Moon and Earth : compositional differences inferred from siderophiles, volatiles, and alkalis in basalts

Moon and Earth: compositional differences inferred from siderophiles, volatiles, and alkalis in basalts RAINER WOLF and EDWARD ANDEKS Enrico

Fermi

Institute

and Department of Chemistry. Chicago. IL 60637, U.S.A.

University

of Chicago,

Abstract-We have compared RNAA analyses of 18 trace elements in 25 low-Ti lunar and IO terrestrial oceanic basalts. According to Ringwood and Kesson, the abundance ratio in basalts for most of these elements approximates the ratio in the two planets. V&tiles (Ag, Bi, Br, Cd, In. Sb, Sn, Tl, Zn) are depleted in lunar basalts by a nearly constant factor of 0.026 + 0.013, relative to terrestrial basal%. Given the differences in volatility among these elements, thts constancv is not consistent with models that derive the Moon’s volatiies from partial recondensation of the Earth’s mantle or from partial degassing of a captured body. It is consistent with models that derive planetary volatiles from a thin veneer (or a residuum) of C-chondrite material: apparently the Moon received only 2.VA, of the Earth’s endowment of such material per unit mass. Chalroyens (Se and Te) have virtually constant and identical abundances in lunar and terrestrial basal& probably reflecting saturation with Fe(S, Se, Te) in the source regions. Siderophiies show diverse trends. Ni is relatively abundant in lunar basalts (4 x 10s3 x Cl-chondrites), whereas Ir. Re, Ge, Au are depleted to 10-‘P10~5 x Cl. Except for Ir, these elements are consistently enriched in terrestrial basalts: Ni 3 x . Re 370 x, Ge 330 x1 Au 9 x This difference apparently reflects the presence of nickel-iron phase in the lunar mantle. which sequesters these metals. On Earth, where such metal is absent. these elements partition into the crust to a greater degree. Though no lunar mantle rock is known, an analogue is provided by the siderophiie-rich dunite 72417 (-0.1% metal) and the complementary, siderophile-poor troctolite 76535. The implied metal-siderophile distribution coefficients range from IO4 to IO’. and are consistent with available laboratory data. The evidence does not support the alternative explanation advanced by Ringwood-that Re was volatilized during the Moon’s formation, and is an incompatible element (like La or W4’) in igneous processes. Re is much more depleted than elements of far greater volatility: (ReiU),, 2 4 x IO-’ vs (Tl/U)c, = I.3 x 10m4, and Re does not correlate with La or other incompatibles. Heacy alkalis (K. Rb, Cs) show increasing depletion with atomic number. Cs/Rb ratios in lunar basalts, eucrites. and shergottites are 0.44, 0.36, and 0.65 x Cl. whereas the value for the bulk Earth is 0.15-0.26. These ratios fall within the range observed in LL and E6 chondrites. supporting the suggestion that the alkali depletion in planets, as in chondrites, was caused by localized remelting of nebular dust (= chondruie formation). Indeed, the small fractionation of K, Rb and Cs, despite their great differences in volatility, suggests that the planets, like the chondrites, formed from a mixture of depleted and undepleted material. not from a single, partially devolatilized material.

1. INTRODUCTION

ONE OF THE early findings of Apollo I 1 was the striking depletion of many siderophile and volatile elements in lunar basal&, compared to terrestrial basalts (GANAPATHY rt ul., 1970). This finding has been confirmed by later studies (ANDERS rf uL, 1972 ; LACL et al.. 1972: GANAPATHY cv al., 1973). and apparently reflects compositional differences between the two planets (GANAPATI-~Yet (I/.. 1970; GANAPATHY and ANDIZRS,1974; PAPIKE and BENCE. 197X). RIN~;WOODand KESSON(1977) have questioned the selective depletion of lunar basalts, however. Using data from a variety of sources, and reclassifying some siderophiles to volatiles or vice versa, they concluded that the siderophile element patterns in the two planets are quite similar after all, implying “that the Mom Eurth’s

wns derived core

,fkotn

thr

Earth’s

mmtle

@er

t/w

paper. extending a preliminary effort (WOLF rt al.. 1979a). Two sets of RNAA analyses from this laboratory are available: (I) 25 analyses of low-Ti mare basalts from Apollo 12 and 15, critically reevaluated by WOLF et (11.(197913). (2) 10 analyses of terrestrial oceanic basalts (LAL:L rr al., 1972; HERTOGEN ~‘t ul., 1980). They include 15 of the 28 elements reviewed by Ringwood and Kesson, as well as 3 others: Tc. Sn and Br. We shall also extend the comparison to the heavy alkali metals: K, Rb and fs. They are slightly but consistently fractionated from each other in lunar and terrestrial basalts. 2. RATA

BASE

Some deletions were made in the above data sets. for the following reasons.

was jbmrrd.”

It seems desirable to check this trend on a homogeneous body of data. We have done so in the present

Snrw~ure hmu~t.s. 14053. 1432 1,184, i B. 15256 and 60639.5. As shown by WOLF cr it/. (1979b). these basalts 2111

R. WOLF and E. ANIXRS

2112

form a distinctive population, of high U, Rb, Cs, Cd and In content. They were therefore excluded from the mare basalt average, and were included in plots only when they fit into the general mare basalt trend. Clusts. 15459,28, a pyroxenite clast from a highland breccla. has suspiciously high Ir, Re, Au and Ge contents, due either to slight (~4%) contamination with matrix or to its matic character. Sorl sepurate.Mare gabbro 12033,390, a single 14mg fragment separated from soil 12033. is high in Ni. Ge, and Zn (JANSSENS et al., 197X), but low in incompatibles (MA and SCHMITT, 1978). This sample is a single, petrographitally characterized chip, whose composition was at most slightly affected by its regolith residence. We have nonetheless deleted it, since Ringwood (discussion remarks during I I th Lunar and Planetary Science Conference, 1980) has urged that soil separates be rigorously excluded from basalt surveys, reversing his earlier stand that even composite, petrologically impure, soil separates be included in surveys of highland rocks (DELANO and RINGWOOD, 1978). Suspect Ir LYJ~UC,S. WOLF et u/. (1979b) rejected the oldest 7 Chicago Ir analyses of Apollo 12 basal&, as they were much higher than later values. Owing to a typographical error, only 5 of these 7 values were italicized in Table I of WOLF er ul. (1979b), and we have therefore deleted the remaining two. for basalts 12051 and 12065 (0.09 and GO.05 ppb Ir, respectively). Prculiur sump/es. Basalt 15065 consists of a normal, felsic. and an anomalous, mafic portion, represented by subsamples 5 and 41 (CANAPATHY er ul., 1973). The latter is high in Ir (0.144 vs 0.0054 ppb) and Re, but low in incompatibles and chalcogens. We have excluded its Ir and Re values from the mean in Table I, but have generally retained this sample in our plots, identifying it as ‘65m’ (= 15065 mafic). Mujor ccild mirror rlrments. Data for FeO, MgO. Cr and La were taken from the JSC Lunar data base. Terrcstriul

husults

Following HLKTOGEF;er ul. (I 980). we have excluded two anomalous Indian Ocean basalts from DSDP leg 24, site 238, for the following elements: Ir, OS, Re, Au, Pd, Se, Te, Ag, Br, Rb and Cs. Values for FeO. MgO, Cr and La were taken from the references given by HERTOGEN et ul. (1980). For 2 of the 3 samples measured by LAUL it ul. (1972), Re values were given by KIMUKA et al. (1974). An unpublished Ge value for- 1154 is 1.51 f 0.12 ppm (U. Krghenbiihl, private communication. 1973). Data for FeO. MgO, Cr and La were taken from the references in LA& rr al. (1972).

Cl-chondrlte KRAHENBUHL

data for normalization were taken from er u[. (1973), except Br = 3.96 ppm, ppb. Pd = 545 ppb, Ni = 1.03%,, and

OS = 540 Sn = 1.63 ppm.

3. MEAN

ABUNDANCES

Let us do the comparison with

mean

abundances

and

in two then

stages,

proceeding

starting to indi-

for some key elements. Figure I shows for 18 elements, compared to the RINGWOOI~KESSON (1977) averages. Numerical data are given in Table 1. As a measure of volatility, we have indicated temperatures for 50% condensation from a solar gas at 10m5 atm (WAI and WASSON, 1977. 1979; TAKAHASHI et al., 1978). To indicate the statistical significance of the differ-

vidual

data

our new

means

SIDEROPHILES AND VOLATILES IN LUNAR AND TERRESTRIALBASALTS Moon

Earth

-0

If 0

0

Re Ni Pd Au

~.. 4

*cc + cz ~~

Sb

833 K

Ge 759

K

St? 684

K

0

w -4

0

1468K

1665K 1256 K 1256K

1153K

+40

-----~

~4

Te 638 K? Ag 894 K Zn

684 K?

.%l 669 K

In

482 K

Br 500 K Cd 452 K Bi 451 K 1I,,,,, TI I 438 K, L

16"

1

IO-Abundoncel

lo-J Cl Chondrlles

10.'

