GeochemicalJournal,Vol.26,pp.435to 446,1992

A n o ritic clast fro m t h e H e dj az c h o n d ritic b re ccia: im plic atio n s fo r m eltin g e v en ts in t h e e arly s olar syste m

K EIJI M ISAW Alt, SEIKO W ATANABE2, M ASAO KITAM URA2 N oBORU N AKAM URA3, K OSHI Y AMAM OT03 and A KIM ASA M ASUDA4~ Institute for Cosmic Ray Research, U niversity of Tokyo, 2-1, M idori-cho 3-chom e, Tanashi, Tokyo 1881 Departm ent of Geology and Mineralogy,Faculty of Science, Kyoto U niversity, Sakyo-ku, Kyoto 6062 Departm ent ofE arth Sciences, Faculty of Science, Kobe U niversity, N ada-ku, K obe 6573, and D epartm ent of Chem istry,Faculty of Science, U niversity of Tokyo, Bunkyo-ku, Tokyo 1 13, Japan4

(Received October 28. 1991; A ccepted N ovem ber 7. 1992)

A bundances of N a, M g, Al, K, Ca,Sc, Cr, Fe, Co, Ni, Rb, Sr, Ba, REE,Ir, and A u were deter- minedin aunique,noriticclastcarryinga fractionated REE com ponentfrom the Hedjaz(L)chondritic breccia byinstrum entalneutron activation analysis and isotopedilution m assspectrom etry.The clast, previously described by N akam ura et al. (1990), consists of tw o lithologies, and is depleted in siderophile and m oderately volatile lithophile elem ents w hen com pared with its host m eteorite. The REE abundancepattern oftheclastis L-chondritic(1.4-1.6x CI-)with alarge(620/0),Positive Eu anom aly. Strontium is also enriched (3.2 x CI-chondrite)relativeto trivalent REE. Chemical and petrologic data suggest that the elem ental fractionations observed in the H edjaz noritic clast could be accom plished in a single host-like with several episodes ofim pact m elting and heating. A n im pact m eltenrichedin feldsparcom ponentscould have been generatedin a neighboringregion on a parent body, and then infiltrated into the precursor m aterial ofthe clast. An enhancem entofplagiophileelem ents wouldthen be producedintheclast. M oderately volatileelem ent and siderophile elem ent fractionations could be related to gas/solid or gas/liquid pro cesses and silicate/m etalm eltfractionations,respectively,w hich m ay haveoccurred duringm elting and form ation ofthe clast.

calcic plagioclase have been identified in type-3 INTRODUCTION and 4 ordinary (H utchison and Lithic fragm ents with poikilitic, skeletal, G raham , 1975; G raham et al., 1976; Fodor and aphanitic, or m icroporphyritic textures in or- K eil, 1978; H utchison, 1982; H utchison et al., dinary chondrites provide im portant inform a- 1988; H utcheon and H utchison, 1989). O n the tion regarding the nature of regolith processes basis of the R E E patterns of glass and consti- and im pact events that took place on m eteorite tuent m inerals in the Bovedy and Sem arkona parent b odies (K eil, 1982; R ubin, 1985 and clasts, as w ell as the presence of 26M g excesses referencestherei n).In a few cases, clasts bearing due to in situ decay of the extinct radioisotope

Present addresses: tD epartment of A ntarctic M eteorites. N ationalInstitute of P olarR esearch. 9-10. K aga 1-chom e. Itabashi-ku. Tokyo 173. Japan tD epartment of Chemistry. University of Electro-C om m unications. Chofu. Tokyo 182. Japan

435

436 K. M isaw a et al.

26A1(tl/2= 7.2 x 105y),it has been suggested that planetary diferentiat ion m ust have begun at a v ery early stage ofthe solarsystem ,i.e., prior to the end of accretion of unequilibra ted ordinary chondrites and/or within a tim e scale com - parable to the m ean life of26A l (H utcheon and

H utchison,1989; H utcheon etal., 1989). Others have prop osed that these clasts w ere derived from m elt sheets within large im pact craters on their parent bodies (T aylor et al., 1979; K eil,

1982; R ubin, 1985; G rossm an and R ubin, 1986).

G rossm an an d R ubin (1986) described igneous Fig. 1. H edjazlight-colored, noriticclast atthesur- face of the slab (M useum d Histoire Naturelle No, clasts from the M anych (LL 3.4) and N gawi(L L 2132). It wasrep orted as clast11in N akam ura et al. 3.6) chondrites that show a sm o oth de crease in (1990). elem ent abundances with increasing volatility.

