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Bulk chemical compositions of Al-rich objects from Rumuruti (R) chondrites:Implications for their origin

Surya Snata Rout a,n, Klaus Keil b, Addi Bischoff a

a Institut fur Planetologie, Westfalische Wilhelms-Universitat Munster, Wilhelm-Klemm-Strasse 10, 48149 Munster, Germanyb Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA

a r t i c l e i n f o

Article history:

Received 1 September 2009

Accepted 29 October 2009

Keywords:

R chondrites

Calcium–aluminum-rich inclusions (CAIs)

Fassaite-bearing spherules

Al-rich chondrules

Carbonaceous chondrites

a b s t r a c t

R chondrites are a distinct group of chondritic meteorites with unique mineralogical and chemical

compositions. They contain various types of Al-rich objects [Ca,Al-rich inclusions (CAIs), Al-rich

chondrules and fragments], whose mineralogical compositions and classifications were previously

determined by Rout and Bischoff (2008). Here, we report on the bulk compositions of 126 such Al-rich

objects determined by broad-beam electron probe microanalysis.

Most of the CAIs, except a few, are significantly altered by complex nebular and/or parent body

processes and the determination of their pristine composition is difficult. We found that the simple

concentric spinel-rich inclusions have high Al2O3 (21–72 wt%) correlated with their high modal spinel.

The subgroup of simple concentric spinel-rich CAIs have a high Al2O3 (21–57 wt%) and also sometimes

high FeO (up to 36 wt%), due to a high hercynitic component in the spinel. One simple concentric

spinel- and hibonite-rich CAI H030/L, identified as a HAL-type CAI by isotopic studies reported

elsewhere, has a highly refractory composition (Al2O3�72 wt%). Most of the simple concentric spinel-

and fassaite-rich CAIs have consistently high CaO (�2.5–17 wt%) compared to other simple concentric

spinel-rich inclusions group, where only some inclusions have high CaO (up to 15 wt%). Simple

concentric spinel- and Na,Al-alteration product-rich CAIs are heavily altered and have high Na2O (up to

�12.5 wt%).

The three analyzed fassaite-rich spherules have high CaO and Al2O3, and complex spinel- and

fassaite-rich CAIs have high CaO (up to 23 wt%) and SiO2 (up to 41 wt%). Most of the complex spinel-

and plagioclase-rich CAIs are altered and contain high amounts of secondary oligoclase. However, a few

are less affected by secondary alteration and these are characterized by relatively high CaO (up to

24 wt%) and Al2O3 (18–33 wt%); complex spinel and Na,Al-alteration product-rich CAIs are similar to

the concentric spinel- and Na,Al-alteration product-rich CAIs. Due to Fe- and alkali-metasomatism, the

vast majority of the inclusions in this subgroup were heavily altered, either in a nebular or parent body

environment. As a result of this alteration, they contain high FeO and Na2O+K2O+Cl.

Almost all inclusions have a Ca/Al-ratio below the solar ratio. This suggests that significant Ca/Al

fractionation occurred during the formation of most CAIs, most probably due to disequilibrium

condensation of spinel prior to melilite. However, a distillation process cannot be ruled out for some

CAIs in producing the spinel enrichment. Some porous and fine grained CAIs may have been produced

by agglomeration of refractory dust rich in spinel and fassaite. The HAL-type CAI, H030/L, most likely

formed by distillation, similar to most of the HAL-type inclusions. Phase equilibrium analysis, in the

CMAS system, shows that the fassaite-bearing spherules most likely formed by metastable crystal-

lization and disequilibrium processes. Al-rich chondrules are characterized by 410 wt% Al2O3, and

most of these also have high FeO and Na2O. Considering their bulk compositions, their precursors seem

to have been a mixture of a ferromagnesian chondrule component rich in olivine and an anorthite–

spinel–pyroxene–nepheline-rich CAI component. The mineral assemblages of some of the less altered

Al-rich chondrules conform to those predicted by phase equilibrium studies.

& 2009 Elsevier GmbH. All rights reserved.

Introduction

Calcium–Aluminum-rich Inclusions (CAIs) and chondrules,which constitute major components in chondritic meteorites(e.g., MacPherson et al., 1988; MacPherson, 2003), represent the

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doi:10.1016/j.chemer.2009.10.002

n Corresponding author. Tel.: +49 251 8336377; fax: +49 251 8336301.

E-mail address: suryarout@uni-muenster.de (S.S. Rout).

Chemie der Erde 70 (2010) 35–53

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earliest solids that formed in the solar nebula by hightemperature processes (e.g., Grossman, 1972; Amelin et al.,2002). Their study provides significant insight into the physicaland chemical conditions in the Solar Nebula and the early solarsystem.

The Rumuruti (R) chondrites, formerly called the ‘‘CarlisleLakes-type’’ chondrites (Binns and Pooley, 1979; Rubin andKallemeyn, 1989; Weisberg et al., 1991), are named after theRumuruti meteorite, the first, and so far only R chondrite fall; allother R chondrites are finds from either hot deserts or Antarctica(Schulze et al., 1994). They are a well-characterized chondritegroup distinct from carbonaceous, ordinary and enstatite chon-drites (e.g., Schulze et al., 1994; Bischoff et al., 1994; Rubin andKallemeyn, 1994; Kallemeyn et al., 1996). They are uniquebecause of their high oxidation state, reflected by their high FeOcontents in olivine (�38–40 mol.% Fa), low metallic Fe,Nicontents, abundance of sulphides, high modal abundance ofolivine, and high D17O of �2.7% (Rumuruti proper has thehighest D17O of �2.88%) (Schulze et al., 1994; Bischoff et al.,1994; Jackel et al., 1996; Kallemeyn et al., 1996). About half of theR chondrites are regolith breccias, showing the typical light/darkstructure and having solar wind-implanted rare gases (Weber andSchultz, 1995; Bischoff and Schultz, 2004; Bischoff et al., 2006).Most of the R-chondrites are mixtures of unequilibrated, type 3fragments (Bischoff et al., 1998; Bischoff, 2000) and clastsmetamorphosed to various degrees, and should be considered asR3-5 or R3-6 breccias (e.g., Bischoff et al., 1994; Schulze et al.,1994; Kallemeyn et al., 1996). Unequilibrated chondritic compo-nents have been reported from many R chondrites (e.g., Weisberget al., 1991; Schulze et al., 1994; Bischoff et al., 1994; Rubin andKallemeyn, 1994). Jackel et al. (1996) reported several type 3clasts in Dar al Gani 013 having beautifully developed chondritictextures.

Here, we present bulk chemical analyses of the CAIsand Al-rich chondrules whose mineralogy and petrologywe previously studied (Rout and Bischoff, 2008). Examples oftypical CAIs and Al-rich objects are shown in Figs. 1 and 2. Thesedata contribute to a better understanding of the origin of theseobjects and their relationship to those in other chondriticmeteorites.

Samples and analytical procedures

Backscattered electron images shown in Figs. 1 and 2 wereobtained with a JEOL 840 A scanning electron microscope. Thebulk compositions of 126 CAIs and Al-rich chondrules in 20 Rchondrites (Table 1) were determined in polished thin and thicksections with a defocused electron beam of varying diameterusing a JEOL 8900 electron microprobe operated at 15 kV and aprobe current of 15 nA. The defocused beam diameter was variedfrom 10 to 50 mm depending upon the size of the CAI/Al-richchondrule and multiple spots were analyzed within a singleinclusion. Finally, a weighted mean of the analyses was calculatedto estimate the bulk composition. The position of the beam wascarefully selected to cover the whole area of the inclusion and toavoid any overlap with cracks and holes. However, this could notbe done for all inclusions. Many of the CAIs, which have highporosity throughout the entire inclusion, give low oxide totals,and these data are renormalized to 100 wt%. This may causeerrors in elemental ratios due to the different activation volumeas compared to the volume assumed in the correction scheme anddue to the variable incidence angle of the beam on the sample.Additional errors due to sectioning effects can lead to over- orunderestimation of the layer/rim compositions of the concentricinclusions. Some inclusions contain tiny metal and sulfide grains.

Fe and Ni of these phases were analyzed as oxides which lead tosmall errors in the oxide concentrations. Other possible errors inthe determination of the bulk composition may result from theoccurrence of some CaCO3/CaSO4 within the pores of the CAIresulting from terrestrial alteration (e.g., 1476C/10, 1471/3L,1476B/12, 1476C/8L, and DfrB/2L). Natural and syntheticstandards of well-known compositions were used as standards.These are jadeite (Na), sanidine (K), diopside (Ca), apatite (P),V-metal (V), kyanite (Al), fayalite (Fe), chromite (Cr), fluorite (F),NiO (Ni), hypersthene (Si), forsterite (Mg), rhodonite (Mn), rutile(Ti), tugtupite (Cl), scapolite (S), and willemite (Zn). The matrixcorrections were made by the Fr(z) procedure of Armstrong(1991).

We tried to mass balance the bulk compositions usingthe compositions and the modal mineralogy of the observedphases within the inclusions. The modes calculated by massbalance are consistent with what is observed in the BSEimages, except for some inclusions. The causes can be (a) thedominant phase in the CAIs, spinel, is zoned. (b) The alterationphases are extremely inhomogeneous and also contain veryfine-grained unaltered phases (e.g. spinel, fassaite, ilmenite,etc). These alterations are highly porous and the pores andvoids are sometimes filled by terrestrial alteration products.(c) In some inclusions perovskite is rimmed by ilmenite.(d) Sometimes the whole CAI is very fine-grained and containsinhomogeneous mineral assemblages and significant porespaces. These constraints prohibit an exact estimationof the modal abundances of distinct components within theinclusion for final mass balancing of the bulk composition.Inclusions which could not be mass balanced are indicated inTable 2.

