing Type I chondrules in CO chondrites: Davis A. M. Treatise on geochemistry, vol. 1, edited by A study of natural samples and experimental analogs. Holland H. D. and Turekian K. K. Oxford: Elsevier- Geochimica et Cosmochimica Acta. submitted. Pergamon. pp. 143–200. Wood J. A. 1996. Unresolved issues in the formation of chondrules Scott E. R. D. and Taylor G. J. 1983. Chondrules and other and chondrites. In Chondrules and the protoplanetary disk, components in C, O, and E chondrites: Similarities in their edited by Hewins R. H., Jones R. H., and Scott E. R. D. properties and origins. Proceedings, 14th Lunar and Cambridge,UK:CambridgeUniversityPress.pp.55–69. Planetary Science Conference. pp. B275–286. Wood J. A. and Hashimoto A. 1993. Mineral equilibrium in Sears D. W. G., Huang S., and Benoit P. H. 1996. Open system fractionated nebular systems. Geochimica et Cosmochimica behaviour during chondrule formation. In Chondrules and Acta 57:2377–2388. the protoplanetary disk, edited by Hewins R. H., Jones R. Yu Y. and Hewins R. H. 1998. Transient heating and chondrule H., and Scott E. R. D. Cambridge, UK: Cambridge formation—Evidence from Na loss in flash heating simulation University Press. pp. 221–231. experiments.Geochimica et Cosmochimica Acta62:159–172. 1138 R. H. Hewins and B. Zanda

Yu Y., Hewins R. H., Alexander C. M. O’D., and Wang J. Zanda B., Bourot-Denise M., Hewins R. H., Cohen B. A., 2003. Experimental study of evaporation and isotopic mass Delaney J. S., Humayun M., and Campbell A. J. 2002. fractionation of potassium in silicate melts. Geochimica et Accretion textures, iron evaporation and re-condensation in Cosmochimica Acta 67:773–786. Renazzo chondrules (abstract #1852). 33rd Lunar and Yurimoto H. and Wasson J. T. 2002. Extremely rapid cooling Planetary Science Conference. CD-ROM. of a carbonaceous chondrite chondrule containing very Zanda B., Hewins R. H., Bourot-Denise M., Bland P. A., and 16O-rich olivine and a 26Mg excess. Geochimica et Albare` de F. 2006. Formation of solar nebula reservoirs by Cosmochimica Acta 66:4355–4363. mixing chondritic components. Earth and Planetary Science Zanda B. 2004. Chondrules. Earth and Planetary Science Letters 248:650–660. Letters 224:129. Zanda B., Le Guillou C., and Hewins R. H. 2009. The Zanda B., Bourot-Denise M., and Hewins R. H. 1995. relationship between chondrules and matrix in chon- Condensate sulfide and its metamorphic transformations in drites (abstract #5280). Meteoritics & Planetary Science 43: primitive chondrites. Meteoritics 30:605. A225.