They concluded that the elem ental fractiona- tions observed in these clasts are consistent with were reported by M isaw a and N akam ura (1987) m elting of the host m eteorites. and N akam ura et al. (1990). In this w ork large

In this paper, w e report new results from the aliquots (1698 pg forisotope dilution and 153 pg petrographic and chem ical study of a noritic for IN A A) were used for analyses of trace and clast described by N akam ura et a l. (1990), and m ajor elem ents. discuss the im plications of these results fo r the C onstituent phases were identified using a origin ofthis t ype of clast. H itachi S-530 scanning electron m icroscope

(SEM ) equipped with a H oriba EM A X -2200 energy dispersive spectrom eter (E D S) and elec- EXPERIM ENTAL P ROCEDURES tron probe m icroanalyzers (E P M A; JE O L The H edjaz m eteorite is an L 3.7 chondrite m odels JX A-5A and JC X A-733). A n ac-

(Sears etal., 1980)thatis petrographically quite celerating voltage of 15-20 kV and a beam cur- heterogeneous (Kraut and Fredriksson, 1971; rent of I.5-12 nA w ere used. T he analytical data

Fredriksson et a/., 1986). The claststudied here w ere corrected according to Bence and A lbee w as found on a slab of the H edjaz specim en (1968) for E PM A analysis and to ZA F m ethod

(M useum d'H istoire N aturelle N o. 2132), and for SE M -E D S analysis. Bulk chem ical com posi- w as previously described as "fragm ent I" tions for m ajor elem ents w ere determ ined by

(M isaw a and N akam ura, 1987) and "clast II" com bining EP M A and SE M -E D S analyses of

( N akam ura et al., 1990). T he specim en is an in- constituent phases with m odal analysis. O ne of terior chip with a saw ed surface. B oth clast and the polished thin sections w as ion-thinned for its host m eteorite are very fresh and terrestrial transm ission electron m icroscopy. D islocation weathering efects seem negligible. A s show n in densities of olivine crystals in the foil w ere

Fig. I, t he clast is sub-rounded in shape m easured under a 200 kV transm ission electron

(- 3.5 x 2 m m in size and - 15 m g in total m icroscope (H itachi H -700). weight) and light-colored w hen com pared with The abundances of N a, Sc, Cr, Fe, Ni, Co, the host m aterial. A fter excavation by stainless lr, and A u were determined by instrum ental steel tools and ultrasonic cleaning in distilled neutron activation analysis (IN A A ), using essen- acetone, several chips w ere rem oved from the tiallythesam e procedure described by M isaw aet clast for chem ical analyses and petrographic ex- al. (1992). A bundances of M g, K, Ca, R b, Sr, am inations. A nalyiical results from sm all Ba, and R EE w ere determ ined by a m ass spec- fragm ents (chips Ila-e; 76-203 pg in w eight) trom etric isotope dilution (M SID ) technique

N oritic clast from the H edjaz chondritic breccia 437 following conventional cation exchange Shaw (T aylor et al., 1979),the angular fragm ent chem istry. L aboratory contam ination w as in N gawi (Fodor and Keil, 1978), and the lithic negligible and an analytical precision is con- fragm ent i n B ovedy (R ubin et al., 1981). sidered to be 1-20/0 (M isaw a and N akam ura, The clast has obscure contact relatio ns w ith

1988). thesurrounding m aterialand is heavily fractured

in lithology (II) (Figs. 2 and 3). W hile pyroxene

grain adjacentto the clastis highly def orm ed, a

RESULTS porphyri tic olivine-pyroxene does not

Petrograp hy and m ineralogy show deform ation (Fig.2a),indicating thatH ed-

A characteristic feature ofthe clastisitstex- jazis acom plex breccia.M ost olivine and pyrox- ture; itis dom inated by coarse-grained olivines, ene crystalsin the clast exhibitundulatory extinc- indicative ofsolidification from a m elt. The clast tion. D islocation densities of olivine crystals in consists of tw o lithologies. Lithology (1) con- the clast are uniform and of the order of 109 tains euhedralto subhedral olivine (100-200 pm cm ~2. T his rather high density has already been in size) and pyroxene (- 50 pm in size) crystals reported in olivine crystals in H edjaz by with granular textures, and interstitial A shw orth and Barber (1975). plagiocl ase (Fig. 2b). In lithology (II), skeletal O livine crystalsinthe clast are chem ically un- and elongate d olivine crystals up to 500p m long zoned and quite uniform (F a23),sim ilarto those and - 80 pm wide occu r with a parallel align - found in equilibrated L-group chondrites (Fig. m ent. T hese olivines show sim ultaneous extinc- 4a). Pigeonite (E n76Fsl6W 08),the next abundant tion w hen observed under cross-nicols. In- m ineral, is zoned (Fig. 4b) through subcalcic terstitial pyroxene and plagioclase also occur augite (En69Fsl5W 016) to augite (En54Fsl2W 034).

(Fig. 2c). A ccessory w hitlockite, apatite, il- M ost plagioclases in the clast are A n80-86 m enite, and chromite are pres ent. M inor A bl3-190 r0.7-1.1 in com position (Fig. 5a), in con- am ounts ofglass(< 10 pm in size) were observed trast with plagioclases in equilibrated ordinary in interstitial are as (Fi g. 2d) using SE M back- chondritesthat aretypically sodic(A n8.6_13.1;V an scattering electron im ages (BEIS). M etallic Schm us and Ribbe,1968). The calcic plagioclase n ick el-iron and troilite w ere not recognized in in the clast resem bles those observed in the the clast except as sm all nuggets in the veins of noritic clasts found in the H /L 3.6 Tieschitz olivine and py roxene grains. T hey are, how ever, (H utchison, 1982) and LL 3.0 Sem arkona (H ut- di stributed heterogeneou､lyin the host m eteorite cheon and H utchison, 1989) chondrites, as - 300 p m -sized globules(Fig. 2a). The m odes although the Sem arkona clast C C -1 contains no forlitho logy (1) are 75010 Olivine, 10 0/0 Pigeonite, glass.Interstitialglassesin the clast are depleted