Classification of Al-rich objects in R chondrites

Rout and Bischoff (2008) studied the mineralogy and petrologyof 20 R chondrites and discovered 126 Al-rich objects (101 CAIs,19 Al-rich chondrules, and 6 Al-rich fragments) in 15 of them (noAl-rich objects were found in Hammadah al Hamra 119, Sahara99537, NWA 053, NWA 1477, and NWA 3364; Table 1). Theyfound that (a) most of the inclusions and fragments are verysmall, o50–150 mm, with the largest being 600�200 mm inapparent size; (b) they are relatively rare and intermediatein abundance between those in carbonaceous and ordinarychondrites: CC4RC4OC4EC; (c) on the basis of size, the CAIscompared to the various chondrite groups as: CV4CMECO4CR4RCZCH4OC4EC; (d) there is a marked difference inmineralogy between the CAIs in R3 chondrites (or brecciafragments of type 3) compared with those from types R4 to R6(or breccia fragments of types 4 to 6). The CAIs in themetamorphosed lithologies are heavily modified by thermalannealing, and most have oligoclase and spinel as the dominantminerals; (e) melilite, an abundant phase in CAIs of many otherchondrite groups (e.g., MacPherson et al., 1988; MacPherson, 2003;Brearley and Jones, 1998) and grossite (abundant in CR and CHchondrites; e.g., Bischoff et al., 1993a,b; Weber and Bischoff, 1994)were not found in refractory inclusions in R chondrites; (f) exceptfor a few objects, most are significantly altered and their pristinemineral assemblage is lost. On the basis of the alteration in CAIs inthe type 3 lithologies, portions of the original mineral assemblagescan be deduced, making the assumption that melilite was thephase which was modified to produce some of the Na,Al-richalteration; and (g) the mineralogy of the CAIs in R chondrites isquite unique, although there are some similarities with CAIs foundin CM, CO3, and ordinary chondrites.

S.S. Rout et al. / Chemie der Erde 70 (2010) 35–5336

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Based on the dominant mineral phases present and theirtextural characteristics, the Al-rich objects were divided by Routand Bischoff (2008) into six major groups: (1) Simple concentricspinel-rich CAIs; (2) Fassaite-rich spherules; (3) Complex spinel-

rich CAIs; (4) Complex diopside-rich inclusions; (5) Al-richchondrules; and (6) Al-rich fragments (Table 1). These groupswere further divided into various subgroups depending upon thesecond most abundant mineral present.

Fig. 1. BSE images of Ca,Al-rich inclusions in R chondrites. (a) Inclusion RA/911 is a round, simple concentric spinel-rich CAI, with abundant spinel and ilmenite and minor

hibonite. A thin rim of diopside surrounds the entire inclusion, and the interface between rim and spinel-rich core is filled with abundant Na,Al-rich alteration products.

(b) A simple concentric spinel- and hibonite-rich CAI (2446D/2L) with a hibonite core surrounded by abundant fine grained spinel. Numerous ilmenite grains are scattered

throughout and the entire inclusion is rimmed by diopside. (c) Simple concentric spinel- and fassaite-rich CAI, D013B/15. It has a core consisting of a mixture of spinel and

fassaite which is overlain by a thick diopside rim. Minor perovskite is also present. (d) Fassaite-rich spherule 753B/14 has a large spinel grain within a fassaite groundmass.

(e) A complex spinel- and fassaite-rich inclusion (753/131) with a sinuous rim of diopside overlying a core of a fine-grained mixture of spinel and fassaite. (f) Complex

spinel- and plagioclase-rich inclusion, 753B/6L, having abundant oligoclase and fine grained spinel. Sp=Spinel; Dp=Diopside; Fas=Fassaite; Hb=Hibonite; Olg=Oligoclase;

Alt=Na,Al-rich alteration; Ilm=Ilmenite; Prv=Perovskite; Olv=Olivine. BSE images.

S.S. Rout et al. / Chemie der Erde 70 (2010) 35–53 37

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Fig. 2. BSE images of Al-rich chondrules. (a) Al-rich chondrule, 2446D/71. It has porphyritic olivine grains within a matrix of elongated anorthite and interstitial diopside

and olivine. The olivine crystals show remarkable zoning. (b) DfrB/12 exhibits a thick forsteritic rim enclosing a core having barred olivine crystals within a mesostasis

consisting of fassaite and plagioclase. (c) Al-rich chondrule, 2446/71B has porphyritic olivine crystals which are zoned. The olivine crystals occur in a matrix of elongated

plagioclase laths and an interstitial material showing intergrowths of diopside and plagioclase. (d) Glass-rich chondrule, 2446C/51 with a thick rim of zoned olivine and a

core of Na,Al-rich glass embedding euhedral olivines. (e) Al-rich chondrule, 1476/74 is rich in olivine and has a thick rim of olivine. Numerous euhedral forsteritic olivine

crystals occur within a glassy mesostasis. Area marked by a square is shown in detail in f. (f) High magnification image of the glassy mesostasis within the Al-rich chondrule

1476/74. Two different types of glass are present within the matrix: Na-, K-, Si- and Al-rich glass and Ca-, Si- and Al-rich glass. Numerous crystallites are present within the

glass whose identity is difficult to decipher due to their small size. BSE images. Olv=Olivine, Dp=Diopside, An=Anorthite, Fas=Fassaite, Tr=Troilite.

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Bulk chemical composition of Ca,Al-rich objects

Simple concentric spinel-rich inclusions

Petrographically most of the inclusions are spinel-rich and,taking into account the other mineral phases present, they weredivided into four different subgroups. Due to the high spinelcontents, the Al2O3 and MgO values are high and, as the spinelshave high hercynitic content, the FeO value is also high. Except forthe inclusions containing fassaite, the low CaO and sometimes lowSiO2 values are consistent with near absence of any CaO-bearingmineral phases except for the rim diopside and minor fassaite.Some inclusions from all groups have high NiO contents (Table 2).This is mostly attributed to the presence of very fine-grained metalsand sulfides in many of the inclusions, which are difficult to beresolved, and from some NiO in spinel (Rout and Bischoff, 2008).

Simple concentric spinel-rich CAIs

All CAIs in this group have higher proportions of spinelcompared to the other inclusions (Fig. 1a). Al2O3 ranges from

�21 to 57 and MgO from �7 to 21 wt% (Table 2; all % in the textand tables are in wt.%). The lower Al2O3 in some inclusions is dueto the presence of thick diopside rims which is further expressedthrough the significant amounts of SiO2 (�9–29%). The rimdiopside is mostly high-Ca pyroxene and a corresponding increasein bulk CaO is therefore also observed in inclusions with thickrims. All the inclusions of this group fall along a linear mixingtrend between the spinel (�71% Al2O3) and diopside (�26% CaO)end members, although more skewed towards the spinel end inthe CaO vs. Al2O3 plot (Fig. 3a). One CAI (753/116B) has abundantFe-rich olivine, ilmenites, and some metals along with spinel andconsequently high FeO (36.2%) and NiO (4.1%) and lower Al2O3

(21.1%) content. Except for inclusions in the unequilibrated type 3R-chondrite lithologies, CAIs in the metamorphosed portions areheavily altered by metasomatism (Fe-alkali metasomatism).Consequently, FeO contents are sometimes extremely high(1.7–36%), along with variable ZnO (up to 2.2%). The high FeO isdue to the increase in the hercynitic component of the spinel withprogressive metasomatism. The bulk compositions plot wellbelow the Ca/Al cosmic line (Fig. 3a), due to the low bulk CaO

Table 1Characterization and listing of R chondrites and their Al-rich objects studied. Superscripts in column 2 indicate the references listed in the footnote.

Meteorite Class Concentric spinel-

rich CAIs

Fassaite-

rich

spherules

Complex spinel-rich CAIs Complex

diopside-

rich CAIs

Al-rich

chondrules

Al-rich

fragments

Rumuruti R3-51,2 RA/43A, RA/43B,

RA/911

RA/21, RA/53M RB/41M

Sahara 99531 R3-54 ShrB/41M – – – – –

Acfer 217 R3-55 Afr/4LM Afr/61M, Afr/111M

Dar al Gani 013 R3.5-66,7 D013/23, D013/44,

D013B/15,

D013B/35M,

D013B/118

– D013/24, D013B/65M,

D013B/119M

– D013B/71M,

D013B/144M,

D013B/183M

–

Dar al Gani 417 R3-48 – – D417/43M – D417/61M –

Hughes 030 R3-69 H030/LM H030/22M H030/2LM

Dhofar1223 R310 DfrB/2L Dfr/23 Dfr/53, Dfr/75 DfrB/12,

DfrB/32M

NWA 753n R3.911 753/73, 753/102,

753/104A, 753/104B,

753/111, 753/116A,

753/116B, 753/143M,

753/154M, 753B/13,

753B/34, 753B/62,

753D/64, 753D/74,

753_124/23M,

753_124/12LM

753B/14M 753/1LM, 753/24M,

753/31AM, 753/22M,

753/31BM, 753/35M,

753/37M, 753/42M,

753/44, 753/46, 753/4LM,

753/52, 753/6L,

753/93, 753/95,

753/116C, 753/11L,

753/12LA,753/131,

753B/33, 753B/6LM,

753C/31, 753C/51M,

753D/54, 753_124/21M

753C/21 753/12LB,

753B/23,

753_124/33M

NWA 755 R3.711 – – 755/31M – 755/13BM,

755/33M

755/13M

NWA 1471 R3/412 – – 1471/23M, 1471/3LM – – –

NWA 1472 R3/412 1472/12M, 1472/56M – 1472/15M, 1472/117M,

1472/119M,

1472/175M

– – –

NWA 1476n R312 1476/83, 1476C/62A,

1476C/8L

1476/124 1476B/12, 1476C/54,

1476C/62B,

1476C/101, 1476C/102

– 1476/22,

1476/74,

–

NWA 1478 R312 1478/12M – 1478/35M – – –

NWA 1566 R3.812 1566/32M

NWA 2446n R310 2446/23, 2446/33,

2446/84, 2446/112,

2446/L, 2446B/8L,

2446D/2L

– 2446/12, 2446/31B,

2446/71A, 2446/122B,

2446B/1L, 2446B/54,

2446D/33A, 2446D/33B,

2446D/41

2446/31A,

2446/63,

2446/122A

2446/71B,

2446/85M,

2446B/9L,

2446C/51,

2446D/71

2446B/5L

M=inclusions from metamorphosed lithologies. Since many meteorite samples are breccias we found CAIs within metamorphosed and unmetamorphosed lithologies

within the same thin section. Inclusions from metamorphosed lithologies are mostly characterized by the presence of oligoclase and absence of Na,Al-rich alteration

products.