I

Fig. 1. Abundance as a function of condensation temperature from a solar gas at P = 10. 5 atm. Chicago analyses agree fairly well with the averages of RINGWO~D and KESSON (1977) except for the first 6, rather involatile siderophiles, where the Chicago analyses tend to give lower abundances and larger differences between Earth and Moon. The abundance patterns for volatiles (last 8 elements) are remarkably similar, as shown by the parallelism of the curves. The Sn value for oceanic basalts is from SMITH and BURTON (1972). Cl values used for normalization are mainly from KR~HENR~HL rr uI. (1973).

ences, we have also plotted the new means on a loglog plot, with error bars representing 907: confidence limits (Fig. 2). The pattern reflects a combination of two processes: cosmochemical (= preplanetary) processes that determined the bulk composition of the planets, and geochemical (= planetary) processes that controlled the distribution of the elements within the planets. No single classification can fit both processes, but a simple subdivision into volatiles, siderophiles, and chalcogens (Fig. 2) sems to be a reasonable compromise. The dividing line between the first two is drawn at a nebular condensation temperature of 750K (except that Sb, with a poorly determined T, of 833K, is assigned to the volatiles), but essentially the same groupings result if (Cl-chondrite-normalized) abundance in lunar basalts is used as the criterion: all volatiles fall above 9 x 10m4. and all siderophiles (except Ni), below.

Moon fable

I. Mean abun~in~es in low-Ti lunar mare and terrestrial oceanic basalts* lnits

Element

I- PPb

OS

Ii-

P&‘b ix’b

Re Ni Pd AU Sb G.? Sn Se Te Ag Zn In Cd Bi Br Tl Rb cs u

F

Lunar Basalts 1.0102 +.0046

I

1

C1.0025 41 SO.41 0.027 0.76 4.6 45 120 2.9 0.94 0.99 0.60 1.99 0.23 13.9 0.34 0.84 38 175

* Luntrr bc~lt.s: analyses of low-Ti

2.0012 *13

+.003 t.44 r1.c t20 f16 t.5 C.18 ‘..I1 t.26 2.35 +.04 13.9 f.06 +.21 L4 f32

Averages

Basalts

SO.0038 0.019 0.93 121 SO.19 0.23 17 1510 1360 160 2.9 26

1; 0.026

PPm PPb PPb PPb PPb PPb PPh ppb mb Pm pE;b wb PPb f+‘b epb PPm PPb &‘Pb

[err.

2.016 i.37

255 c.10 +zo +!?o ?I10 $26

il.6

58 70 i6

72 129 7.0 200 11.8 2.9 32

ill i-9 f.8

2160 52.8 il.9 t23

110 +84

of

24

selected

mare basalts (WOLF et al., 1979b; see also Data base section of this paper).

Terrestrial and ocean

busaits: Averages of 10 ocean floor ridge basalts (LAUL et ul., 1972; HER-

TOC;EN rr (II., 1980; see also Data base section of this paper). Errors including Mgjor

are WY,, confidence limits of the mean, &he appropriate t-Factor.

trrrlds

The 8 volatiles at the bottom of Fig. 1 show the familiar. 30. #O-fold depletion in lunar basalts that had been noted by GANAPATI-IYrt al. (1970) and later authors. The new means agree well with the Ringwood-Kesson averages, except for minor changes at Bi and In. The 6 siderophiles at the top of Fig. 1, and the next 4 elements ISb, Ge. Se and Te). on the other hand. show no uniform trend, certainly not the ‘similarity’ of lunar and terrestrial patterns claimed by Ringwood and Kcsson. Re and Au still are much more abundant in terrestrial basalts (though our new data have reduced the difference for Au while enlarging that for Re). For OS and Pd. our upper limits* are more than an order of magnitude lower than the values chosen by Ringwood and Kesson, and it therefore seems that the close agreement found by them was illusory. For Ir. lunar basalts have come down by a factor of 7 and now lie slightly lower than terrestrial basalts. This change is due to deletion of 7 old analyses of Apollo 12 basalts (see Section 2), which are up to two orders of magnitude higher than later Chicago analyses, and were therefore rejected by WOLF et al. (1979b). Ringwood and Kesson, on the other hand, used only these high values, failing to include or mention later values of GANAPATHY et rtf. (1973) even though using other data from that paper. For Ni. a small but well-established difference has * The higher hmits for lunar basalts merely reflect lower analytical

sensitivity

at

the

time

these

samples

measured, and do not imply higher abundances Moon.

2113

and Earth

were

in the

appeared between the Earth and Moon. Rin~wood and Kesson obtained their close match by Procrustean methods, adopting 150 ppm as the putative mean Ni content of 33 low-Ti lunar basalts (p. 435). though the actual mean of r~/;{lbl‘~ Ni analyses is only 30 ppm and the range is 6-64 ppm (TAYLOR, 1979a). Elsewhere (p. 454) it turns out that RI~Y~w~~)II and KESSO~ (1977) acutally used not ~),CLIIIS but putative n~rzimmm Ni vafues for the most primitive hasalts: 200 ppm and 150 ppm for the Earth and Moon. However. the latter value applies not to a true basalt but to the Apollo I5 green glass, a material of atypically high degree of partial melting (> 50?[,) that shows a~~liorrn~ll enrichments in vofatiles and siderophiles from volcanic and/or meteoritic sources (Fig. 5 of GANAPATW et LI/., 1973; Cbrou rt al., 1975). The most primitive basalts proper, 13JO2and 12(x3(1.contain only 64 and SZ69 ppm Ni, respectively (TAYLOR, 1979a; WOLF et czi.. 1979b). DELANO and RINGWOOD (197X) reexamined the problem in greater detail, and again concluded that the Moon and the Earth’s upper mantle had ‘similar Ni abundances (i.e. well within a factor of 7)’ But no matter whether one uses maximum or mean Ni values. whether from the entire literature or only from the Chicago laboratory. terrestrial basalts arc consistently higher, by factors of 3.0-6.2 (Table 2). The Chicago means plotted in Figs I and 2 obviously are the most conservative choices. It thus appears that 3 of the 6 sid~roph~~es (Re, Au and Ni) are systematically lower in lunar than in terrestrial basalts (Fig. 9). Ir also is lower, but the 90% confidence limits overlap (Fig. 2, Table 1). OS and Pd are uncertain at present, but the close coherence of OS and Ir (HERTOGW and JANSSENS. 1977) sugpcsts that the trend for OS may be similar to that for Ir. Do bu~s(~l~~~ ubu~zdun~~s rqflrct pl~i~l~rur~ ~Jbli~zdun~~.~? One must ask, of course, to what extent the diffcrences between lunar and terrestrial basalts reflect differences in bulk composition of the two planets. ‘The two types of basalt are not truly eqtiiv~~lent. lunar basalts being derived from a rather primitive source region (WALKE~Ret al., 1975; PAPIK~ er (I/., 1976), whereas terrestrial oceanic basalts are derived from a region of the mantle that is distinctly depleted in highly incompatible elements, such as K. Rb. Ba. U and light REE (GAST, 196X; SUAW, 1979; WASSI:RTable 2. Nickel content

of terrestrial

a. DELANOand RINGWOOD (1978). b. HERT~GENrl (il. (1980). c. TAYI.OR(1979a). d.

WOLF

ef d.

(197%).

and lunar

basalts

R.

2114

WOLF

Terrestrial

and E. ASIERS

Bosalts

(abundance/Cl

)

Fig. 2. According to RINGWOOD and KESSON (1977). the abundance ratio in basal& for most elements plotted here approximates the abundance ratio in the two planets. Diagonal lines give the Moon/Earth ratio; error bars are 90% confidence limits. Among siderophiles Ni is slightly (3x) enriched in the Earth. whereas Au, Re. and Ge are strongly enriched (9-370x). This enrichment may reflect the absence of metal phase in the Earth’s upper mantle, permitting these siderophiles to partition into the crust. Volatiles are depleted in the Moon by a nearly constant factor of 0.026. This suggests that the Earth and Moon got their volatiles from a common (C-chondrite?) source. without subsequent loss or fractionation, but that the Moon received only l/40 the Earth’s endowment per unit mass.

HLJKGand DEPA~LO, 1979; ANDERSON, 1980). RINGand KESSON(1977) have discussed this problem in detail, and argue that for many elements, basaltic abundance ratios can nonetheless be equated to bulkplanet abundance ratios, as long as the two basalts formed by similar (and substantial) degrees of partial melting. Seventeen of the 18 elements in Figs I and 2 WOOD

the newly added Sn and Br) fall in this according to the criteria of RINCWWD and KESSON (1977) and only Tl needs a correction for prior fractionation of the oceanic basalt source region. Ringwood and Kesson normalize to U for this purpose. But such normalization is justified only if both planets have the same U abundance, and since

(including

category,

IC

Fig. 3. Four highly volatile elements are strongly depleted in lunar compared to terrestrral basalts, but show little dispersion and occur in Cl chondrite proportions. Inasmuch as these elements differ greatly in nebular condensation temperature (Ag 894K, Zn _ 684K. Cd 452K. and Bi 451 K) and mobility upon reheating. it appears that they are derived from C-chondrite-like material, and were not fractionated by thermal events during or after the Moon’s formation.