9.40/0 Plagio clase, 50/0 augite, 0.50/0 W h itlockite, in C a, enrichedin N a(Table I and Fig.5b), and

and a trace of glass (0.10/0). Because of sam ple enriched in A lrelative to N a. They m ay be late- heterogeneity in lithology (II), w e did not deter- stage, residual m elts after the crystallization of

mine m od al abundance s of constituent phases. pla gioclase. W hitlockites occur as interstitial

SE M -BEI observations reveal that olivines are grai ns(50-100 pm in size), but apatiteisrare and

m o re abundantin lithology (II)than in lithology w as no t analyzed quantitatively. T here are no

(1). large system atic diferences betw een lithologies

Petrofabric m easurem ents show that the c- (1) and (II)in the chem ical com positions ofcon-

axes of olivines are aligned in lithology (II) but stituent phases.

not in lithology (1), su ggesting that oliv ines in

lith ol ogy (II) crystallized from a batch m elt. Elem ental abundances

Such a petrographic feature observed in In T able 2, a bulk chem ical com position

lithology (II) is sim ilar to the light-colored, calculated from lithology (1) is com pared with

vesicular r egion of the shock-m elted m eteorite the bulk chem ical com positions of sim ilar clasts

438 K. M isawa et al.

Fig. 2. SEM -BEIS Of a noritic clast and the H edjaz host., Ol: olivine, Px: pyroxene; Pl: plagioclase; W h: whitlockite, Ap: apatite; Gl:glass. (a) The H edjaz chondritic breccia (host) with alight-colored. noritic clast. The clastisem bedded in the brecciated hostthatincludesglass bearingferrom agnesian (e.g..Ieft). Brightestareasare m etallicFe-Niand sulfidesglobules.(b) Lithology (1):Enlarged view of centralpartof (a). E uhedralto subhedralolivineandpyroxenegrains with granulartextureare observed.Plagioclase occursin in- terstitial areas. (c) Lithology (II): Typicalskeletal or elongated olivine crystals are observed. Pyroxene and plagioclase occurin interstitialareas. Elongated olivinesexhibit coincidentalextinction. Petrofabric m easure- m entsshow thatthe c-axes of olivines are aligned.(d) Very minorsilica-alkali-rich glasses areidentlfied using SEM -BEIS. They representlate-stage. residualm elts aftercrystallization of plagioclase.

from N gawi (fragm ent N o. 6; Fodor and Keil, am ple, disagreem ents betw een the Cr, Ca, N a, 1978), M anych (M ensch-1; G rossm an and and K data obtained by diferent m ethods. This R ubin, 1986), and Sem arkona (C C-1; H utcheon is considered to be dueto sam ple heterogeneity. and H utchison, 1989), as w ell as with the H ow ever, the data selection does not afect the chem ical com positions (silicate portions) of the general feature of elem ental fractionation pat- H edjaz bulk m eteorite (Fredriksson et al., 1986) tern. Since the clastis sm all and heterogeneous, and m ean L-group chondrites. T he H edjaz clast it is not clear w hether the sam ples analyzed in m ost closely resem bles C C-1 from Sem arkona. this and in previous studies w ere taken from A sam ple of bulk clast, weighing 153 pg, w as lithology (1) or (II). analyzed by IN A A for som e trace and m ajor Figure 6 shows the C I-chondrite norm alized elem ents(T able3).In a coarse-grained rock such (re-norm alized to Si= 1.0) Iithophile and as the clast studied here, the data are likely siderophile elem ent abundances for the H edjaz afected bysam pling problem s.T here are,for ex- clast. T he elem ents are plotted in order of in-

N oritic clast from the H edjaz chondritic breccia 439

or ¥

20 20 (a) 10 10 Lithology(l)