(1)Schulze et al. 1994; (2)Berlin 2003; (3)Weber et al. 1997; (4)Grossman 2000; (5)Bischoff et al. 1994; (6)Jackel et al. 1996; (7)Grossman 1996; (8)Grossman 1999;

(9)Grossman 1998; (10)Russell and Zolensky, 2005; (11)Grossman and Zipfel 2001; (12)Russell et al. 2003.

n NWA 753, 2446, 1476, and 1477 are breccias.

S.S. Rout et al. / Chemie der Erde 70 (2010) 35–53 39

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41

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10

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80

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98

.29

S.S. Rout et al. / Chemie der Erde 70 (2010) 35–5340

Author's personal copyARTICLE IN PRESS

Co

mp

lex

spin

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an

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24

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S.S. Rout et al. / Chemie der Erde 70 (2010) 35–53 41

Author's personal copyARTICLE IN PRESS

values and high spinel contents. In the Na2O+K2O+Cl vs. FeO plot(Fig. 3b), most inclusions plot at the high FeO-end. The generalabsence of Na,K-rich phases leads to low Na2O and K2O values(Table 2; Fig. 3b, c). Two inclusions (1566/23 and RA/911; Fig. 1dof Rout and Bischoff, 2008 and Fig. 1a, respectively) have higherNa2O contents, compared to other simple concentric spinel-richinclusions, and plot within the field of simple concentric spinel-and Na,Al-alteration product-rich CAIs field (Fig. 3c). But weclassified them as simple concentric spinel-rich CAIs due to theirsignificantly higher contents of spinel. On the basis of the bulkcomposition, these inclusions are very similar to some of thespinel-pyroxene inclusions in the CM2 chondrite Mighei(MacPherson and Davis, 1994) and to some spinel–pyroxeneinclusions in the ungrouped C3 meteorite Ninquiang (Lin andKimura, 2003). The Mighei spinel–pyroxene inclusions haveaverage �45% Al2O3, �10.2% CaO, �18.5% MgO and �9.4% FeO.

Simple concentric spinel- and hibonite-rich CAIs

These inclusions are very rare (e.g., Rout and Bischoff, 2008),and two of the three studied (Fig. 1b) are affected by severeterrestrial alteration and have high S as a consequence. Al2O3

ranges from �37–72%, and the low value is probably due to thepresence of abundant alteration products, and the high value isprobably an overestimation as the inclusion (H030/L) has largevoids and, thus, the analysis may be biased towards the hibonites.All three inclusions are secondarily modified either due toterrestrial processes or by preterrestrial Mg/Fe-exchange andalkali metasomatism, which produced the FeO-rich spinels andNa-,Al-rich alteration products; bulk FeO ranges from �5.5–23%(Table 2; Fig. 3b). Recent isotopic analysis (Rout et al., 2009) hasshown that H030/L is a HAL-type inclusion (Lee et al., 1979; Daviset al., 1982; Hinton and Bischoff, 1984; Ireland and Compston,1987; Ireland et al., 1992; Ushikubo et al., 2007b).

Simple concentric spinel- and fassaite-rich CAIs

These inclusions are very similar to the simple concentricspinel-rich CAIs except for the presence of fassaite (Fig. 1c; we areusing the word ‘‘fassaite’’ to denote the Al–Ti-diopside orsubsilicic titanoan aluminian pyroxene). Consequently, Al2O3 ishigh (�23–52%), along with MgO (�7–20%) and CaO (�2.5–17%).When Al2O3 is relatively low, the fassaite content seems to behigh, and a corresponding increase in SiO2 and CaO is seen. Mostinclusions are devoid of Na-, K-, and Cl-rich volatile alterationsand have low Na2O and K2O, and some are among the chemicallymost unaltered (primitive) CAIs in R-chondrites (Fig. 3b).However, FeOn can be high (�2–22%), due to alteration of spinel(Mg/Fe-exchange). These inclusions plot closer to the cosmicCa/Al-line (Fig. 3a) compared with the simple concentric spinel-rich CAIs, but are still far away from the solar ratio. This is due tothe inherently high abundance of spinel and relatively lowamounts of fassaite in some inclusions. Only one inclusion2446/23 (Table 2) seems to plot close to the cosmic line. Similarto the simple concentric spinel-rich CAIs, this group of CAIs alsoplots along a general linear trend between the spinel and thepyroxene end-members in the CaO vs. Al2O3 plot (Fig. 3a). Thesimple concentric spinel- and fassaite-rich CAIs are more wide-spread between the spinel and diopside end members ascompared to the simple concentric spinel-rich CAIs, mostly dueto their higher pyroxene content. If we consider these inclusionsas binary mixtures of spinel and pyroxene (diopside), a roughestimation shows that only a ratio of spinel: pyroxene of �32:68results in an approximately cosmic CaO/Al2O3 ratio of 0.8 (CaO:�17.8% and Al2O3: �22.5%). Except one (2446/33) all theinclusions have an overabundance of spinel as compared to theabove cosmic ratio.T

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S.S. Rout et al. / Chemie der Erde 70 (2010) 35–5342

Author's personal copyARTICLE IN PRESS

These inclusions are also similar in composition to the averagecompositions of the spinel-pyroxene inclusions in Mighei (MacPher-son and Davis, 1994). Furthermore, some inclusions from theungrouped Ninquiang C3 meteorite also have similar bulk composi-tions (Lin and Kimura, 2003). Fine-grained spinel-rich inclusions fromthe reduced CV chondrites Leoville and Efremovka have higher SiO2

(22.8–40.5% vs. 11.2–23.0%) and CaO (15.9–24.7% vs. 2.5–17.2%),similar/lower Al2O3 (23.6–43.6% vs. 27.4–52.1%) and lower MgO(10.7–16.8% vs. 8.2–19.7%) than the simple concentric spinel- andfassaite-rich CAIs (Krot et al., 2004b). However, when comparingthese inclusions with the type B2 inclusions in CV3 chondrites (e.g.,Wark and Lovering, 1982; Grossman et al., 2000, 2008; Simon andGrossman, 2004), those in R chondrites have significantly lower CaO(maximum of 16.7 vs. 22–30% in CV3s). Further, they have similarMgO (�7–20 vs. 10–16%), significantly higher Al2O3 (23–52 vs. 25–28%), and lower SiO2. For comparison, Type A inclusions from CV3chondrites have much lower MgO (�5–12%) and higher CaO (�28–37%), but similar Al2O3 (33–42%) and SiO2 (18–26%) (e.g., Grossman,1975; Grossman et al., 2000, 2008; Simon and Grossman, 2004).

Simple concentric spinel- and Na,Al-alteration product-rich CAIs

Most of these inclusions have high amounts of alterationproducts, along with the usually dominating spinel. Consequently,Na2O can be as high as 12.5% (Table 2; Fig. 4 of Rout and Bischoff,2008), although it is significantly lower in most of the otherinclusions (ShrB/41; Na2O=1.2%; Fig. 4d of Rout and Bischoff,2008). Al2O3 is usually high due to the high spinel content and theremarkably high SiO2 contents are due to the presence ofNa,Al-rich alteration products such as nepheline and/or sodalite.All of these objects plot well below the cosmic line as do thesimple concentric spinel-rich and the simple concentric spinel-and fassaite-rich CAIs (Fig. 3a). However, they are clearlyresolvable in Fig. 3b and are the most heavily altered inclusions,as indicated by high alkali and Fe contents (alkali- and Fe-metasomatism). In Fig. 3c these inclusions show a positivecorrelation between the Na2O and SiO2 contents, which indicatesa progressive increase in both the components with increase inalteration most probably due to the formation of nepheline/sodalite and of oligoclase within the CAIs from metamorphosed

Fig. 3. Binary plots for different refractory inclusions within the R chondrites. (a) CaO vs. Al2O3 for Al-rich objects in R chondrites. The cosmic Ca/Al line (Lodders, 2003) is

also shown. Points marked by a, b, c, d, and e are related to the inclusions 1476C/10, 1471/3L, 1476B/12, 1476C/8L, and DfrB/2L. They contain CaCO3 as a terrestrial

alteration phase and, consequently, have high CaO concentrations. (b) Na2O+K2O+Cl vs. FeO for all inclusions studied in R chondrites. A break in the FeO axis from 25% to

32% has been added to better illustrate the high FeO content in one inclusion. Same labels as in (a). (c) Na2O vs. SiO2 for the Al-rich objects in R chondrites. The complex

spinel- and plagioclase-rich CAIs (grey squares) with Na2O above about 1 wt% are oligoclase-rich and from metamorphosed lithologies. Symbols are as in (a). Con

Sp=Simple concentric spinel-rich CAIs; Con Sp-Ne/So=Simple concentric spinel- and Na,Al-alteration product-rich CAIs; Con Sp-Fas=Simple concentric spinel- and

fassaite-rich CAIs; Con Sp-Hb=Simple concentric spinel- and hibonite-rich CAIs; Com Sp-Plg=Complex spinel- and plagioclase-rich CAIs; Com Sp-Fas=Complex spinel- and

fassaite-rich CAIs; Com Sp-Ne/So=Complex spinel and Na,Al-alteration product-rich CAIs; Com Sp-Hb=Complex spinel- and hibonite-rich CAIs; Fas Sphr=Fassaite-rich

spherules; Com Dp=Complex diopside-rich CAIs; Al-rich Chond=Al-rich chondrules.