2115

Moon and Earth this does not appear to be the case (TAYLOR, 1979b), we did not normalize the data. The Moon/Earth difference actually‘& smaller for the unnormalized data: Tl,/Tl, = 0.035 vs 0.013, and so our failure to normalize Tl shifts it in Figs I and 2 in the direction favored by Ringwood and Kesson. For the strongly siderophile elements, another condition must be satisfied before their basaltic abundance ratios can be equated to whole planet ratios: nickel-iron must be present in both planetary mantles, or in rleifher. Ringwood and Kesson have assumed the latter, but we shall find it necessary to reexamine this problem in Sec. 6.

4. VOLATILES: Ag, Bi, Br, Cd, In, Sb, Sn, TI and Zn These 9 volatiles have remarkably similar abundance patterns in the Earth and Moon, as shown by the parallel tie lines in the bottom part of Fig. 1, and the nearly constant depletion factors in Fig. 2 (mean Moon/Earth ratio = 0.026 + 0.013). These depletion factors are very well defined for 6 of the 9 volatiles in Fig. 2, the exceptions being Br, Sb and Sn. Some authors doubt that a meaningful record can be extracted from volatile elements, because they are so easily volatilized during eruption, metamorphism, or impact. It is therefore instructive to look at 4 elements covering a wide range of volatility (Fig. 3). These elements span a 450” interval in nebular condensation temperature: Ag 894K, Zn -684K, Cd 452K, and Bi 451K. They also differ greatly in their mobility upon reheating, juding from heating experiments on terrestrial basalt BCR-1: Ag and Bi were retained to only 1’4 and 5-10°A after 1 week at lOOO”C, whereas Cd and Zn were retained to 55 and 70.907” (IKRAMUDDIN ef al.,1976). Despite these differences in volatility, the data in Fig. 3 cluster tightly, fall close to the Cl chondrite ratio. and give essentially similar values for the Moon/Earth ratio: Bi 0.033, Ag 0.032, Cd 0.015 and Zn 0.013. The clustering speaks against any secondary redistribution. The Cl-like proportions and constant MooniEarth ratio are expected for models that derive the highly volatile elements from a ‘thin veneer’ of C-chondrite-like material (ANDERS, 1968; TUREKIAN and CLARK, 1969; WASSO~\~.197 I ; GANAPATHY and ANDERS, 1974; ANDERS and OWEN, 1977; MORGAN et al.. 1978a; MORGAN and ANDERS, 1979). They are not expected for models that derive the Moon’s volatiles from partial recondensation of a vaporized Earth mantle (RINGWOOD and KESSON, 1977; BINDER, 1978), or partial degassing of captured bodies (KAULA, 1977: SMITH, 1977). Given the differences in volatility among these elements (T, = 43%894K. exclusive of Sb), and the narrow condensation range (AT from 0 * In the light of our trace element data (Figs 1 and 2) it is useful to differentiate these (anionic) congeners of S from other (mainly cationic) chalcophiles that are less closely related to S.

to 90% condensation is less than IOOK; LARIMER, 1967), one would expect complete loss of some volatiles and complete retention of others-not the constant depletion factor actually found (Fig. 2). This is still true if the loss occurred by devolatilization at 200&4OOO”C and 102-IO4 atm (BINDER, 1979). Under these conditions, chosen to allow partial loss of SiO and Mg (BINDER, 1979) all volatiles will be totally lost. And during any recondensation at a later stage, the volatiles will be strongly fractionated from each other, owing to the steepness and divergence of their vapor pressure curves. It is for this latter reason that volatilization tends to be an all-ornothing process. incapable of producing uniform depletions of a group of elements (LAKIMERand ANDERS. 1967). We cannot rule out the possibility that the similarity in depletion factors is accidental, differences in abundance being fortuitously compensated by differences in geochemical fractionation. However, following RINGWOOL)and KESSOX(1977). we shall accept the depletion factors at face value. as measures of bulk composition.

5. CHALCOGENS:

Se and Te*

These two elements have essentially constant abundances, identical in lunar and terrestrial basalts (Fig. 4)as well as eucrites (LAUL et al., 1972; MORGAN et al., 1978b) and KREEP basalts (WOLF et ul.. 1979b). The obvious explanation is saturation with Fe(S. Se, Te) before eruption (ANDERSON. 1974; WOLF et N/., 1979b; DANCKWERT~I et al., 1980). Apparently this

j

100

nrl

1

t Te

0.001

0.01

0.1 ppb

Fig. 4. Lunar and terrestrial basalts have nearly constant Se and Te contents, which suggests saturation with Fe(S, Se, Te) prior to eruption. Open circles: non-mare basalts.

R. WOLF and E. ANDERS

2116

phase is present in the source regions of all these basalts. Indeed, MYSEN and POPP (1978) have invoked suifide saturation, followed by loss of FeS during ascent, to explain the low Ni contents of tholeiitic basalts, which are only d l/3 the equilibrium value of 60@700 ppm. Mare basalts of atypically low Se content (15058 and 15065m; Fig. 4) also tend to have low U and Rb contents (Fig. 4, also Fig. 4 of WOLF et al., 1979b), which suggests that the reservoir of S and Se is too small to permit saturation at large degrees of partial melting. 6. SIDEROPHILES:

Ir,Ni,

Re, Ge, Au (OS, Pd)

Much of the controversy over siderophile elements in the Earth and Moon centers on the v~!ut~l~~yof certain siderophiles. Ringwood and his coworkers have contended that all true siderophiles (Ir, Ni, etc., as well as the chalcogens Se and Te, which they reclassified to siderophiies) have identical abundances in terrestrial and lunar basalts, whereas those ‘siderophiles’ that are more abundant in terrestrial basalts (Re, Au, Ge, etc.) actually are volatile, and hence became depleted in the Moon during its formation (RIN~WWD and KESSON, 1977; DELANO and RINGWOOD. 1978; RINGW~OD et nl., 1980). The Chicago group, on the other hand, has attributed these differences to the presence of metallic nickel-iron in the source regions of lunar but not terrestrial basalts (WOLF et al., 1979b). We shall therefore look closely at Ir and Ni, two

5oo:

U(ppb) -

lO

l l

m%’

O

100 r9

50$

,

//I/ IO

Fig.

/I

@ Ii!/

ONi: , OhmI

100

5. Ni content of lunar basalts show weak positive cor-

relations with MgO/(MgO + FeO) and Cr, but a weak negative correlation with U. These trends apparently refelct increasing degrees of partial melting, with increasing uptake of olivine and chromite.

siderophile elements pur excellence whose nonvolatility is conceded--in a rare expression of harmony-by the Canberra and Chicago groups. First, we shall see what other data correlate with Ir and Ni content, and what these correlations tell us about the behavior of these elements in basalt formation on the Earth and Moon. Next, we shall plot the ‘controversial’ siderophiles (Re. Au, Ge) against Ir, and try to explain the differences. Our discussion will be focused

mainly on lunar basal& though terrestrial oceanic basalts will often be included in the graphs for comparison (see HERTOGENet u/., 1980 for a discussion of terrestrial basalts). We shall limit ourselves to Chicago analyses (WOLF er ai., 1979b; LAUL et al.. 1972; HERT~GEN et it/., 1980; see Sec. 2). Unfortunately, Ni, U, Ge and Re were not measured in most of the older analyses, and the data for these elements are correspondingly more limited. Nickel

600~ 3000 600

0

7‘-

arld jr~~itinl

Nickel shows positive correlations with Cr and MgO/(MgO + FeO) (hereafter Mg*f, but a negative correlation with U (Fig. 5). These trends reflect increasing degrees of partial melting, with increasing uptake of (Ni- and Mg-rich) olivine and apparently chromite. Iridium correlates with Ni and hence also with Cr

Fig. 6. Ir correlates with Ni and hence also with Cr and U (positive and negative correlations, respectively). This suggests that both Ir and Ni reside in refractory host phases, which are not necessarily identical, however. Ohvine, chromite and nickel-iron are the main candidates.