80 90 Llthilogy(1) Ab 4-- An 80 90

or / 16 10 (b) Fig. 3. Opticalmicrograph (plane-polarizedlight)of athinsection of thenoriticclast,Iithology (II).H eavi- 8 e lyfractured region is observed (upper m ost). Olivines o e 5 ~~ show sim ultaneousextinction. LithotegyfuJ Lithology(1) Ab 8 16 - ﾖ･ An L*chondrites Ab 5 Io 20 Fig. 5. Chem ical com positions of (a) plagioclase (a) 15 29Olivines and (b) glassin the noritic clast. a*) o/oM.D.=1.5 JED 10 Z:: 5 creasing volatility from left to right. The R EE o data obtained for a large-sized sam ple (1698Ilg) 20 21 22 23 24 25 in this study are in good agreem ent with the Mo[eo/oFa m ean values for sm allsam ples (four chipsIlb-e; 75-200 pg) analyzed previously (N akam ura et car al., 1990). A highly fractionated R E E com po- 50 nent observed in chip Ila w as not recognized. 40 (b) j The R EE pattern ofthe clastis fiat(1.4-1.6 x CI- 30 chondrite) with a large, positive (620/0) E u 20 ~' anom aly, distinguishing it from patterns ob- 10 ~' tained from lithic fragm ents in ordinary chon- Mg lo zo 30 4) 50-7 Fe drites. The clasts from B ovedy and Plainview ex- hibit fiat R E E patterns with no E u anom aly (Keil Fig. 4. (a) H istogram s of Fa m ole o/o Of olivinesin et al., 1980; R ubin et al., 1981). T he R E E pat- the noriticclast.(b) Chem icalcompositions of pyrox- enein the noriticclast. Open and solid sym bolsrepre- tern of a pebble in B arw ellis fractionated w ith sentthechemicalcompositions of olivineorpyroxene light R E E-enriched, and a positive E u anom aly on lithology (1) and (II), respectively, (H utchison et al., 1988). The siderophile elem ents C o, Ni, Ir, and A u are depleted in the clastrelativeto L-group chon-

440 K. M isawa et al.

Table 1. Representative analyses of the constituentsphases of the H edjaz m eteoritel Hostmeteorite Oxide Noriticclast (wto/.) olin deform ed ol aug pig pl gl whit chr chondrule px Si02 37.8 51.8 54.2 46.4 68.4 O.05 0.05 38.0 55.6 Ti02 O.02 2.43 O.40 0.02 0.05 l.78 O.11 O.14 Al2 03 0.02 3.23 2.28 34~2 20.O 0.02 3.58 O.02 O.16 Cr2 03 O.04 1.10 0.95 O.04 O.04 58.3 0.07 O.13 F e O 21.2 7.53 11.l 0.19 0.56 1.31 29.4 21.7 12.4 Mn O 0.46 O.19 0.40 0.01 O.04 0.67 0.37 0.45 MgO 40.4 19.7 25.4 O.02 O.40 3.69 2.03 39.8 30.9 CaO O.02 15.0 5.64 17.8 0.94 45.2 0.08 O.04 0.23 Na2 O O.02 0.41 O.20 1.55 8.41 3,03 0.01 0.03 0.03 K20 0.01 O.11 0.01 O.04 1.OO O.03 0.01 0.01 O.04 P 205 47,l To tal 1OO lO1.5 lO0.6 100.3 99.8 100,4 96.6* 100.2 lOO.1 (m o leo/o)t En En An804 F0765 Fo?7.2 56.8 71 l En81.3 Fa22.8 Fs12.2 Fs17.5 Ab19.4 Fa23.5 Fsls.3 W o W o Or o.2 31.o II. 4 W o0.4 ｦol:olivine,aug:augite;pig:pigeonite,pl:plagioclase;gl:glass;whit:whitlockite;chr:chromite,px:pyroxene. * Including O.07010 V203- ~M olepercentforsterite(Fo).fayalite(Fa),enstatite(En),ferrosilite(Fs),wollastonite(W o),anorthite(A n).albite(Ab),and orthoclase(Or) end mem bers.

Table2. Com parison of the bulk chemicalcompositions of igneous clastsfrom H edjaz and LL-chondrites with the bulk compositions (silicatep ortions) of H edjaz and L-group chondrites

Oxide Hedjaz clast Ngawi Manych Sem arkona Hedjaz Average (wt"/o) lithology (1) No.6t M ensch-1$ CC-I､ bulkｦ L-chondrites* Si02 41.2 40.2 43.8 46.0 48.5 47.3 Ti02 O.16 O.13 O.1 0.2 0.19 O.18 Al203 3.6 6.0 3.8 4.2 1.96 2.74 Cr203 O.19 0.56 0.50 0.5 O.60 0.52 FeO 17.2 17.0 11.O 13.9 14.3 15.6 MnO 0.40 0.24 O.20 0.4 0.40 0.32 MgO 33.5 33.3 35.8 30.2 30.0 29.6 CaO 3.3 2.4 2.6 3.6 2.37 2.25 Na2O 0.29 0.08 0.21 l.18 1.04 K2O 0.02 O.06 O.02 O.13 0.17 P205 O.24 O.04 0.32 0.31 tFodorand Keil(1978). $Grossman and Rubin (]986). ､H utcheon and H utchison (1989). ｦSilicateportion.Recalculatedfrom Fredriksson etal. (1986). *Silicateportion.Recalculatedfrom Keil(1969).

drites;thisis consistentw ith the clast's depletion and is greater forlr. T he high C o/Niratiointhe of m etallic Fe-N i. Sim ilar fractionation of clast resem bles ratios from a K-rich fragm entin siderophile elem ents w asreported on alithicfrag- the B hola L L-chondrite (W lotzka et al., 1983) m ent from B ovedy (R ubin et al., 1981). T he and from chondrules with low siderophile depletion factor reaches about 100 tim es for N i elem ents from Sem arkona (Grossm an and