S.S. Rout et al. / Chemie der Erde 70 (2010) 35–53 43

Author's personal copyARTICLE IN PRESS

lithologies. They are similar in bulk composition to the irregularlyshaped inclusions in enstatite chondrites (Bischoff et al., 1985),although the FeO contents of the irregularly shaped inclusions arelower and the MgO contents are higher. This can be explained bythe low FeO in the enstatite chondrite CAIs. Some of the refractoryirregularly-shaped inclusions in ordinary chondrites (Bischoff andKeil, 1983a) have similar bulk compositions. The Allende fine-grained inclusions (Grossman and Ganapathy, 1975) are alsohighly altered, but in comparison to the simple concentric spinel-and Na,Al-alteration product-rich CAIs in R-chondrites havehigher CaO (�11% vs. 0.81–15%), slightly lower Na2O (1.3–4%vs. 1.22–12.5%), and higher MgO (�12–15% vs. 3.2–16.5%). Fine-grained inclusions from Leoville and Efremovka are least alteredand have low Na2O (o0.2%) and higher CaO (15.9–24.7% vs. 0.81–15%), similar/higher SiO2 (22.8–40.5% vs. 4.6–37.4%) and similarAl2O3 (23.6–43.6% vs. 20.7–54.3%) contents as compared to thesimple concentric spinel- and Na,Al-alteration product-rich CAIsin R chondrites.

Fassaite-rich spherules

The three spherules analyzed have higher CaO and SiO2,compared to above described concentric inclusions (Table 2),although significant differences exist between the individualspherules. These differences are mostly the result of differencesin their mineralogy, as one contains hibonite, the other spinel(Fig. 1d), and the third has spinel and olivine (Rout and Bischoff,2008). Fassaite is the carrier of high CaO, MgO, and SiO2, and theFeO in Dfr/23 seems to be inherent to it and not a result of postaccretionary metamorphism, as it contains two different varietiesof olivine and elemental mapping did not show any zoning in FeO(Rout and Bischoff, 2008). However, in 753B/14, the high bulkFeO is attributed to the high hercynitic component in its spinel(Fig. 1d). 1476/124 contains hibonite laths within a fassaitegroundmass, and similar hibonite-pyroxene spherules have alsobeen reported from other chondrites (e.g., Kurat, 1975; Grossmanet al., 1988; MacPherson et al., 1989; Ireland et al., 1991; Tomeokaet al., 1992; Russell et al., 1998; Simon et al., 1998). It has a bulkcomposition similar to the hibonite–pyroxene and hibonite–glassspherules in the ALH 85085 CH chondrite (e.g., Grossman et al.,1988; MacPherson et al., 1989), Lance CO3 chondrite (e.g., Kurat,1975; Ireland et al., 1991), Murchison CM2 chondrite (Irelandet al., 1991), Murray CM2 chondrite and Yamato 791717 CO3chondrite (e.g., Simon et al., 1998; Tomeoka et al., 1992), and theColony and ALH82101 CO3 chondrites (Russell et al., 1998)(Table 3). The hibonite bearing fassaite-rich spherule 1476/124

plots relatively closely to the cosmic Ca/Al line (Fig. 3a) and hasthe lowest FeO (i.e., is the least altered) among all the CAIs(Fig. 3b), whereas Dfr/23 plots above and 753B/14 below thecosmic Ca/Al line. Fig. 4 shows that the spinel bearing spheruleshave a cosmic TiO2/Al2O3 value, but spherule 1476/124 plots in thegroup of other hibonite–pyroxene and hibonite–glass spherules.

Complex spinel-rich CAIs

The complex spinel-rich CAIs are subdivided into differentgroups based on their mineralogy (Rout and Bischoff, 2008). Incontrast to the simple concentric spinel-rich CAIs, the complexspinel-rich CAIs have slightly lower spinel contents, and this isevidenced by their lower bulk Al2O3 in many inclusions. Againmany inclusions have high NiO contents due to the presence offine-grained metals that are difficult to be resolved except in fewof the inclusions.

Complex spinel- and hibonite-rich CAIs

These inclusions are similar to the simple concentric spineland hibonite rich CAIs, are very rare in our suite of samples (onlytwo were found; Fig. 6 of Rout and Bischoff, 2008), and their Al2O3

is high (�35 and 55%). Due the presence of abundant alterationproducts, their SiO2 and Na2O contents are also high (Table 2).

Table 3Comparison of the bulk composition of the hibonite-bearing fassaite-rich spherule 1476/124 in the R chondrite NWA 1476 with hibonite–pyroxene and hibonite–glass

spherules from different chondrites.

CAI L3413/31a M7-228b M7-753b MYSM3c Y17-6c SP1d SP15d 1476/124

MgO 6.3 7.2 5.3 6.1 5.1 5.4 5.1 5.9

Al2O3 35.1 28.9 47 37.4 39.3 44.9 44.0 33.9

Cr2O3 n.a. n.a. n.a. n.a. n.a. n.a. n.a. 0.05

SiO2 33.1 39.4 27.3 31.3 29.3 26.7 27.2 32.8

CaO 23.8 22.6 17.9 23.5 23.1 20.1 21.3 23.3

FeO n.a. n.a. n.a. n.a. n.a. 0.43 0.38 0.42

TiO2 1.7 1.8 2.6 1.67 3.22 2.16 3.26 2.62

ZnO n.a. n.a. n.a. n.a. n.a. n.a. n.a. o0.01

Total 100 99.9 100.1 99.97 100.02 99.69 101.24 98.99

Superscript numbers indicate the references. n.a.=not analyzed, n.d.=not detected.

a Kurat (1975), Ireland et al. (1991).b Ireland et al. (1991).c Simon et al. (1998).d Russell et al. (1998).

Fig. 4. TiO2 vs. Al2O3 for the R chondrite fassaite-rich spherules along with those

from other chondrite groups. Also plotted is the cosmic Ti/Al ratio line (Lodders,

2003). Numbers in parentheses next to the inclusions are the references:

1=Russell et al., 1998; 2=Ireland et al., 1991; 3=Simon et al., 1998.

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Complex spinel- and fassaite-rich CAIs

Most of these inclusions consist of a complex fine- to coarse-grained mixture of spinel and fassaite (Fig. 1e) with, occasionally,abundant alteration products that are responsible for the highbulk Na2O (Table 2). Other inclusions have only minor alterationconstituents, and some are totally free of alteration products andare among the most primitive inclusions in R chondrites whichaccounts for their low FeO, Na2O, and K2O (Fig. 3b). The inclusionswith abundant alteration show a linear increase in their Na2O andSiO2 contents with progressive increase in alteration (Fig. 3c).Bulk Al2O3 is relatively low (�16–58%), and high bulk SiO2 andCaO and a corresponding increase in TiO2 were found in some,due to abundant fassaite. Some inclusions plot on or above thecosmic Ca/Al line (Fig. 3a), whereas others with high contentsof alteration products plot below the line. Similar to the simpleconcentric spinel- and fassaite-rich inclusions (see above) onlyone of the inclusions (D013/24) has the modal spineland pyroxene abundance to approximately equal the cosmicCaO/Al2O3 ratio of 0.8.

Some similarities in composition are noted with previouslydescribed objects in other meteorite types. For example, some ofthe irregularly shaped inclusions in ordinary chondrites (Bischoff andKeil, 1983a, b, 1984) have similar bulk compositions, and so do thespinel-pyroxene inclusions in the Mighei CM2 chondrite (MacPhersonand Davis, 1994). Also, most of the spinel-pyroxene inclusions in the

ungrouped Ninquiang C3 meteorite have similar bulk compositions.There are also similarities in bulk composition to the fine-grainedinclusions in the Efremovka and Leoville (Krot et al., 2004b) andAllende CV3 meteorites (Grossman and Ganapathy, 1975) (Fig. 5).

Complex spinel- and plagioclase-rich CAIs

These inclusions contain either oligoclase (Fig. 1f) or An-richplagioclase. Those with An-rich plagioclase occur in unequili-brated type 3 lithologies, and anorthite is certainly a primaryphase. On the other hand, oligoclase appears to be the mainNa-bearing phase formed during metamorphism. These inclusionsare the most abundant type of Al-rich objects in the metamor-phosed R chondrite lithologies, with relatively high bulk Na2O andSiO2 (Table 2; Fig. 3c), and the lower Al2O3 in some results fromtheir lower contents of spinel and the lower Al2O3 in oligoclase.These inclusions, with abundant oligoclase, clearly plot along apositive linear trend in a Na2O vs. SiO2 plot (Fig. 3c). Thiscorrelation reflects the increase in Na2O and SiO2 contents ofthese CAIs during metamorphism due to the formationof oligoclase. These CAIs plot well below the Ca/Al cosmic line(Fig. 3a) and at high Na2O+K2O+Cl and FeO ends (Fig. 3b).The anorthite-bearing inclusions (753/6L, 753C/51, 1472/175,753/12LA, 1471/3L; Table 2) are the most primitive and leastaltered in this group, although they are also affected by somemetamorphic effects. The fine grained inclusions, specially the

Fig. 5. Variations in bulk compositions of (a) Al2O3 vs. TiO2, (b) FeO vs. MgO, and (c) Al2O3 vs. MgO for Al-rich chondrules from Rumuruti chondrites. Also shown are Al-rich

chondrules from ordinary chondrites (Bischoff and Keil, 1983c). Cosmic proportions of the oxides (Lodders, 2003) are shown in (a) and (b).