Moon and Earth

2117 ai Au (ppbl

‘.

l

- = _ o : A 1Q - 0

Apollo12 APOLLO15 Non-mare Dunlte-100 Troctolite Terr Ocemc

I I 1/““‘I -.7 0

0

0

-1

,,I / ,I,,//! , , /l////i )001 001 0 1wb Fig. 7. In lunar basalts. Re, Ge, and Au approach Ir in degree of depletion, but in terrestrial basal@ these elements are lOI-lo3 x more abundant. The lunar trend may reflect the presence of nickel-iron in the lunar mantle. which sequesters noble metals. This idea is supported by two known analogues. Lunar dunite 77417 (triangles) indeed contains -0.17; metal with large amounts of siderophiles in about Cl proportions, whereas lunar troctolite 76535 (stars), which is apparently related to the dunite by fractional crystallization, has very low abundances of siderophiles, in or below the mare basalt range.

and U (Fig. 6), but within the limited statistics, not with Mg*. A similar Ir-Ni and Ir--Cr correlation has been found in the Great Lake tholeiitic dolerite sheet (GREENLAND and LOVERING,1966; GREENLAND,1971). In terrestrial rocks. these elements are located in 2-3 different minerals: Ni in olivine, Cr and Ir in chromite (GIJRELSet nl., 1971; AGIORGITISand WOLF, 1978), Ir also in sulfides such as chalcopyrite (GREENLAND, 1971). On the Moon, nickel-iron is an additional possibility for Ni and especially Ir. Let us try to account for the lunar Ni-Ir correlation in the light of Figs 5 and 6. The lunar Ni-Ir trend can be caused neither by retained metal (Ni is present as Ni’+, not Ni”, and Ni/Ir is - 100 x Cl) nor by progressive reduction (the more magnesian basalts have no less Ir than the less magnesian ones). More likely, this trend is due to refractory host phases, which are the last to melt in partial melting and the first to crystallize during ascent of the magma. This explanation is supported by the trends in Figs 5 and 6: low Ni and Ir correlate with high U {i.e. small degrees of partial melting), whereas high Ni and Ir correlate with low U but high Mg* and Cr (i.e. large degrees of partial melting, including the refractory host phases of Ni and Ir). These host phases are not identical for the two elements. Olivine is the principal host phase for Ni but not for Ir; chromite is a major carrier for Ir but not Ni; and only nickel-iron and perhaps some sulfides are carriers of both. The Ni-Ir correlation in Fig. 6 apparently reflects the common refractory nature, not an actual identity, of these phases. Ir in lunar basalts thus is a sensitive but complex fractionation index, reflecting the extent of partial melting as well as subsequent loss of up to three host phases. Rhenium, germanium, gold

In lunar basalts (mare and non-mare), these three

Ir in degree of depletion, as shown by the proximity of the data points to the Cl chondrite line (Fig. 7). In terrestrial basalts, they are l@lOOOx more abundant. Rhenium shows a fair correfation with Ir, which would be further improved if the Re- (and Au-) rich samples 12022 and 15597 were disregarded. Germanium shows a very slight correlation, based, however, mainly on two Apollo 12 samples (12021 and 12046) at the low end, which happen to have low Ni and high U contents (Fig. 6). Finally, Au shows no correlation at all. Let us try to interpret these trends, particularly the Earth-Moon differences. Rhenium. Given the nearly 400-fold difference between lunar and terrestrial basalt, the point of contention is which of the two is ‘normal’ and which is ‘anomalous.’ KIMURA rt al. (1974) found that Re (and Au) in lunar basalts have about the abundance expected from experimental distribution coefficients, but are overabundant in terrestrial basalts by 1-2 orders of magnitude. They attributed this overabundance to oxidative destruction of metal in the final stages of accretion, so that any siderophiles accreted after core formation remained trapped in the upper lithosphere. This idea is supported by recent work. The six platinum metals as well as Au and Re are present in the upper mantle in chondritic proportions, at a mean abundance of 4 1% Cl (THOU, 1978). But a detailed study shows that Au and Rep-the two elements enriched in the crust-actually are quite variable in individual mantle rocks (MORGANand WANDLESS, 1979; MORGANer al., 1980a). About one-third of the 20 samples analyzed have chondritic Re/Ir and Au/Ir ratios, whereas the remaining ones show pro-

elements approach

gressive depletions to 0.03-0.1 of the Cl ratio. Apparently all 8 elements were accreted in chondritic proportions, but whereas the Pt metals remained trapped in the upper mantle, Au and Re have tended to parti-

211X

R. WOLF and E. AND~RS

tion into the crust during mantle differentiation. Their

high abundances in terrestrial basalts (e.g. HERT~CEN ut d.. 1980) thus seem to reflect 2 processes peculiar to the Earth: substantial accretion of chondritic matter after core formation, and a sufficient abundance of water to destroy nickel-iron and to complex Re and Au (KIMLIRA et d., 1974; KEAYS and SCOTT, 1976). One or both processes must have been inhibited on the Moon. DELANOand RINC~WOOD (1978) have argued, however, that the shoe is on the other foot: terrestrial basalts are normal and lunar basal& are depleted. They suggest that Re is present as an oxidized species, Re4+, which ‘would behave as an incompatible element similar to W4 + . during magmatic processes.’ Normalizing the terrestrial and lunar data to the incompatible element La, which correlates well with W (WANKI:cr al., 1973). they conclude that the net depletion of tunar hasalts is only 12 x , not 200 x . They attribute this difference to volatilization of Re during formation on the Moon, citing the rather high volatility of ReO, (Tcuh,= 1363C at 1 atm).* This suggestion fails the test of a La-Re plot (Fig. 8). Alas. unlike W or other incompatible elements, Re does not correlate with La, and the mean (Cl-normalized) RejLa ratio is -4 x 10m6. much smaller than the W/La ratio (0.05) or analogous ratios for even the most volatile incompatibles (e.g. Tl/U = 1.3 x 10e4; WOLF et al., 1979b). It appears that Re on the Moon is neither volatile nor incompatible, but siderophile. It is dil~~cult to derive from this insight further clues to the (lunar) geochemistry of Re. In principle, the correlation with lr is ambiguous; as we saw from the Ir-Ni -Cr plots (Figs 5 and 6) such correlations need imply only similar melting points, not actual identity, of host phases. However, the slope of - I, and the closeness to the Cl ratio. suggest similar phases and distribution coefficients for the two elements. Since Re correlates with Au as well as Ir. nickel-iron is a plausible candidate. Gelmur~ium. In terrestrial rocks, Ge is remarkably constant (within 2 x ). owing to its diadochy with Si (GoL,~s~I~~~~T. 19.54: DE ARGQLLO and SCHJLLING, 1978). For lunar basalts the compilation of WOLF rt d. (I979b) gives a range of I5 x , but when clast 15459.28 and soil separate 12033,390 are deleted, the * In support of this suggestion, RINGWOODet al. (1980) report that some Re volatilizes at l3oo”C from synthetic lunar basalt that was buffered with NiGNiO. However, these experiments were done at unrealistically high Re concentrations ( - IV,,)and oxygen fugacities [lunar basalts lie below even the Fe-Fe0 buffer (Snro et (11., 1973) and though this in part reflects reaction with C and loss of S2 upon pressure decrease during eruption, even the original fo. lies well below that of the Ni ~NiO buffer]. In the experiments of KIhltJKAof ~1. (19743,where Re was present in trace concentrations of 7-35 ppb. and .fo, was buffered by Fe,,Ni,,,-Fe0 (SMITH t’t al.. 1970). no volatilization of Re was observed even at 15Oo”C,although Au began to volatilize at 1400 C (Kimura et trl., 1974; unpublished data).

t ,/

I

I

1

Illlll

0.001 0.01 Fig. 8. Contrary to the suggestion of RIXW~~D et al. (1980)that Re is a volatile incompatible element, Re does not correlate with incompatibles such as La and is more strongly depleted than even the most volatile incompatrbles: (Rep_&, = 4 x lo-“, compared to (Tl/U),, = 1.3 x IO-! It would seem that Re continues to ‘present the fission hypothesis with an extreme embarrassment’

(RINGWOOD et ul., 1980). range shrinks to 5 x (Fig. 7). The small range, contrasted with that of Ir, Re, Au, suggests that Ge has a more dependable substitutional relationship, with a host of more constant abundance and K,-perhaps again Si. Go/d. There is no correlation with Ir (Fig. 7). This is not surprising, as Au and Ir fractionate from each other in cosmochemical as well as geochemical processes (GOTFRIEDand GREENLAND,1972: KIMUKAet al., 1974; HERTOGENet al., 1977). The range for lunar basalts is somwhat greater than that for terrestrial basalts (16 x vs 7 x ), but this may not be significant, given the greater number of samples and lower abundance (hence greater susceptibility to contamination). Without the two most extreme samples, the range is 5X. Why are Ge und Au depleted in lwur hults’?