N oritic clastfrom the H edjaz chondritic breccia 441

Table 3. Com parison of results of chemicalanalyses rather than C V-chondritic, except for forthe H edjaz noritic clast with compositions of L- enrichm ents of plagiophile elem ents(A 1, Eu, C a, and CI-chondrites(valuesin ppm unless otherwisein- and Sr), Sc, Ti, and M g. dicated)

Hadjazclast* L-chondriteｦ CI-chondri tet DISCUSSION Na 3610d:250 6040-731O 4900 Sc 12.0:!:0.2 7.82-8.81 5.83 Form ation of the noritic clast Cr 3700ｱ93 3630-3940 2660 The dislocation densities ofolivine crystalsin

Fe('/.) 13.9+_O.8 20.3-22.7 18.51 H edjaz exceed the values 108 to 109cm ~2 Co 37.5:!:I.1 513-670 507 (A shw orth and Barber, 1975) and are the sam e Ni l20d:54 11200-13500 11OOO lr(ppb) 448-580 474 orders of m agnitude for those of olivines (- 109 notdetected Au(ppb) <40 142-171 145 cm ~2)in thenoritic claststudied here,suggesting

that the clast w as subjected to shock def orm a- M g("/･) 19.5 17-18 9.53 tion after its crystallization and incorporation , Ca(ｪ/･) 1.55 1.4-I.6 O.902 K 186 820-1200 566 into the ho st m e teorite. T he later shock efects

Rb 0.985 1.9-5.9 2.30 on the clast have erased the earliershock records Sr 24.8 10-15 7.80 for the clast.T herefore,itisim possibleto reveal Ba 4.24 4-6 2.34 La 0.403 0.34-0.50 0.253 the form ation process ofthe clast on the basis of

Ce 0.957 O.90-I.3 O.645 the physicalheterogeneity ofthe olivine crystals. Nd 0.710 0.65-0.92 0.476 The late shock (im pact) events responsible for Sm O.221 0.21-0.29 O.154 Eu high dislocation densityin olivines m ay have par- O.138 0.083-0.Il 0.0587 Gd 0.301 0.28-0.39 O.204 tially afected the texture of the clast, as in-

Dy 0.373 0.35-0.48 0.252 dicated in Fig. 3, but w ere not strong enough to Er 0.239 0.23-0.31 O.166 Yb 0.22-0.39 O.168 destroy the initial igneous texture, as found in 0.244 Lu 0.0407 0.034-0.046 0.0253 Fig. 2. T o consider the therm al history ofthe clast, *A bundancesofN a, Sc. Cr, Fe,Co,Ni,Ir.andA u werede- itisim portantto establishthe m axim um tem per- terminedbyINAA,andotherelementsby M SID throughca- tion exchangeresinseparation.ErrorsforINAA aredueto atures recorded in the clast. T he existence of

countingstatistics. pigeonitesuggeststhatthetem peraturecould ha- ｦDatafrom Kal!emeynetal.(1989),M asudaetal.(1973),De v e been at least as high as - 1200'C, even Laeter and H osie (]978). M inster and AIlegre (]979), Shimizu and M asuda (1986), and W asson and Kallemeyn though the clast w as not totally m elted. T he

(1988). petrofabric alignm ent of olivinesin lithology (II) tData from A nders and Grevesse (1990) and Nakamura suggeststhatth e clastw as heated at or abovethe (1974). liqu idus tem perature (- 1500'C), at least local-

ly. T he cool ing rate in the high tem perature

W asson, 1985). The fractionation trend of the range is not clearly determ ined: com par ed with

siderophile elem ents in the clastis considered to luna r norite,the clast m ust have cooled rapidly

be the result of elem ent partitioning betw een in order to preserve uninverted pigeonite. T he

silicate/m etal m elts follow ed by segregation of presence of glass in the clast dem ands fairly

m etal m elt. Chromium , M n, N a, K, and R b rapid cooling at tem peratures below - 1200'C .

abundances of the clast are 0.76, 0.86, 0.40, T he Fe/ (Fe+ M g)ratio of olivine in the clastis

0.18, and 0.23 x CI-chondrite, respectively. T he 0.23, in good agreem ent with the values of

gradual decrease in m oderately volatile elem ent olivines in I atm m elting experim ents on an L-

abundances with increasing volatility in the clast chondrite at 1200-1275'C at 10-14 atm P02

m ay be related to gas/Iiquid or gas/solid frac- (K ushiro and M ysen, 1979). Alternatively, the

tionation processes. A bundances of refractory c last m ay have been subsequently m etam orphos-

lithophile elem ents are nearly L-chondritic, ed with its host m eteorite.