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high-Rb aggregates in the Allende CV3 meteorite (Grossman andGanapathy, 1975), are similar in composition to the anorthite-bearing inclusions, and these are also similar to the Type Cinclusions (Wark, 1987), which have CaO, MgO, and Al2O3

contents of �13–26, 4–14, and 13–46%, respectively.

Complex spinel- and Na,Al-alteration product-rich CAIs

These inclusions are heavily altered, have high volatilecontents such as Na2O, K2O, Cl, and FeO (Table 2; Figs. 4, and 9of Rout and Bischoff, 2008), are similar in bulk composition tothe simple concentric spinel- and Na,Al-alteration product-richCAIs (Fig. 3a, b), and the alteration phases are mostly nephelineand sodalite. The low Na2O of inclusion 2446B/54 (Table 2), whichhas high apparent porosity, is probably an artifact and dueto removal of the alteration products during thin sectionpreparation. Some of the inclusions contain highly porousfine-grained aggregates that are rich in Na and K. Due to theirinherent high porosity lower oxide totals were obtained duringthe microprobe analysis.

Complex diopside-rich CAIs

These unique inclusions have a highly convoluted texture andare rich in diopside (Fig. 10 of Rout and Bischoff, 2008). They donot contain abundant spinel and are very porous and heavilyaltered. Consequently, Al2O3 (�11–22%) is low and SiO2 (42–44%)and CaO (14–20%) are higher than in the spinel-rich CAIs(Table 2). Two of the inclusions plot very close to the cosmicCa/Al line (Fig. 3a).

Al-rich chondrules

Al-rich chondrules have previously been described fromordinary (e.g., Bischoff and Keil, 1983a, b, 1984; Bischoff et al.,1989), and enstatite and carbonaceous chondrites (e.g., Bischoffet al., 1984; Sheng et al., 1991; Krot et al., 2002, 2004a;MacPherson and Huss, 2005; Huss et al., 1997, 2001; Guanet al., 2002; Russell et al., 1996, 2000; Srinivasan et al., 2000;Tronche et al., 2007). Following the earlier work of Bischoff andKeil (1983a, b, 1984) all chondrules with Al2O3 Z10% are referredhere as Al-rich chondrules. Most have significant Na2O and FeO(Table 2), although Al-rich chondrules with minor Na and/or Fewere also analyzed. Most of the bulk FeO results from the highfayalite content of olivine, whereas major Na2O is due to therelatively high amounts of Na-rich plagioclase. However, inchondrules 2446C/51, 1476/74, and 753C/21 (Fig. 2d–f), the highbulk Na2O is attributed to the presence of Na,Al-rich glass. Most ofthese chondrules plot below but near the cosmic Ca/Al line(Fig. 3a). The high volatile element abundances of the chondrulesare further exhibited in the FeO vs. Na2O+K2O+Cl plot (Fig. 3b). Ina TiO2 vs. Al2O3 plot, most Al-rich chondrules in R chondrites donot plot along the cosmic line, whereas those of ordinarychondrites do. Some are similar in bulk composition to thosefound in the enstatite chondrites (Bischoff et al., 1985), althoughmost of the enstatite chondrite Al-rich chondrules have lower FeOand higher SiO2 and MgO.

Discussion

Origin of CAIs from R chondrites

Most of the CAIs in R chondrites are similar to the spinel–pyroxene and fine-grained inclusions found in other chondrites.Recent oxygen isotopic analyses of some R chondrite CAIs also

suggest that, except for a few significant differences, they are ingeneral similar to the CAIs found in other chondritic groups (Routet al., 2009). Different hypotheses have been proposed for theorigin of the spinel–pyroxene CAIs. Cohen et al. (1983) andKornacki and Fegley (1984) suggested that spinel-rich inclusionsare distillation residues of small primitive dust aggregates. Basedon the presence of fractionated Group II REE patterns and absenceof any enrichment of heavy Mg isotopes in the spinel–pyroxeneinclusions in the CM chondrite Mighei, MacPherson and Davis(1994) proposed that the recrystallized spinel-rich objects formedby the melting of the fine-grained, porous spinel–pyroxene-richaggregates and the porous aggregates formed by disequilibriumcondensation of a gas already depleted in refractory REE. Similargroup II REE pattern and presence of light Mg isotopes has alsobeen observed in many fine-grained spinel rich inclusion and,therefore, a gas-solid condensation origin has been proposed (e.g.,Boynton, 1975; Brigham et al., 1985, 1986; Lin and Kimura, 2003).Grossman and Ganapathy (1975) and Grossman (1975) foundfine-grained spinel-rich inclusions in carbonaceous chondrites,similar to some of the CAIs in R chondrites that are enriched inrefractory Ca, Sc, Ta, and REE as well as in volatile elements. Theysuggested that these fine-grained spinel-rich inclusions formed bysimultaneous condensation of refractory and volatile lithophileelements that failed to condense into coarse-grained inclusions.

Texturally some of the inclusions studied here clearly showthat they have crystallized from a melt, whereas others are porousaggregates of minerals which have not experienced melting (Routand Bischoff, 2008). The crystalline inclusions may be distillationresidues (Cohen et al., 1983; Kornacki and Fegley, 1984). Thesimple concentric spinel-rich inclusions, which have only spinelwith a pyroxene rim, have high Al2O3 and their origin cannot beexplained by an equilibrium condensation process. They plotmuch below the cosmic Ca/Al line (Fig. 3a), suggesting that therehas been some fractionation event which increased Al2O3 relativeto CaO as well as the spinel content. These inclusions also have acosmic Si/Mg ratio, indicating that CaO is highly depleted in them.Partial melting can lead to the formation of CaO–MgO–Al2O3–SiO2

liquids, richer in CaO and SiO2, and a spinel-rich residue.Separation of this liquid by evaporation in a hydrogen-rich gas(Richter et al. 2002, 2007) already depleted in the constituentphases and splashing of the liquid could produce inclusionssimilar to the concentric spinel-rich CAIs. Further condensationshould lead to the formation of the diopsidic rim which increasedits SiO2 content to near cosmic values. Based on the texture, one ofthe simple concentric spinel-rich CAI (Fig. 1d in Rout and Bischoff,2008) is an excellent example of an inclusion formed by crystal-lization from a melt.

However, some concentric spinel-rich inclusions may haveformed by disequilibrium condensation on a pre-existing spinelgrain (MacPherson and Davis, 1994). Petaev et al. (2005) showedthat spinel can condense from the gas before melilite because ofincomplete condensation of all minerals condensing before spineldue to faster cooling rates (at pressures lower than 2.5�10�4

bar). Such a reaction can produce a spinel core with layers ofdiopside, which formed later by a reaction of melilite with the gas.Beckett and Grossman (1988) and Beckett and Stolper (1994)proposed that condensation of spinel can occur prior to meliliteformation due to kinetic effects or by extreme Ca/Al fractionation.The kinetic effect results from hibonite and spinel having similarcrystal structures, and this will allow spinel condensation onhibonite crystals prior to melilite condensation. However, nohibonite was found in any of the spinel cores except in theinclusion 2446B/8L (Fig. 2b of Rout and Bischoff, 2008).

The low FeO-bearing concentric inclusions have a mineralassemblage different from that predicted by a CMAS phasediagram (e.g., MacPherson and Huss, 2005; Beckett et al., 2006).

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Thus, crystallization from a melt cannot have produced theseinclusions. Simple concentric spinel- and fassaite-rich and simpleconcentric spinel- and Na,Al-alteration product-rich CAIs plotbelow the cosmic Ca/Al line (Fig. 3a) which can be attributed totheir higher contents of spinel and to severe secondary alterationwhich has changed the original Ca/Al ratio. The simple concentricspinel- and Na,Al-alteration product-rich CAIs have been alteredby incorporation of volatiles and formation of abundant nephelineand/or sodalite. Considering the alteration of earlier presentmelilite, significant amounts of the original Ca content of theinclusion have been lost. Also, the high modal spinel content inthe inclusions has further increased their Al content. To get acosmic CaO/Al2O3 ratio of 0.8 the modal spinel: pyroxene ratioshould be �32:68 (see above). All but one of the concentricspinel- and fassaite-rich CAIs have an overabundance of spinelcompared to this ratio. Thus, a mechanism, which significantlyincreased the spinel abundance relative to pyroxene, has to besuggested to explain the origin of these inclusions.

According to equilibrium condensation in a cooling gas of solarcomposition, hibonite reacts with gas to form gehlenitic meliliteat 1628 K and lower and later spinel at 1500 K. Gehlenitic melilitefurther reacts with gaseous Mg to form akermanitic melilite andspinel below 1500 K (e.g., Yoneda and Grossman, 1995; Gross-man, 1972). Most of the simple concentric spinel- and Na,Al-alteration product-rich CAI inclusions plot much below the Ca/Alcosmic ratio line, indicating that there has been some fractiona-tion of Al with respect to Ca at an initial stage for many inclusions.Disequilibrium condensation of spinel before melilite as statedabove is a possibility (e.g., Petaev et al., 2005; Petaev and Wood,2005). Thus, spinel preferentially condenses before melilite,followed by minor melilite. The mineral assemblage at this pointhas high abundances of spinel and melilite. At this stage, theinclusions did not further react with the gas and must have beenremoved from the nebular environment. Recent magnesiumisotopic analyses of hibonite in a simple concentric spinel- andhibonite-rich CAI (2446D/2L) show that they are rich in the lightMg isotope (Rout et al., 2009). This is a further indication that theinclusion formed by condensation from a gas that had alreadybeen depleted in refractory magnesium isotopes or most probablyby a disequilibrium condensation process, as stated above. All theabove explanation is based on the assumption that condensationtakes place from a gas of solar composition, which may not bealways true especially in a complicated and dynamic nebularenvironment. The light Mg-isotope enrichment of the abovementioned CAI (2446D/2L) is proof that it may have condensedfrom a gas that is non-solar in composition. Equilibriumcondensation from a gas of non-solar composition can producethe enrichments of a particular oxide, and consequently a mineral(e.g., spinel). The abundances of spinel in most of the inclusionscan also be explained by their condensation from a non-solarcomposition gas.