We are left with the question why these elements are so depleted in lunar basalts relative to terrestrial basal&-by factors of IO3 x and 10, respectively (Fig. 7). Volatility can’t be the answer, whether in the solar nebula or on the Moon itself. Both Ge and Au are an order of magnitude more depleted in lunar basalts than are elements of decidely lower condensation temperature (In, Br, Cd, Bi, Tl) or higher volatility in open-system reheating (Ag, Bi, Tl). Yet Ge and Au are less depleted than these volatile elements in both ordinary chondrites (WAI and WASSON,1977) and ultramafic nodules from the Earth’s mantle (MORGANet al., 1980a, b). This leaves the strongfy siderophile character of Ge and Au as the obvious alternative. Given the large metal-silicate distribution coefhcients of Ge and Au (WAI et al., 1968; KIMURAet al., I974), a small amount of metal phase in the source region of lunar basalts would suffice to sequester Re, Ge, and Au. Ringwood has repeatedly contended that mare basalts cannot have equilibrated with an irort-rich metal phase, but this statement evades the issue: estimates of fo, (e.g.

SMITHct rtl., 1970) show that an alloy of substantial

Moon

distribution coefficients lowing assumptions.

Ni content is needed, and the experiments of KIMURA er al. (1974) on a synthetic lunar basalt indeed show gives the right that a Fe,,NijO alloy simultaneously Ni content (30--50 ppm) and right Au content (~0. I A further clue comes from lunar dunite 72415-72418, found as a large clast in an Apollo 17 boulder. Of the two samples analyzed by HIGUCHI and MORGAN(1975), 724 I5 is very low in siderophiles (e.g. Ir = 0.0052 ppb) except Ni (149 ppm), whereas 72417 is high (Ir = 3.13 ppb, Au = 2.55 ppb, Ni = 411 ppm). These siderophiles are not meteoritic. as the samples, though crushed, are neither brecciated nor co~ltaminated with matrix, and show a siderophile element pattern unlike that of any lunar breccia. (In cluster analysis of 59 lunar rocks, 72417 was the last to join, at twice the amalgamation distance of the penultimate rock in the set, and in discriminant analysis it received zero probability of belonging to a meteorite group; HIGUCHI and MORGAN, 1975). Its metal composition (24.5-3 I Jo/:,Ni. I .3-2.2% Co, 0.4*).6% Cr; DVMEK rt al., 1975) is outside the range of meteorites and lunar breccias, but is remarkably close to the Ni content of 30% estimated for metal coexisting with mare basalts (SMITH et ul., 1970). The Rb-Sr age of the dunite, 4.55 + O.IOAE, indicates that it formed in the primary lunar differentiation (PAPANASTASSIOU and WASSERBURG,1975). Its age and the apparently shallow depth of origin (DYMEK er NI., 1975) suggest that it is a crustal cumulate, not mantle material ancestral to mare basal&. Nonetheless, it contains metal, like the postutated source rock of mare basal&, but unlike terrestrial ultramafics, and is therefore worth comparing with basal& We have plotted dunite 72417,l in Fig. 7 (open triangles), after dividing the abundances by 100 to move them into the basaltic range. Thus adjusted. the dunite points fall in the basaltic fields of Fig. 7, displaced somewhat toward lower (Re, Ge, Au),& ratios. Let us derive nominal metal/silicate distribution Ir

Distribution

Coefficients

Low-Ti Basalts, Mean Laboratory Abundances

3x105 -1O'a mb

for these elements,

on the fol-

(1) The metal content and composition of dunite 72417 typifies that of ultrabasic rocks formed in the primary differentiation of the Moon; specifically, the source rock of low-Ti basalts. (2) Abundances in basalts represent metal-silicate equilibrium. (3) The siderophiles in dunite metal are given by the difference between 72417,l and 72415,lO; the metal content of the former is 0. I:,<. [This value is based on the excess Ni in 72417, and a mean Ni content of 292, for the metal. It lies between the values of O.l7”i,, estimated by DYMEK et ul. (1975) from a point count, and 0.06”/,, based on the difference between the mean and lowest Ni contents of 9 samples analyzed by LAUL and SCHMITT(I 975)].

ppb).

Table 3. Metal-silicate

2119

and Earth

The results are given in Table 3, along with laboratory D’s The last 3 lines of the table list the abundances in basalts and two other pertinent rocks, to be discussed below. The data certainly look reasonable. The D values parallel the nobility of the metals. and are consistent with such laboratory data as are available. However, it remains to be shown that these D’s have any meaning, as they are based on two admittedly unrelated materials: mare basalts and dunite 72417. Some reassurance comes from the two highland rock types listed in Table 3: troctolite 76535 and average pristine highland rock (= PHR). Both have siderophile element contents within a factor of 2- 3 of average basalt, exceept for Au in 76535 and Ni in PHR. A detailed study (DYMEK et cd.. 1975) has shown that 76535 may be related to dunite 72417 by simple fractional crystallization, and although no such specific link has yet been demonstrated for PHR, there are at least two reasons to expect a relatio~~sh~p: its highland location and gross petrologic complementarity to ultramafics. coefficients

i I

Au

8x10' >2x104b m'b

based on dunite Ge

5x104 ~10~ c PPb

72417 metal

Re

4x104 >2x103 b ppb

!Ni

6x103 7~10~5

PPrn

Troctoli te 76535 cd) Low-Ti Basalt?, Pristine Highland Rock (e,f)

a. RAMMENSEE(1977). Tholeiitic basalt and olivine nephelinite. b. KIMURA et ul. (1974). Synthetic Apollo 11 basalt-Fe,oNi30. Phase separation was incomplete for this material, and the true D’s may actually be close to those for terrestrial basal& equilibrated with Fe,oNigo: Au = 3.3 x 10“ - 7 x 105; Re = 2.4 x lo4 - 8.9 x 105. c. WAI et al. (1968). Olivine (Fa,S-Fa,OQ) - Fe,oNi,o at 900°C. D rises steeply with temperature, and should be much higher at the basalt liquidus. d. MORGAN et a/. (1974). e. GROS et (11.(1976). A representative composition derived from 13-22 pristine rocks by regressions against Rb and Cs, for a nominal Rb content of 0.72 ppm. f. ANDERS (1978).

2120

R. WOLF and E. ANDERS

Razor leaves such a metal phase as the main possibility for the other two as well. It appears then that the low abundances of Re. Ge, Au in the lunar crust reflect sequestering by metal phase in the mantle, not volatilization during formation on the Moon. On Earth, such a metal phase is absent, assowing these elements to assert their lithophile character and in some cases to partition into the crust to a significant degree.

Thus there is strong reason to attribute the siderophile element pattern of troctolite 76535 to equilibration with a metal phase such as that in dunite 72417. For the other two rocks the evidence is more tenuous, as we have no samples of the complementary metal phase. Nonetheless, there are two arguments pointing to dunite metal or a close equivalent. First, dunite metal has a roughly chondritic siderophile element pattern (Fig. 7). like the Earth’s upper mantle (CHOU, 1978; MORGAN et al., 19XOa). Chondritic composition is a widespread. preferred pattern in the solar system, and since it is present in the ultrabasics sampled thus far from these two planets. and at about the same levels (0.5- OX?/, Cl for OS, Ir, Re Au), it seems likely that the unsampled regions of the lunar mantle also have essentially chondritic composition. Second, all three rocks in Table 3 have similar siderophile element patterns. Since one of these patterns (76535) apparently was derived from essentially chondritic metal in 72417, a light stroke of Occam’s

7. ALKALIS There is good evidence that alkalis are depleted in the Earth and especially in the Moon. K/U ratios for the two planets are 1 x lo4 (WASSERR~JRGrf u(., 1964) and 2 x lo3 (ELDRIDGE et (II., 1975 and earlier papers), compared to the Cl chondrite ratio of 7 x 104; Sr is less radiogenic than expected for a chondritic Rb/Sr ratio (GAST, 1960, 1972; HURLEY, 1968; PAPANASTASSIOUet ul., 1970); the Ar4’ content

l Lunar Llosoltr + Oceonlc*

Cont-

0 Earth,Emplrlcol 0 Earth,Theoretical + Eucrltes x Sherqottttes CHONDRITES oaof? C2 C3 LL E6

Abundance

0.1

(Cl

chondrltes:

I 1)

Figs 9a and 9b. Basaltic rocks (lunar and terrestrial basalts; eucrites and shergottites) tend to be progressively depleted in heavier alkalis, relative to Cl chondrites. Among chondrites, some LL’s and E6’s come close to matching the Rb/K and Cs!Rb ratios of (extraterrestrial) basalts. If these ratios are representative of the bulk planets. then the alkali depletion in these planets can. in prrnciple. be explained by remelting of nebular dust (= chondrule formation). Terrestrial oceanic basalts are more depleted than continental basalts, reflecting derivation from depleted mantle. Empirical models for the bulk Earth may be more representative, and overlap the chondritic range. Given the large differences in volatilities among heavy alkalis (GIBSON and HLRRAKI). 1971) the small fractionations actually observed suggest that the planets, like the chondrites. are mixtures of depleted and undepleted material, rather than partially devolatilired residua. Meteorite values were taken from GOLD (1971) and references cited therein, as well as various more recent studies. mcluding unpublished data from Chicago. Ocean ridge basalt data are regional averages, designated by the following letters: E = East Pacific Rise, G = Gorda Rise, J = Juan de Fuca Ridge (KAY ef uI., 1970); m = Mid-Atlantic Ridge, A = Azores (WHITE and SCHILLING, 1978): M = MidAtlantic Ridge (HART, 1976). F = FAMOUS area (WHITEand BRYAN,1977). Continental basalts are from FLANAGAN (1973): 1 = CRPG-BR, 2 = GSJ-JB-I, 3 = USGS-BCR-I, 4-USGS diabase W-l. Earth models are: G = CANAPATHY and ANDERS (1974) L = LARIMEK (1971). Sh = SHAW (1972) Sm = S~IITH (1977). Lunar basalt data for the RbK plot are from Gast, Hubbard, Nyquist and Rhodes (compilation by WIESMANN and HURBARD. 1975), whereas those for the Cs-Rb plot are from various Chicago papers (compilation by WOLF et al., 1979b). Cl chondrite values used for normalization were: K = 544ppm (NICHIPORUK and M~K)K~. 1974); Rb = 138 ppm, Cs = 192 ppb (KRAH~NBUHL Ctal., 1973).