442 K. M isawa etal.

2 2 D D D D D Lithophiles Siderophiles D D D I D D D D D D o 1 1 '1-. OlIlfII' I'D IlIllfIIll"If'l"O"II'l'ltIl:it'I"'fi]"D'tl'Iftl'lD't'tltIDL""] ~5 o o o o o o O ol :: D O O O O O o ,:,- * 0.5 D 0.5 _o Ior. Sc Lu Dy Nd La Yb Ca Ba Si Al Ti Er Gd Sm Ce Eu Sr Mg D D O II S ~; o H edlaz Clast o *J ~ co ~t ::) to' o' do :i: O L c h o n drite o o ca ~a) ~ L ~ ~ CE [] C V c h o n drite 4o*

0.1 o.1 Mn K Ir Co Au inoreasing volatility Cr Na Rb Ni Fe Fig. 6. The CI-chondrite (A nders and G revesse. 1989) norm alized (re-norm alized Si= 1.0) Iithophile and siderophile elem entalabundancesforthenoritic clastfrom H edjaz. Lithophileandsiderophileelem entsarear- ranged in the order of volatility from leftto right. D atafor C V chondrites arefrom Kallem eyn and W asson (1981) and W asson and K allem eyn (1988). D ata for L-group chondrites are from M asuda et al. (1973). D e Laeterand H osie(1978). M insterand All~gre(1979). Shimiz u and M asuda (1986). and Kallem eyn etal.(1989).

40 (a) Lithophile elem entfractionation A s show n in Fig. 7, C a positively correlates DO~ eo O~ with Sr and Eu in allclast chips(both correlation E coefi cients are 0.969; data for chips Ila-e and a Jn~] e ~ Il w hole-rock are from N akam ura et al., 1990). 20 Dnｩ , Elem entalcorrelations are not observed betw een , D~~ divalent cations and trivalent R E E. T he data ~tif.~}. 10 o points of w hole-rock sam ple do not plot on 0.18 regression lines, indicating that the correlation o[~e e (b) D~ ofplagiophile elem ents m ay not be dueto a post- o.16 crystallization, m etam orphic efects after the clast w as incorporated into the host m eteorite. - 0,14 GEL ll R ather, the correlation m ay be due to the a Du~ ~ 0.12 DU~l heterogeneous distribution of plagioclase in the clast.Ifthe abundances of C a, Sr, and E u in the 0.10 n~ clast are m ainly controlled by an am ount of ~F.~~. o.08 plagioclase, w e can estim ate Sr and E u contents 1.o I,2 1.4 1.6 1.8 2.0 of plagioclase. U sing alinearrelationship am ong ca('/') plagiophile elem ents and the C a content(12.70/0) Fig. 7. Strontium versus calcium (a) and europium of plagioclase (T able 1), w e obtain Sr= 310 ppm versus calcium (b)for six chips (data of chips Ila-e and E u = I.35 ppm ,in good agreem ent with the and whole-rock sam ple are from N akam ura et al., 1990)from the noritic clast. Strontium and europium B ovedy glass values of Sr= 365d:90 ppm , are positively correlated with calcium (both correla- Eu = 1.35:!:0.1 ppm , and Ca = 12.80/0 (Graham tion coefi cients of these elem ents are 0.969) in all et al., 1976). T his suggeststhatsim ilar precursor chips of the clast. and solid/liquid fractionation processes prevail-

N oritic clastfrom the H edjaz chondritic breccia 443

Nebularcomponent (GroupllREE) Accretion Fe- Ni-S Ioss? Moder ately volatileelem entsloss? L-chondriticm aterial

~(~* a) o> Feldsparcomponent IcsV ,~'l Fe-Ni-SIoss? ~o~, Partiaimelting Moderatelyvolatile elementsloss ec5

Noritic clast

Im pactevents Brecdation Fracturtng

Hed]azparentbody

Fig. 8. Proposed history of the H edjaz noritic clast. ed during the form ation of plagioclase in the then infiltratinginto a neighboring source region H edjaz noritic clast and C a-rich glassinclusions of this clast, enhancing the plagiophile elem ent in B ovedy. T hechem icalevidence argues convin- contentsin the clast source. M elt pockets found cingly for a planetary, rather than nebular, in ordinary chondrites are likely to have form ed origin for the noritic clast. T hus, a highly frac- by shocks with peak pressurein excess of 20-25 tionated R E E com ponent observed in chip Ila G Pa(St6fl eretal.,1988),and are usually enrich- (N akam ura et al., 1990) might com e from an ed in feldspar com ponent and depleted in m afic unm elted portion inherited from a prim itive com ponentrelativeto the hostchondrites(D odd nebular com ponent. D avis and Prinz (1989) also and Jarosewich, 1979). Since solid/liquid parti- reported a highly fractionated (G roup II) R EE tioning coefi cients of trivalent R E E for pattern for a feldspar-rich m elt clast from the plagioclase are sm all (Schnetzler and P hilpotts, Nilpena polym ict and suggested that a 1970), absolute abundances and a general pat- nebular RE E com ponent had been incorporated tern of R E E forthe clast m ight be unafected by into the m elt clast. an addition of this com ponent. A lternatively, O ne of the possible explanations for E u- and Sr-bearing phases (plagioclase) could enrichm ents ofE u and Sristhatthe clastisderiv- have form ed and been hom ogeneously ed from a partial m eltresidue.If w e assum e par- distributed during therm al m etam orphism on a tial m elting of 2.5-3 x chondritic m aterial, a C V-1ike grandparent body (N akam ura et al., light R EE-depleted (La/Lu.orwa ti.'d< 1) m elt 1990). T he positive anom alies of Sr and E u m ay residue with a positive Eu anom aly is produced. also be due to sam pling of greater am ounts of T his m odel cannot be applied to the unfrac- olivine and low -C a pyroxene. tionated R EE pattern (L a/Lu~or~'ti"d= ~ 1) of T he gradual decrease in m oderately volatile the clast. W e proposethatim pact m elting occur- elem ent abundances with increasing volatility red on an L-group chondrite parent body, with (Fig. 6), w hich is also observed in the Bovedy im pact m elts, enriched in feldspar com ponent, lithic fragm ent(R ubin etal., 1981),isnotconsis-