After melilite and spinel have condensed below 1500 K, eitherby equilibrium or disequilibrium processes from a solar composi-tion gas, the former reacts with perovskite and minor spinel at1449 K to form fassaite (e.g., Yoneda and Grossman, 1995;Grossman, 1972; Petaev et al., 2005). The simple concentricspinel- and fassaite-rich inclusions (Fig. 1c; Fig. 3 of Rout andBischoff, 2008) appear to be the next product of the reaction of themelilite- and spinel-rich inclusions with the nebular gas. Thisreaction must have increased the SiO2 content within the fassaite-rich inclusions and we also see higher SiO2 in them as comparedto the Na,Al-alteration product-bearing CAIs (Table 2). Here, weassume that the earlier present melilite has been altered to Na,Al-rich alteration products. Alterations of melilite and spinel havesignificantly modified the primordial composition of the inclu-sions, which makes a direct comparison between the two

inclusion groups difficult. In the above mentioned reaction ofmelilite with perovskite and spinel to form fassaite, a smallamount of spinel takes part in the reaction and this increases thespinel content of the inclusion after all the melilite is used upduring the reaction. For the concentric spinel- and fassaite-richinclusions, disequilibrium condensation of spinel prior to con-densation of melilite has to be proposed to account for the highbulk Al content of the inclusions. Again the presence of highercontents of Al2O3, and consequently spinel, in most of theseinclusions can be explained by their condensation from a gas ofnon-solar composition.

Some of the complex spinel-rich inclusions, which have fluffyand irregularly shaped textures, have mineral parageneses aspredicted by equilibrium condensation from a solar compositiongas (Yoneda and Grossman, 1995). Few inclusions of this groupplot close to the cosmic Ca/Al line (Fig. 3a). Almost all the complexspinel- and plagioclase-rich CAIs are too heavily altered todecipher their pristine mineralogy and origin (Fig. 1f). As statedbefore the oligoclase-bearing CAIs are from metamorphosed Rchondrite lithologies and Na-rich feldspar is a metamorphicproduct. Only a few of the complex spinel- and plagioclase-richinclusions are less altered, have primary anorthite and havetextures that indicate crystallization from a melt (Fig. 7 in Routand Bischoff, 2008. Oligoclase clearly seems to be the post-metamorphic product of Na,Al-rich alteration phases.

Some of the complex spinel- and fassaite-rich inclusionsformed by similar processes as the concentric spinel- andfassaite-rich CAIs, i.e., after reaction of the gas with a spinel–melilite–perovskite assemblage under equilibrium conditions orby disequilibrium condensation of spinel (Yoneda and Grossman,1995; Petaev et al., 2005). Some of the complex spinel- andfassaite-rich CAIs have a modal abundance of spinel and pyroxene(ratio: �32:68) that closely relates to the cosmic CaO/Al2O3-ratio(see above). Many others do not have this ratio, mostly becausethey are highly altered and do certainly not represent a primordialbinary mixture of spinel and pyroxene alone. However, for thoseinclusions, which are devoid of alteration, a cosmic mineralproportion may be a further proof to their condensation originfrom a solar composition gas. Again a condensation origin from anon-solar composition gas for many inclusions cannot be ruledout.

Further, some complex spinel- and fassaite-rich inclusionswith fluffy and porous textures (Fig. 8c, d of Rout and Bischoff,2008) may have formed by agglomeration of refractory dusts richin spinel and fassaite, similar to what has been suggested for theformation of the irregularly shaped inclusions in ordinarychondrites (Bischoff and Keil, 1983a, 1984). These refractorydusts may have been produced by non-equilibrium condensationof a solar gas or by condensation from a non-solar compositiongas and these phases later agglomerated along with some volatilephases.

As stated above, the concentric spinel- and hibonite-rich CAIH030/L is a HAL-type inclusion (Rout et al., 2009). Most of theHAL-type inclusions formed by extensive distillation of theirprecursor phases (Hinton and Bischoff, 1984; Ireland andCompston, 1987; Ireland et al., 1992), which has also beensubstantiated by laboratory experiments (e.g., Floss et al., 1996;Wang et al., 2001). The H030/L hibonites have a compositionsimilar to the average composition of hibonite 7-971,located in mineral separates from the Murchison carbonaceouschondrite (Ireland, 1988). The hibonite in residues of precursorsused in laboratory evaporation experiments that were subjectedto more than �97% mass loss and peak temperatures above2000 1C have a similar Al2O3 content as that of H030/L hibonite(e.g., Floss et al., 1996; Wang et al., 2001; Rout and Bischoff,2008). Thus, we conclude that inclusion H030/L formed by

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distillation during which it was heated above �2000 1C andsuffered high mass loss (�97–98%). The fine-grained rim waslater deposited after the heating episode by reaction with thenebular gas.

Finally, the overwhelming majority of inclusions do not havecosmic Ca/Al ratios. They have a mineral assemblage whichprobably formed after most of the Ca and Al had alreadycondensed. Such a scenario was also discussed for the origin ofthe Type A and Type B CAIs (e.g., Grossman et al., 2000, 2002,2008; Simon and Grossman, 2004). Most of the complex spinel-and fassaite-rich inclusions and only some complex spinel- andplagioclase-rich CAIs plot within the field of type A and B CAIs(e.g., Grossman et al., 2002; Simon and Grossman, 2004).Similar to the type A and B CAIs, some of these inclusions haveigneous textures and also suffered evaporation under a finitehydrogen pressure during which Mg and Si were vaporized, andthis can lead to the deviation of the composition from the cosmicvalue.

Origin of the fassaite-rich spherules

Bulk and isotopic compositions of hibonite–pyroxene (i.e.,hibonite–fassaite) spherules from various types of carbonaceouschondrites have previously been determined to infer theircrystallization histories. For example, Ireland et al. (1991) foundthat inclusion MUR7-228 lacks trace element equilibrium be-tween the glass and hibonites and concluded that the hibonitesare relict phases. However, the hibonite/glass partition coeffi-cients of Ti and the trace elements for MUR7-228 agree well withthe experimentally determined values, and the bulk compositionis not consistent with early crystallization of hibonite. Based onthis observation, Beckett and Stolper (1994) concluded thathibonite nucleated metastably. Simon et al. (1998) also discussedthe possible relict nature of hibonite: In spherule Y17-6, they

found very high enrichments of 26Mgn in the glass, whereas thehibonites are devoid of it, and the bulk composition is spinel-saturated.

Inclusion 1476/124 studied here is also spinel-saturated(Fig. 6a), and its average hibonite/glass partition coefficient forTi (�1.1) conforms to the experimentally determined values of0.8–2.1 (Beckett and Stolper, 1994). When the bulk composition isprojected from TiO2 and hibonite onto the plane gehlenite–anorthite–spinel (Fig. 6b), it plots well below the hibonitesaturation surface, indicating that hibonite was not acrystallizing phase. Also from the projection scheme (Fig. 6b)we find that 1476/124 has a bulk composition similar to otherhibonite–pyroxene spherules. In the spinel projection onto theanorthite–gehlenite–forsterite ternary (Fig. 6a), the crystallizingphases in equilibrium are anorthite followed by melilite andfinally clinopyroxene. Most probably the present mineralassemblage is due to disequilibrium crystallization during fastcooling which suppressed anorthite and melilite crystallization.Such metastable crystallization of fassaite was observed byBeckett and Stolper (1994) in their experiments on silicatemelts at relatively high cooling rates. The hibonites must havecrystallized metastably over earlier formed hibonite seeds due tothe incomplete melting of the precursors. This is also supportedby the texture of the hibonite laths which have very tiny Ca- andTi-rich (most probably perovskite) particles in their cores whichcould not have crystallized from the liquid (Fig. 5a in Rout andBischoff, 2008). Thus, the perovskite- and hibonite-bearing relictsare metastably overgrown by hibonite from the melt. Beckett andStolper (1994) showed, from phase assemblage analysis, that theprecursor of the hibonite–pyroxene spherules is a mixture ofhibonite, spinel, melilite, and perovskite which was heated up to�1500–1600 1C.

The other two spinel- and fassaite-bearing spherules studiedare relatively FeO-rich (Table 2) and the CMAS projection schemeis not valid for inferring their crystallization history (Beckett et al.,

Fig. 6. Bulk compositions of the fassaite-rich spherules studied here projected onto relevant ternary plots of the CaO–MgO–Al2O3–SiO2 system. (a) Projection from spinel

onto the plane Anorthite–Gehlenite–Forsterite (Stolper, 1982; Beckett and Stolper, 1994). The FeO content of 1476/124 is low (0.42%). Thus, the effect is insignificant in the

CMAS analysis, but the other two inclusions (753B/14 and Dfr/23) have high FeO values. These two inclusions were also projected from spinel ignoring the FeO component.