2121

Moon and Earth of the Earth’s atmosphere points to a low abundance of K (GAST, 1968: HUKLEY, 1968; LARIMER, 1971); etc. Thus both the depletion relative to Cl chondrites, and the Earth--Moon difference, need to be accounted for. Some authors explain this depletion by ud hoc hightemperature processes during the formation of the planets. i.e. non-condensation or volatilization (RINGWOOD. 1966; KALLA, 1977; RINGWOOD and KESS~N, 1977). whereas others attribute it to chondrule formation (ANDERS, 1964; LAKIMER and ANDERS, 1967; GANAPATHY and ANIEKS, 1974). on the aSSumptiOn that this process-pervasive in the region of the meteorite parent bodies-was equally important in the region of the inner planets (WOOD, 1962, 1963). In the absence of more specific clues, it may be useful to compare alkali abundances in the Earth and Moon with those in chondrites. We consider only K, Rb and Cs, because Li and Na show little fractionation in chondrites (NI~HIF(~R~~~and MCIORE,1974). Because the fractionations are small, we limit ourselves to simultaneous analyses of two or more alkalis in the same sample. Such data are plentiful for basalts and eucrites. but not for chondrites: good K analyses are scarce and are rarely accompanied by analyses for other alkalis. The results are shown in Figs 9a and b, with the Cl chondrite ratio for reference. Chondrite classes showing little or no K/Rh fractionation are excluded. In both graphs, lunar and especially oceanic basal& fail below the Cl chondrite line, indicating a progrcssive depletion in heavier alkalis. The low RbK ratios of oceanic tholeiites are of course well known. and reflect their derivation from a depleted region of the mantle (GAST. 196X; SHAW, 1968, 1979; ANDERSON, 1980). Continental basalts have essentially unfractionated RbiK ratios, but are distinctly depleted in Cs, uith Cs!Rb ratios in the oceanic basalt range. (See HEKTOCXNuf ai.. 1980. for further discussion of the terrestrial data). Shergottites show only a slight depletion of Cs. whereas eucrites show substantial depletions in Cs and especially Rb. WC are once again faced with the task of recognizing ;1 nebular pattern in igneous rocks. This should not he too hard in the Cs-Rb plot (Fig. 9b), because both elements are very incompatible and fractionate very littlc in igneous processes (OKAMOTOPI ul.. 1975). Their ratios in cucrites. lunar basalts. and shergottites are nearly constant over a total range of - lo2 (mean values 0.36, 0.44 and 0.65, relative to Cl chondrites), and presumably represent the abundance ratios in the respective planets. In contrast, the Rb/K ratio differs markedly in these 3 groups (Fig. 9a), and is quite variable in aucrites. At least part of this variation mny be due to igneous processes, as on Earth (SHAW, 1968). We shall therefore base our argument mainly on Fig. Yb. The chondrites probably give a fair picture of the fractionations expected in chondrule formation, though at least for Cs it may be somewhat distorted

by thermal metamorphism (LL’s and H’s: SMALES et ffL, 1964; LAUL et ul., 1973; IKRAMUDDINrt a/.. 1977) and hydrothermal activity (C2’s: WOLF rt ul., 1980). The chondrite points in Fig. 9b show a fair spread for each class. This is to be expected, because chondrules are quite variable in composition (WALTER, 1969; OSBORN ut uf.. 1973). consistent with the highly localized, small-scale nature of the chondrule-fornli[lg process (WOOD, 1963). Among these chondrites, E6’s and some LL’s come closest to matching lunar basalts, eucrites, and shergottites. In Fig. 9a. too. the LL’s match lunar basalts very nicely, but in view of the motley nature of the chondrite data and the possibility of igneous fractionation of Rb and K. some reserve may be in order. It thus appears that chondrule formation. of the type experienced by LL- or E6 chondrites, might also account for the K-RbCs fractionation of the Moon and the eucrite and shergottite parent bodies. For the Earth, the situation is complicated by variable depletion of incompatibles from different parts of the mantle (WASSERBURGand DEPAOLO, 1979) and by alkali fractionations among crustal rocks. Empirical models that attempt to estimate global abundances from actual concentrations in major rock types (open diamonds in Fig. 9) consistently give Rb’K ratios near the Cl value, but Cs,Rb ratios a factor of 0.15~0.25 lower. The purely theoretical model of GANAPATHY and ANDERS (1974; hexagon in Fig. 9) assumes Cl ratios for both pairs of elements, but admits that this is a bad assumption for Cs and 5 other elements from the fringes of their respective volatility groups. It appears that the Earth is selectively depleted in Cs (see also HERT~GEN rt al., 1980. for discussion of this point). If the empirical models represent the true alkali content of the Earth, then the Earth has experienced a slightly more severe alkali depletion than did the chondrites. Both the absolute depletions and the Cs/Rb fractionation are somewhat greater than those observed in chondrites. As aficionados of Occam’s Razor, we prefer to believe that the same. chondruleforming process was responsible for all these patterns, and merely went somewhat farther for the Earth (and eucrites) than for the chondrites. Readers preferring the blunter implements in Occam’s household of course are free to devise altogether different, crcl IIOC processes for the alkali depletion on planets. Eyewitnesses to the formation of planets are scarce. as l_JRf:Y (private communication. 1960) pointed out long ago. Acknonlelillrm~,Irs-We thank M.-J. JAYXNS, J. H~KTOCXN,and H. PALMEfor permlssion to quote their data on oceanic basal@ and KATHLEENM. PIERSONand AI.ISON LAIRDfor preparation of the drawings. This work was supported m part by NASA Grant NGL 14-001-167. REFERENCES AGIORGITISG. and WOLF R. (1978) Aspects of osmium. ruthenium. and iridium contents in some Greek chromites. Chrvn. &JO/. 23, 267.-272.

R. WOLF and E. A~IXRS

2122 ANIXRS

E. (1964) Origin,

age. and composition

ites. Spucc Sci. Rev. 3, 583-l ANDERS

E. (1968)

Chemical

of meteor-

14. processes

in

the

early

solar

system. as inferred from meteorites. Ax. Chum. Rex 1. 2x9 298. AUIXRS E. (1978) Procrustean Science: indigenous sideroohiles in the lunar highlands. according to Delano and kingwood. Proc. Yth knur Sci. COU/. pi. I61 I X4. A\I)f.RS E. and OWI:N T. (1977) Mars and Earth: origin and abundance of volatiles. Sciwcr 198, 45.3 465. ANIXKS E.. GAwPArw R.. KLAUS R. R.. LAUL J. C. and MORC;A\ J. W. (1971) Volatile and sidcrophile elements In lunar rocks: comparison wth terrestrial and meteoritic hasalts. PUK. _‘tld Luwr SC!. Co$ pp. 102 I -1036. AULERSON A. T. (1974) Chlorine. sulfur. and water in magmas and oceans. Gcol. Sot. A~I. Bull. 85. I485 ~1492. A\DERSOU D. L. (1980) Hospots and the evolution of the mantle. Sciencr, in press. BINIIFR A. B. (I 97X) On fission and the devolatilization of a Moon of fission origin. Eurrlr Pltrwf. Sri. Lc~t. 41. 3X 1-~3X5. Bwijtk A. B. (1979) Devolatiliration mechanism for a moon of fission origin. Lunur Plurwt. S(,i. .Y. pp. I%1 24. CFIO~ C.-L. (197X) Fractionation of sidrrophile elements in the Earth’s upper mantle. Prw. Yfh LI~MU %i. Co~f. pp. 219 ‘30. CfroL. C.-L.. BOY~TON W. V., SC NDRf KG L. L. and WASSON J. T. (1975) Volatiles on the surface of Apollo I5 green glass and trace element distributions among Apollo 15 soils. Proc. 6th Luwr Sci. Corzf: pp. 1701~1727. DANC‘KWERTH P. A., HESS P. C. and RUH~RF~RV M. J. (1980) Aspects of S systematics in non-mare lunar basalts. Luwr Plowt. Sci. .%‘I. pp. 195-197. 01: AKC;OI.LO R. and SCHILLIYG J.-G. (1978) Ge-Si and Ga-AI fractfonation in Hawaiian volcanic rocks. Geochim. Co.smochim. Ac,ttr 42, 623-630. DIILANO J. W. and RI~GWOOII A. E. (I 978) Siderophile elements in the lunar highlands: nature of the indigenous component and implications for the origin of the moon Prw. Yth Lwiur Sci. Coti/. pp. I Ii l5Y. Dwf-K R. F.. ALBEI. A. L. and CHOIIOS A. A. (lY75) Comparative petrology of lunar cumulate rocks of possible primary origin: Dunite 72415. troctolitc 76535. norite 7X2.75. and anorthosite 62237. Proc. 6th Lwwr Sci. Corlf. pp. 301 341.