444 K. M isaw a et al.

tent with fractional crystallization processes. sulfide during m elting event (G rossm an and

M oreover, a low K /La ratio (ｲ 500) of the clast W asson, 1985) or depleted in Fe-Ni-S com po- relativeto ones of H edjaz hos t(K /La= 2240) as nent due to nebular fractionation (G ooding et w ell as ordinary and CI-chondrites can not b e al., 1980). due to any solid/liquid fractionations w hich T he partition coefi cient ofsilicate/m etalliq- took place in ordina ry or C I-chondrite parent uids for C o is one order of m agnitude larger bodies (Wa nke, 1975). Because partial m elts are than that of N i(D c.= 7.7 x 10-3, D Ni= 2 x 10-4; typically enriched in incom patible elem ents such Jones and D rake, 1986). D uring the m elting as N a, K, and R b, the sim ple infiltration event,the partitioning ofsiderophileelem entsbe- m echanism cannot explain the depletion of tw een silicate and m etal m elts m ay have occur- alkalisin the clast unless neighboring regions of red,withthe m etalm elts,enrichedin siderophile the clast had already been depleted in alkalis; elem ents, draw n aw ay from the parent m aterial this requires further heating events. It m ust be ofthe clast. A Iarge C o/N ifractionation w ould em phasized thatthe com position ofglass quoted then be produced in the clast. in T able I has norm ative corundum , indicati ng thatN a w aslostfrom residual m eltsby volatiliza- Source m aterial tion. T hus,w esuggestthatthe fractionation pat- T here are several sim ilarities betw een the tern for m oderately volatile elem entsin the clast noritic clast and chondrules (e.g., igneous tex- could be related to gas/solid or gas/liquid proc- ture, constituent phases,depletion ofsiderophile esses w hich occurred during m elt ing and fo rm a- elem ents, and existence of glass). H ow ever, w e tion ofthe clast. M inster and All~gre (1979) also distinguish the clast from ty pical chondrules by suggested that som e L-group chondrites lost R b itslarg ersize (atleast 2-3 m m in diam ete r),non- by volatilization during shock and reheating. If sphericalshape, and distributions of plagio phile vaporization of alkali elem ents occurred attem - elem ents. perature about 1000'C, abundances of refrac- In light of the m ore L-chondrite-like refrac- tory lithophile elem ents such as R E E might be tory/Si ratios in the clast and the sim ilarity of unchanged. Alternatively, m oderately volatile fractionation patterns of m oderately volatile elem ent fractionations m ay have occu rred dur- elem entsin the noritic claststudied h ere an d the ing nebular processes, prior to the m elting event lithic fragm entfrom Bovedy(R ubin et al.,19 81 ), ofthe clast(N akam ura et al., 1990). w e favor of an L-chondrite precursor. T he tw o

diferent lithologies (granular a nd ske let al tex-

Siderophile elem entfractionation tures) observed in this m m - scale clast m a y be

The clast is depleted in m etal and sulfide relate d to the diference of de gree of pa rtial along with siderophile elem ents relativeto chon- m elting. Thisis also consistent withthe exist ence driticlevels(Fig. 6). Theliquidustem perature of of a nebular (Group 11 R E E) c om pon entin the the Fe-Ni-S system for L-chondrite m aterial is clast. N evertheless, w e cannot rule out the about 1000"C (Takahashi, 1983). Iron-Ni-S possibility that the clast form ed b y shock-in- m elt does not readily segregate from residual duced m elting of an inhom ogeneous C V-like phases during partial m elting at tem perature precursor (N akam ura et a/., 1990). C om pared above the Fe-Ni-S Iiquidus (T akahashi, 1983, with ordinary chondrites (Bisch o f and K eil ,

W alker and A gee, 1988), T hus,the depletion of 1984) m ore abundant C A IS (i.e., fraction ated sulfides observed in the clast appears to favor a R E E com ponents) are d istr ib uted in ca r- m odel ofits form ation ascrystalline rock from a bonaceous chondrites. A n ad dition of

(nearly) com pletely m olten m aterial,rather than plagiophile elem ents either during im pact as m elt residue of chondritic m aterial. Alter- m elting on an L-chondritic parent body orby fo r- natively, the parent m aterials of the clast could m ation and distribution of plagioclase during be sim ilar to chondrules, w hich lost m etal and therm al m etam orphism on a C V-1ik e gr and-