Inclusions 753B/14 and Dfr/23 were further projected from spinel and hercynite onto the plane Anorthite–Gehlenite–Forsterite, assuming that all the FeO in the bulk is due

to the hercynitic component in spinel. The changes in position of these two inclusions in the ternary plane, after they were projected from spinel+hercynite are indicated

by arrows. Numbers in brackets are the spinel coordinates of the spherules, and the contours are those of the spinel saturation surface. A point, whose spinel coordinate is

higher than the contoured surface have spinel on the liquidus. (b) Bulk composition of the hibonite bearing fassaite-rich spherule 1476/124 (filled square), projected from

hibonite onto the plane Spinel–Gehlenite–Anorthite (Beckett and Stolper, 1994). The open squares represent the bulk composition of hibonite-rich inclusions and hibonite-

pyroxene spherules from other chondritic groups (Beckett and Stolper, 1994). Numbers next to the squares are the hibonite coordinates for the inclusions. Shaded areas

represent regions with no stable hibonite-saturated liquid.

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2006). To minimize the effect of high FeO, these inclusions wereprojected from spinel and hercynite. Here we assume that all theFeO is from hercynite in spinel and the initial liquid was iron-free.Thus, by projecting from hercynite we are supposing that theentire hercynitic component was earlier MgAl2O4 (John R. Beckett,per. comm.). This is clearly the case for inclusion 753B/14, but notfor Dfr/23, as it contains a complex Fe, Ti, Cr-oxide and fayaliticolivines (Fig. 5b in Rout and Bischoff, 2008). Inclusion 753B/14plots above the spinel saturation surface (Fig. 6a), and thisinclusion contains a large spinel crystal. According to the phasediagram, the crystallization sequence should be spinel–anorthite–pyroxene, but this does not agree with the actually observedmineral assemblage. Rapid cooling of the spherule must haveresulted in disequilibrium crystallization of fassaite and suppres-sion of anorthite crystallization as described above for thehibonite-bearing fassaite-rich spherule.

Formation of Al-rich chondrules and their precursors

Most of the Al-rich chondrules in R chondrites have high bulkFeO. This is either related to the highly oxidizing environment inwhich the R chondrite components formed or due to secondaryprocesses during metamorphism on the meteorite parent body.Based on their textures, Al-rich chondrules clearly formed asindependent, freely-floating, molten droplets and cooled ratherrapidly, similar to the formation of Al-rich chondrules in ordinarychondrites (Bischoff and Keil, 1983a, b, c, 1984). To infer thecrystallization histories of these objects, their bulk compositionswere projected from spinel onto the plane Ca2SiO4–Mg2SiO4–Al2O3 (Fig. 7a). Although this plot is applicable for refractoryinclusions which are spinel-saturated, all inclusions were plottedin the ternary diagram to compare them with other Al-richchondrules from different chondrites. Because of the

Fig. 7. Bulk compositions of Al-rich chondrules projected onto different ternary planes in the CaO–MgO–Al2O3–SiO2 (CMAS) system. (a) All Al-rich chondrules from R

chondrites projected from spinel onto the plane Ca2SiO4 (Larnite)–Mg2SiO4 (Forsterite)–Al2O3 (Corundum). Values in brackets are the spinel coordinates of the Al-rich

chondrules, calculated only for those chondrules with low oligoclase. Al-rich chondrules represented by filled squares plot above the spinel saturation surface. The different

inclusions can be represented by their spinel coordinates as: 2446/71B (�150); DfrB/32 (�133); 1476/22 (�113); 2446D/71 (�132); 753C/21 (�112); 2446C/51 (�116);

2446/85 (�54); 1476/74 (�73); DfrB/12 (�94). The inset shows the magnified portion of the ternary diagram, where all the chondrules plot. (b) Projection of the bulk

composition of DfrB/12 (25) and 2446/71B (�16) from forsterite onto the plane Tridymite–Diopside–Spinel. Numbers in brackets near the projected points indicate the

forsterite coordinates. Also shown are the contours of the forsterite saturation surfaces. Chondrules whose forsterite coordinate is higher than the contoured surface will

have forsterite as its liquidus phase. (c) Bulk composition of DfrB/12 (�50), and 2446/71B (32) projected from anorthite onto the plane tridymite–diopside–spinel. Number

in brackets show the anorthite coordinates for the chondrules; also shown are the contours of the anorthite saturation surfaces.

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exceptionally high FeO and Na2O contents of the Al-richchondrules (Table 2), this plot cannot be used to estimate theircrystallization sequence (e.g., Sheng et al., 1991; MacPherson andHuss, 2005; Beckett et al., 2006). The high FeO and Na2O contentsshift the boundary curves and the stability fields of thecomponents, thereby making estimation of the crystallizationprocess uncertain. However, the bulk compositions of Al-richchondrules in R chondrites are similar to those of the Al-richchondrules in ordinary and carbonaceous chondrites (e.g. Bischoffand Keil, 1983a, b, c, 1984; Bischoff et al., 1989; Sheng et al., 1991;Krot et al., 2002, 2004a; MacPherson and Huss, 2005; Tronche etal., 2007). Only four chondrules plot above the spinel saturationsurface (Fig. 7a) and all have high FeO and Na2O.

The three glass-rich chondrules (753C/21, 2446C/51, 1476/124;Fig. 7a) and two other chondrules, with only minor secondaryalteration plot below the spinel saturation surface in Fig. 7a. The bulkcompositions of these two chondrules were projected from forsterite(Fig. 7b) and anorthite (Fig. 7c) onto the plane tridymite–diopside–spinel (Sheng, 1992). In the forsterite projection, chondrule, DfrB/12(Fig. 2b) plots above the forsterite saturation surface and has low FeOand Na2O (Table 2). Chondrule 2446/71B (Fig. 2c) plots far below theforsterite saturation surface. For DfrB/12, which plots above theforsterite saturation surface and in the forsterite+spinel field, the firstphase to crystallize should be forsterite followed by spinel. Theresidual liquid will then move away from the spinel vertex until itmeets the spinel–anorthite boundary curve. At this point, spinelreacts with the liquid and plagioclase crystallizes. After spineldisappears, the liquid moves across the plagioclase field, wherediopside crystallizes and meets the diopside-anorthite boundarycurve. The residual liquid moves towards the diopside field and nottowards the proto-enstatite or the low-Ca pyroxene field, because ofthe higher Na2O contents of the crystallizing plagioclase (�An85–90).This plagioclase projects higher on the anorthite–albite joint and notonto the anorthite point in the ternary diagram. Thus, the thermaldivide, which is the intersection of the plane joining forsterite,plagioclase, and diopside with the spinel–anorthite boundary curve,moves to the right (Beckett et al., 2006). Consequently, the chondrulebulk composition plots to the left of the thermal divide and theresidual liquid moves away from the low-Ca pyroxene end and thecrystallizing plagioclase. This sequence of crystallization, as predictedby the phase diagram, is in agreement with the texture andpetrography of DfrB/12: It has a thick olivine rim and a coreconsisting of barred olivine grains in a matrix of anorthite andinterstitial fassaite (Fig. 2b).

The bulk composition of chondrule 2446/71B, which plotsbelow the forsterite saturation surface (Fig. 7b), was furtherprojected from anorthite onto the tridymite–diopside–spinelplane. Here, DfrB/12 which plotted above the forsterite saturationsurface, plots much below the anorthite saturation surface, inconfirmation with our previous results. Chondrule 2446/71B plotsslightly below the saturation surface (Fig. 7c) and, thus, the firstphase to crystallize can either be anorthite or forsterite. However,textural evidence suggests that forsterite was the first phase tocrystallize (Fig. 2c), and it was followed by anorthite and thendiopside. The crystallization sequence as predicted from thetextural studies is in agreement with the above prediction. In theBSE image (Fig. 2c) we see that the porphyritic olivine crystals areset in a mesostasis consisting of anorthite laths within a dendriticintergrowth of Al-diopside and anorthite. Thus, olivine crystalswould be the first to crystallize, followed by anorthite and finallydiopside from the residual liquid within the interstices.

The origin of the Al-rich chondrules and their relationship toferromagnesian chondrules and CAIs has been the topic ofconsiderable debate (e.g., Bischoff and Keil, 1983a, b, c, 1984;Bischoff et al., 1989; Sheng et al., 1991; Krot et al., 2002, 2004a;Krot and Keil, 2002; MacPherson and Huss, 2005; Tronche et al.,

2007). The first chondrule, in which evidence of extinct 26Al wasfound, is an Al-rich chondrule (e.g., Russell et al., 1996; Srinivasanet al., 2000; Hsu et al., 2003) and, thus, these chondrules provide avital link between the CAIs and ferromagnesian chondrules.Assuming closed system conditions, Tronche et al. (2007) useddynamic crystallization experiments of Al-rich chondrule analo-gue compositions to infer their crystallization history. They foundthat the thermal divide (line joining anorthite and forsterite in theCa2SiO4–Mg2SiO4–Al2O3 plot) and the anorthite–forsterite bound-ary curves play an important role in the crystallization of fourdifferent groups of Al-rich chondrules. From their dynamiccrystallization experiments they concluded that the Al-richchondrules attained peak temperatures of �1400–1500 1C andcooling rates of 50–500 1C/h. Krot et al. (2006) reported relict CAIsin 415% of the analyzed Al-rich chondrules in ordinary, enstatiteand carbonaceous chondrites, but only 5 found so far inferromagnesian chondrules. This observation and the highabundances of moderately volatile elements such as Mn, Cr, andSi in anorthite-rich chondrules shows that Al-rich chondrulesformed by melting of a mixture of ferromagnesian chondruleprecursors (olivine+pyroxene+Fe,Ni-metal) and anorthite–spinel-high-Ca pyroxene–forsterite bearing CAIs (e.g., Krot andKeil 2002; Krot et al. 2001, 2002, 2004a). Plotting the bulkcompositions of CAIs, Al-rich chondrules, and ferromagnesianchondrules in terms of Ca2SiO4–Mg2SiO4–Al2O3, MacPherson andHuss (2005) found that this plot defines a trend that closelymatches that predicted by equilibrium condensation processes.This was also supported by refractory and volatile trace and majorelement studies. This led them to suggest that volatility controlledgas-solid reactions lead to the formation of the Al-rich chondruleprecursors. Further, in this plot, the Al-rich chondrule composi-tional trend joins the type C CAI and the ferromagnesianchondrule compositions. From mixing calculations, MacPhersonand Huss (2005) estimated that a mixture of type C or plagioclase-pyroxene-rich CAIs and olivine-pyroxene-rich ferromagnesianchondrules can account for the bulk composition of the Al-richchondrules.