ELixxfIxt J. S., O‘K~LL~Y G. D. and NORTH~~T~ K. J. (I 975) Primordial and cosmogenic radionuchdes in Descartes studies

and Taurus-Littrow materials: extension of bv nondestructive ;‘-ra! spectrometry. Proc. 6th Luwr Scl. Co~f. pp. 1407~1418. FLA~AGAX F. J. (1973) 1972 values for international geochemical reference samples. Gcwhim Cosmochim. Actu 37. I I 89-m1200. GA\APATHY R.. and ANIXRS E. (1974) Bulk compositions of the Moon and Earth. estimated from meteorites. Prw. jth Lww SC,;. COU/. pp. I 1XI --I 206. CANAPATHY R.. K~AYS R. R.. LAUI. J. C. and ANIXRS E. (1970) Trace elements in Apollo I I lunar rocks: implicatfons for meteorite influx and origin of Moon. Proc. Alwllo I I Lwlur So. Cor$. Geochim. Cosmoc~/tim. Actu Suppl. I, I I 17~_l 147. GAYAPATHY R.. MORGAN J. W.. Kfc~ffn~fri~ffi. II. and

AhlxRS

E. (I9731

Ancient

meteoritic

components

in

lunar highland rocks: clues from tract elements in Apollo I5 and I6 samples. Proc. 4fh Lumrr SCi. CON/: pp. 113%1~6l. GAST P. W. (1960) Limitations on the composition of the upper mantle. J. G~wph~s. Rrs. 65, 1287 1297. GAST P. W. (1968) Upper mantle chemistry and evolution of the Earth’s crust. In The History of’rllc Eurth‘s Crlrst (cd. R. A. Phmney). pp. l-27. Princeton Univ. Press. CAST P. W. (1972) The chemical composition of the Earth, the Moon

and chondrltic

meteorites.

In

T/w

.l’rrtwk, of

rllr

Solid

Eurth

(ed.

E.

C.

Robertson).

pp.

19-40.

McGraw-Hill. GIBSO~L’E. K. Jr and HUBRARU N. J. (1973) How to lose Rb. K. and change the K/Rb ratio: an experimental study. Proc. 4th Lunur Sci. Comp. pp. 1263-l 273.

R.. MILLARD H. T., Dfsno~of’c;~ G. A. and BARTEL A. J. (1971) Neutron activation analysis for osmium.

GfJet.Ls

ruthenium. and iridium in some silicate rocks and rockformlng minerals. In Acflrutiojr Am~l!,ai.s ,U Groclwmistr~ tmd Co.snlo~hc,nIistr~ (eds A. 0. Brunfelt and E. Steinnes) pp. 35Y -370. Universitetsforlaget. Goi_twHMif)T V. M. (I 954) (;eorhc’,,~i\f~~,. 730 pp.. Oxford Univ. Press. GOLFS Ci. G. (1971) Potassium (IY). Rubidium (37). and Cesium (55). In Htr~U~ok o/ Elemtwtul 1hfmdtmcc~s in Meteorites (ed. B. Mason). pp. I49 169, 2X5-296. and 407-41 I. Gordon & Breach. GoTTFRIf II D. and GRf tNLAhl> L. P. (1972) Variation of iridium and gold m oceanic and continental basalts. Proc. -73th I/if. Gcwl. Coiyr.. Set 10. pp. I .35~-144. GRIXYLAUII L. P. (1971) Variation of irfdium in :I differentiated tholciitic dolerite. C;cw/l/rn Cr~woc+~,tl. .-lcru 35. 3 I9 222. GKf I Uf_A\I) L. and LOVLRI\G J. F. (I 960) Fractionation of Iluorinc. chlorine and other trace elements during differentiation of ;I tholeiitic magma. (;coc~/l/,u. Cowo~i~iw. A~lU30. 963 98’. GROS J.. TAKAHASfff H., Ht~r~c;tu J.. MoR(;A~ J. W. and Aul)f KS E. (1976) Composition of the projectiles that bombarded the lunar highlands. I’roc~. 7111 Lwur SU.

CO~I/..pp. 2403 2435. HAKT S. R. (1976) LIL-element gcochemistrj. leg 34 basalts. In Ijiiritrl Rrport.\ o/ fhr Dwp Srrr Drilliyq Projrc~t. 34 (eds R. S. Yeats. S. R. Hart ct (I/.), pp. 7X3-XX. U.S. Government Printing Office. HI RTO(;I u J. and JAUSXNS. M.-J. (I Y77) Is osrnlum chemfca1ly fractionated on the Moon’! Proc. X(/I Lwtrr .Qi. CO,l{. pp. 47 -52. HE.KTOCXu J.. JA\SSIX M.-J. and PAI.MI H. (19X0) Trace elements m ocean ridge basalt glasses: Implications for fractionatfons during mantle evolutfon and petrogenesis.

Geochim. Cosmochim.

Actu 44, 2 125-2143.

HERTOOC;EN J.. JANSSENS M.-J., TAKAHASHI H., PALME H. and ANDERS E. (1977) Lunar basms and craters: Evidence for systematic compositional changes of bombarding population. Proc. 8th Lunur Sci. Conf pp. l7-

45. HfC;wHI H. and MOKC;A\ J. W. (lY7.i) Ancient meteoritic component in Apollo I7 boulder?. Proc. 6th Lzmur %I. C/m/. pp. 1625~~165 I. HURLEY P. M. (1968) Absolute abundance and distribution of Rb, K. and Sr m the Earth. Gwc,/lit,l Coww~llir~~. AHU 32. 273 2X? and 1025 1030.

IKRA~MIIIII)fNM.. BI>Z C. M. and LIPS(.HfJTz M E. (1976) Thermal metamorphism of primitive meteorites. IV. Comparison with trends for ten trace elements in terrestrial basalt BCR-I heated at 500-1000 C. Proc. 7th Lwtrr %I. Co/~f: pp. 35 I Y-3533. tKKAM~lIfII1 M.. Bfxz C. M. and LIf’SC’HL Ti! M. E. (1977) Thermal metamorphism of prlmitivc metcorltcs. III. Ten trace elements m Krymka L-3 chondritc heated at 400 1000C. Grochir?~ Cosr,wc~/~ir,~. A<.ttr41. ?9i--10 1.

JAYSSIX M.-J.. PALMf. H.. H~KToc;~\

J.. AlroE KSON A. T. and Ahf)EKs E. (IY78) Meteoritic matwal m lunar highland samples from the Apollo I I and I? sites Proc,. Yth Lwltrr- P/a~c,t. %i. Cwzf.. pp. 15.?7-~I510. KAULAW. M. (1977) Mechamcal processes a&tine &fferentiation of protolunar material. In Socrr!-Am&&n

Confrwwcc OH Cosmochemi.str~ Plurwts (eds J. H. Pomeroq NASA SP-370. Office. KA) R.. H[.fwAKf)