N oritic clastfrom the H edjaz chondritic breccia 445 parent body, w hile possible, Ieaves unansw ered drules and inclusions in ordinary chondrites. the question of w hy the abundance of Ba in the N ature 303,588-592. Davis, A. M . and Prinz, M .(1989) Trace elem entsin cl astissi m ilarto the abundance oftrivalent R E E feldspathic clasts in polymict (abstr.) and also com parable to those in L-group chon- L unar Planet. Sci. X X, 222-223. drites.Itis ho ped thatsim ilar clasts willbeiden- De Laeter, J. R. and H osie, D. J.(1978) The abun- tified and studied in order to clarify both this dance of barium in stony m eteorites. Earth Planet po int a nd w hich processes are responsible forthe Sci. Lett. 38, 416-420. un ique texture and elem ental fractionation of D odd, R. T. and Jarosewich, E. (1979) Incipient m eltingin andshock classification ofL-groupchon- the clast. drites.Earth Planet. Sci.L ett. 44, 335-340. A possible history ofthe noritic clastissum - Fodor, R. V. and Keil, K. (1978) Catalog of lithic m ar ized in Fig. 8. A c cretion of parent m aterials, fragm entsin LL-group chondrites. Spec.Publ.N o. m etal/silicate fractionations, m oderately 19, U niv. of New M exico Inst. of M eteoritics. vola tile elem ent fractionations, and Fredriksson, K., Fredriksson, B. J. and Kraut, F. (1986) T he H edjaz m eteorite. M eteoritics 21, 159- enhancem ents of plagiophile elem ents could be 168. accom plished in a single L-chondritic parent G ooding, J. L., Keil, K., Fukuoka, T. and Schmitt, body with several episodes of heating and R. A. (1980) Elem ental abundancesin chondrules m elting, T his type of clast has only been ob- from unequilibrated chondrites:Evidenceforchon- served in a few type-3, chondrites. H owever, drule origin by m elting of pre-existing m aterials. Earth Planet. Sci. Lett. 50, 171-180. these clasts preserve a record of gas/solid frac- Graham , A. L., Easton, A. J., H utchison, R. and tionation process in the nebula and im pact Jerom e, D. Y. (1976) The Bovedy m eteorite; m elting events on the clast's parent body. m ineralchem istry and origin of Ca-rich glassinclu- sion. Geochim. Cosm ochim. A cta 40, 529-535. Acknowledgments- W ethank K.Yam akoshiforsup- Grossm an,J. N. and Rubin,A. E.(1986) The origin ofchondrules and clasts bearing calcic plagioclase portofthisstudyandinstructioninIN A A (forK.M .), and P. Pellas for providing us with the H edjaz in ordinary chondrites(abstr.). Lunar Planet. Sci. sam ples. W e are indebted to H. H onm a, E. X VII, 293-294. Takahashi,and T.Ishiifor use ofEPM As. This work Grossm an,J. N.and W asson,J.T.(1985) Theorigin w assupportedfrom thecooperativeprogram sprovid- and history ofthe m etaland sulfide com ponents of ed by the O cean Research Institute, U niversity of chondrules. G eochim. Cosm ochim. A cta 49, 925- Tokyo, the Institute of Study of Earth's Interior, 939. O kayam a U niversity, and the Institute for Atomic H utchison,R.(1982)M eteorites-evidencefortheinter- Energy,Rikkyo U niversity,and bya Grant-in-Aid for relationship of m aterialsin thesolarsystem of 4.55 Encouragem entofYoung Scientistsofthe M inistry of G a ago. Phys.E arth Planet.Int. 29,199-208. Education,Scienceand C ulture,Japan.W ethank M . H utchison, R.and Graham, A.L.(1975)Significance Kim ura, T. Tanaka,and an anonym ousreviewer for of calcium -rich diferentiates in chondritic theirconstructive com m entson an early version ofthe m eteorites.N ature 255, 471. m anuscript. H utchison, R., W illiam s, C. T., Din, V. K., Clayton, R. N.,Kirschbaum, C., Paul,R.L,and Lipschutz, M . E. (1988) A planetary, H-group pebble in the REFERENCES Barwell,L6,unshocked chondriticm eteorite.Earth Planet. Sci. Lett. 90, 105-118. Anders, E. and Grevesse, N. (1989) A bundances of H utcheon, I. D. and H utchlson, R. (1989) Evidence the elem ents: M eteoritic and solar. Geochim. from the Sem arkona for 26Al Cosm ochim.A cta 53, 197-214. heating ofsm ali planets.N ature 337, 238-241. Ashw orth, J. R. and Barber, D. J. (1975) Electron H utcheon, I. D., H utchison, R. and Kennedy, A. petrography of shock-deform ed olivine in stony (1989) M g isotopes and rare earth abundances in m eteorites.E arth Planet. Sci.L ett. 27, 43-50. plagioclase from ordinary chondrites: a search for Bence,A.E.andAlbee,A .L.(1968)Em piricalcorrec- 26Al(abstr.). Lunar Planet. Sci. X X, 434-435. tion factors for electron m icroanalysis of silicates Jones, J. H. and Drake, M . J. (1986) G eochem ical and oxides. J. Geol. 76, 382-403. constraints on core form ationin the Earth.N ature Bischof, A. and Keil, K. (1984) Ca, AI-rich chon- 322,221-228.

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