The bulk compositions of the least altered Al-rich chondrules(having no oligoclase) can only be used to guess at the precursormineral assemblage of the chondrules. The CaO vs. Al2O3 (Fig. 3a),TiO2 vs. Al2O3 (Fig. 5a), and CaO vs.TiO2, CaO vs. SiO2 (not shown)plots for these chondrules have positive correlations. They alsohave nearly cosmic Ti and Al ratios (Fig. 5a). However, MgO andNa2O are negatively correlated with Al2O3 (Fig. 5c). Thus, theprecursors must have had a refractory component rich in Ca, Al,Ti, and Si, and a moderately volatile to volatile-rich componentcontaining Mg, Si, Fe, and alkalis. Alternatively, one mightconsider crystallization of the molten precursor material in aMg-, Na-, Fe-, and alkali-rich environment formed due toevaporation of dust. Similar open system crystallization offerromagnesian chondrules was also proposed by differentauthors (Jones et al., 2005; Libourel et al., 2006). However,considering the refractory element concentrations, we suggestthat the precursors of the Al-rich chondrules in R chondrites had aCAI like component. Considering suggestions from earlierstudies (e.g., Krot and Keil, 2002; Krot et al. 2001, 2002, 2004a;MacPherson and Huss, 2005), the most likely mineral assemblagefor the refractory component is anorthite, spinel, andpyroxene. Based on our work, we have insufficient evidence tosuggest that melilite was not a constituent mineral of theprecursor refractory component. Considering closed systemcrystallization, the other precursor component has to be aforsterite/fayalitic olivine–pyroxene–albite (or nepheline) mix-ture. Fayalitic olivine must be a product of high temperaturemetasomatism of forsterite (Palme and Fegley, 1990). Some of thechondrules have cosmic Mg, Fe, and Si ratios (Figs. 3c, 5a, b), and

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this further suggests that the less refractory components of theprecursors were low temperature condensates with cosmicproportion of Mg, Si, and Fe, which was most probably olivine,pyroxene, and Na-rich plagioclase.

The three glass-rich chondrules probably formed from differentprecursor assemblages. These chondrules have very high MgO values(Table 2; Fig. 5b) consistent with their high olivine abundance. Theyplot in a completely different region compared to the other Al-richchondrules. Chondrule 753C/21 (Table 2) is rich in Na2O, K2O, and Cl,along with FeO, MgO but poor in CaO. Thus, the precursor must havehad a refractory component most probably rich in anorthite, low-Capyroxene, and spinel, which was later altered, perhaps due thereplacement of anorthite by nepheline/sodalite during reaction with aNa- and Cl-rich gas (e.g., Ikeda and Kimura, 1995; Kimura and Ikeda,1995). Another moderately volatile component must have beenfayalitic olivine to account for the higher FeO and MgO which musthave been incorporated during the metasomatism of forsterite byreaction with the same gas (Na-, Cl-, Fe-rich) that replaced theanorthite by nepheline (Palme and Fegley, 1990). Olivine must havebeen a dominant precursor as suggested by the high olivineabundance in the present inclusion. Chondrule 2446C/51 (Fig. 2d) isrich in Na2O, MgO, and FeO, but not in K2O and Cl. The CaO is higherthan in chondrule 753C/51, and MgO and SiO2 are similar to thelatter. A possible precursor assemblage may have been a refractorycomponent rich in Na-rich plagioclase (albite-andesine), nepheline,anorthite, high-Ca pyroxene, and spinel and a moderately volatileforsterite component. Again forsterite has to be a dominant precursorphase. Chondrule 1476/74 (Fig. 2e, f) is very high in forsteritic olivineand also has high Na2O and K2O, although lower than the other twochondrules. The precursor must have had higher proportions ofolivine and minor CAI-like components with abundant Na-richplagioclase/nepheline. After melting during chondrule formation,the three chondrules retained their glassy mesostasis, ruling outsevere metamorphic processing of these objects.

Alteration of CAIs in R chondrites

Most of the inclusions in R chondrites are heavily altered, bothby post-accretionary metamorphic processes and alteration in thenebular environment (Rout and Bischoff, 2008). The bulkcompositions of the altered inclusions show an enrichment ofalkalies (Na,K), halogens (Cl) and relatively volatile siderophileelements (Fe, Mn, Zn) (Table 2). As the R chondrites are highlyoxidized, having no metallic Fe,Ni in the matrix, and high Fa(Fa450) in matrix olivine in the primitive type 3 lithologies(Bischoff, 2000), the post-accretion metamorphism has intro-duced considerable amounts of Fe and Na into the CAIs. All theCAIs from the higher petrologic or metamorphosed lithologieshave dominant oligoclase produced during the metamorphicevent and highly hercynitic spinels. During this event, the FeOcontents of the inclusions increased along with ZnO. Due to theformation of abundant oligoclase in CAIs of the metamorphosed(type 4-6) lithologies, bulk SiO2 and Na2O probably also increasedand CaO decreased significantly (Fig. 3a, b, c). There is a positivelinear correlation between the Na2O and SiO2 contents of thecomplex spinel- and plagioclase-rich CAIs (Fig. 3c). Oligoclasemost probably formed by the decomposition of anorthite and/ornepheline and sodalite.

However, certain inclusions have been less affected by parentbody metamorphic events and still retain their pristine mineralassemblage (Fig. 3b). Nevertheless, these CAIs may have also beenaltered during some nebular processes. Metasomatic alterationdue to reaction with a solar gas can lead to the replacement ofmelilite by nepheline and sodalite, and perovskite by ilmenite(e.g., Allen et al., 1978; MacPherson et al., 1981; Wark, 1981; Krot

et al., 1995). The spinel- and Na,Al-alteration product-rich CAIsand most of the spinel- and fassaite-rich CAIs in the type 3lithologies have been significantly affected by metasomaticalteration in the solar nebula. During this process, CaO decreasedconsiderably, whereas Na2O, K2O, Cl, FeO, and SiO2 increased(Fig. 3a, b, c). During this process, perovskite was transformed toilmenite and spinels gained hercynitic components due to theintroduction of Fe (and Zn). Inclusions in the metamorphosedlithologies may also have been affected by nebular alterationprocesses, but the significant parent body metamorphism hasconcealed the nebular alteration effects. A nebular setting for themetasomatic alteration process is also favored by isotopic studiesof the CAIs. From the initial 26Al/27Al ratios in primary anorthiteand secondary sodalite in type B inclusions, Hutcheon andNewton (1981) and Davis et al. (1994) estimated that sodalitemust have formed 2.4 to 3.9 Myrs after anorthite formation. Faganet al. (2007) found canonical to very low initial 26Al/27Al ratios insecondary minerals in the Allende CAIs. Ushikubo et al. (2007a)studied the 36Cl–36S and 26Al–26Mg isotope systematics of amoderately altered type B2 CAI from Allende and found excess 36Sin sodalite and no excess of 26Mg in anorthite and sodalite. Theseobservations suggest that there were multiple episodes ofalteration processes starting from within 1.5 Myrs of CAI forma-tion to as late as 5.7 Myrs after (Lin et al., 2005; Fagan et al., 2007;Ushikubo et al., 2007a). Some of the fluffy, fine-grained andcomplex inclusions described above seem to have formed byagglomeration of mineral grains similar to those observed inordinary chondrites (Bischoff and Keil, 1983a, b, c, 1984). Bischoffand Keil (1983a, b, c, 1984) concluded that the irregularly shapedinclusions in ordinary chondrites formed by agglomeration ofrefractory dust and low temperature materials (rich in Fe, Na, andK), and subsequent secondary diffusion and reaction betweenhigh- and low-temperature components led to the formation oftheir mineral assemblage. Similarly altered inclusions have alsobeen studied by Grossman and Ganapathy (1975, 1976), Gross-man et al. (1975), Wark and Lovering (1977), and Wark (1979)who also proposed similar agglomeration to explain theirsimultaneous enrichment in refractory and volatile elements

The most pristine or least-altered inclusions have minor bulkvolatile elements like FeO, Na2O, and K2O (Fig. 3b). Some of thecomplex spinel- and fassaite-rich inclusions are also less alteredand they plot very close to the Ca/Al cosmic line (Fig. 3a). Aboveall most of the inclusions in R chondrite are heavily altered andpristine inclusions are rare.

Acknowledgments

We thank J. R. Beckett and H. C. Connolly, Jr. for theirconstructive reviews and personal communications, Jasper Berndtfor assistance in the microprobe work and Ulla Heitmann andThorsten Grund for technical support. This study is part of thedissertation of S. S. Rout at the Institut fur Planetologie(Westfalische Wilhelms-Universitat, Munster). This work waspartly supported by NASA grant NNX08AE08G (K. Keil, P.I.). This isHawaii Institute of Geophysics and Planetology publication #1814 and School of Ocean and Earth Science and Technologypublication # 7731.

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