of

the, :Lloor~ und rhr

and Y. J. pp. X05%81?. U.S. Govcrnmcnt N. J. and CAST P. W

Hubbard), Printing

(1970) Chemical

Moon characteristics and origin of oceanic ridge volcanic rocks. J. Geopiiys. Res. 75, 1585-1613. KEAYS R. R. and SCOTT R. B. (1976) Precious metais in ocean-ridge hasalts: implications for basalts as source rocks for gold mineralization. Econ. Geol. 71, 7055720. KIMURA K., LEWIS R. S. and ANDERS E. (1974) Distribut~oll of gold and rhenium between nickel-iron and silicate melts: implications for the abundance of sidetophile elements on the Earth and Moon. Geochim. Cosmochim. Actu 38, 683-701. KR;~HENB~~HL U., MORGAN J. W., GANAPATHY R. and ANDERS E. (1973) Abundance of 17 trace elements in carbonaceous chondrites. Geochim. Cosmochim. Acts 37, 1353- 1370. LARIMER J. W. (1967) Chemical fractionations in meteorites-1. Condensation of the elements. Grochim. Costnoc&n. Acta 31, 1215-1238. LARIMER J. W. (1971) Composition of the Earth: chondritic or achondritic? Geochim. Cosmochim. Acta 35, 769-786. LARIMER J. W. and ANUERS E. (1967) Chemical fractionations in meteorites--II. Abundance patterns and their interpretation. Geochim. Cosmochim. Actu 31, 1239 -I 270. LAUL J. C. and SCHMITT R. A. (1975) Dunite 72417: A chemical study and interpretation. Prof. 6tlz &mar Sci. Corrf., pp. 123 1-l 254. LAUL J. C., CANAPATHY R., ANDERS E. and MORGAN J. W. (1973) Chemical fractionations in meteorites---VI. Accretion temperatures of H-, LL-, and E-chondrites, from abundance of volatile trace elements. G~~~~~~~. Cosmochin?. Acts 36. 329-357. LAUL J. C., KEAYS R. R., GANAPATHY R., ANDERS E. and MORGAN J. W. (1972) Chemical fractionations in meteorites --V. Volatile and siderophile elements in achondrites and ocean ridge hasalts. Geochim. CQ.~~~~?~~I~I~. ilrra 36. 329.--345. MA M.-S. and SCHMITT R. A. (1978) Chemistry of I0085 fragments and Apollo I I basalts and breccias. Lunur Plunrt. Sci. IX. pp. 67X-6X0. MOKC~AU J. W. and A~~I~EKSE. (1979) Chemical composition of Mars. Grochim. Cosmothim. Aetu 43. 160-1610. MoR~;~N J. W. and WANDLESS G. A. (1979) Terrestrial upper mantle: siderophile and volatile trace element abundances. Lrci7crr Plunrr. Sci. X, pp. 855-857. MORGAN J. W., HERTOGEK J. and ANDERS E. (1978a) The Moon: Composition determined by nebular processes. Mor,n und Planrts 18, 4655478. MOR~~ANJ. W., HIG(JCHI H., TAKAHASHI H. and HEKTOGIX J. (1978b) A “chondritic” eucrite parent body: inference from trace elements. Geochim. Cosn~~~~~i~n.Acts 42, 27-38. MORGAN J. W., WA~VDLESSG. A., PETRIE R. K. and IRvihG A. J. (I 980a) Composition of the Earth’s upper mantle. I. Sidcrophile trace elements in ultramafic nodules. Trcto~10p~~~si~s~ in press. MORC;AN J. W., WANULESS G. A. and PETRIE R. K. (1980b) Earth’s upper mantle: Volatile element distribution and origm of sideropbile element content. Ltrriur Plunrt. Sci. XI. pp. 740741. MoR~;A~ J. W., GAUAPATH~ R., HIGL.~HI H.. KR;~HE~BL’HL U. and AP;IJERS E. (1974) Lunar basins: Tentative characterization of projectiles, from meteoritic elements in Apollo 17 boulders. Proc. 5th Lunur Sci. Con$ pp. 1703.-1737. MYSEN B. 0. and POPP R. K. (1978) Solubility of sulfur in silicate melts as a function of f(sZ) and silicate bulk composition at high pressures. Annual Report, 1977-78 (Grophysicd Laboratory, Carnegie Institution, Wushington D.C., pp. 709-713. NICHIPC~W W. and MOORE C. B. (1974) Lithium, sodium

and Earth

2123

and potassium abundances in carbonaceous chondrites. Ge~~h~m. C~smochim. Actn 38, 1691-1701. OKAMOTO K., NOHDA S., MASUDA Y. and MATSUMOTO T. (1975) Significance of cesium/rubidium ratios in volcanic rocks as exemplified by the Nohi rhyolite complex, Central Japan. Groekem. J. 9, 201-210. OSBOK”; T. W.. SMITH R. H. and SCHMITT R. A. (1973) Elemental composition of individual chondrufes from ordinary chondrites. Geochim. Cosmochim. Actu 37. I9099 1942. PAPANASTASSIOUD. A., WASSERBURGG. J. and BURNETT D. S. (1970) R b-Sr ages of lunar rocks from the Sea of Tranquiihty. Earth Planef. Sci. Left. 8, t-19. PAPANAS~ASSIOUD. A. and WASSERBUKGG. J. (I 975) Rb-Sr study of a lunar dunite and evidence for early lunar differentiates. Proc. 6th Lunar Sci. Conf: pp. 1467--1489. PAPIKE J. J. and BE~CE A. E. (1978) Lunar mare versus terrestrial mid-ocean ridge basalts: planetary constraints on basaltic volcanism. Geophys. Res. Lrtt. 5, 803-806. PAPIKE J. J.. HODGES F. N., BENCE A. E.. CAMERON M. and RHODES J. M. (1976) Mare basalts: Crystal chemistry, mineralogy. and petrology. Rev. Geuph~s. Spuce Phgs. 14.4755540. RAMMENSEEW. (1977) Distribution of trace elements in metal-silicate systems and implications for some cosmochemical problems. Thesis (in German), Universitat Mainz. R~ucwtxm A. E. (1966) Chemical evolution of the terrestrial planets. Grochim. Cosmochtm. Acta 30, 41-104. RINGWOOD A. E. and KESSOK S. E. (1977) Basaltic magmatism and the bulk composition of the Moon. II. Siderophile and volatile elements in Moon, Earth. and chondrites: implications for lunar origin, Tlir !&foct/~ 16, 425364. RINGW~~D A. E.. DELANO J. W., KESSON S. E. and HI~RERSC)~ W. (1980) More on lunar siderophiles: The strange case of rhenium. Luttur Pfurref. SCZ. XI, pp. 929-93 1, SATO M.. HICKLING N. L. and MCLAN~ J. E. (1973) Oxygen fugacity values of Apollo 12, 14. and 15 lunar samples and reduced state of lunar magmas. Proc. 4th Lunur SC;. corlf: pp. 1061 1079. SHAW D. M. (1968) A review of K-Rb fractionatioI1 trends by covariance analysis, Grocftim. C~~.~~nu~~~i~n. Actu 32. 573-601. SHAW D. M. (1972) Development of the early continental crust. Part 1. Use of trace element distribution coefficient models for the protoarchean crust. fun. J. Fur& Sci. 9, 3577-1595. SHAW D. M. (1979) Development of the early continental crust. Part 3. Depletion of incompatible elements in the mantle. Precamb~iun Rrs.. in press. SMALESA. A.. HVC;HEST. C.: MAPPER D., MCI~NES C. A. J. and WL;BSTERR. K. (1964) The determination of rubidium and caesium in stony meteorites by neutron activation analysis and by mass spectrometry. Grochirn. Co.+ mochirn. Actu 28. 209-133. SMITH J. D. and BL’RTON J. D. (1972)The occurrence and distribution of tin with particular reference to marine environments. Geochim. Cosmochim Actu 36, 62 l--629. SMITH J. V. (1977) Possible controls on the bulk composition of the Earth: imohcations for the oriein of the Earth and Moon. Prdc. 8th L~nur Sci. ?onf:. pp. 333 369. SMITH J. V., AUI)ERSON A. T.. NEWTON R. C.. 0Lst.x E. J. and WYLLIE P. J. (1970) A petrologic model for the Moon based on petrogenesis. experimental petrology, and physical properties. J. Geol. 78. 381-405. TAKAHASHI H.. JAUSSENS, M.-J., MORGAN J. W. and ANDERS E. (1978) Further studies of trace elements in C3 chondrites. Geochlm. Cosmochim. Acta 42, 927-930. TAYLOR S. K. (197Ya) Nickel abundances in lunar mare basalts. Llmur Plunet. Sci. Ii’, pp. 12 15 1216. TAYLOK S. R. (1979h) Relative refractory and volatile ele-

2124

R.

WOLF

and E.

ment contents of the Earth and Moon. Lunar Planet. Sci. X, 1217~1218. TUREKIANK. K. and CLARKS. P. Jr (1969) Inhomogeneous accumulation of the Earth from the primitive solar nebula. Earth Planet. Sci. Lett. 6, 346-348. WAI C. M. and WASSONJ. T. (1977) Nebular condensation of moderately volatile elements and their abundances in ordinary chondrites. Earth Planet. Sci. Lett. 36, I-13. WAI C. M. and WASSON J. T. (1979) Nebular condensation of Ga, Ge, and Sb and the chemical classification of iron meteorites. Nature 282. 79c793. WAI C. M., WETHERILL G. W. and WASSONJ. T. (1968) The distribution of trace quantities of germanium between metal. silicate and sulfide phases. Geochim. Cosmochim. Acta 32, 1269-I 278.

WALKERD., LONGHIJ. and HAYSJ. F. (1975) Differentiation of a very thick magma body and implications for the source regions of mare basalts. Proc. 6th Lunar Sci. conf: pp. 110331120. WALTERL. S (1969) The major-element composition of individual chondrules of the Bjurbijle meteorite. In Meteorite Research (ed. P. Millman), pp. 191-205. Reidel. WE~NKEH.. BADDENHALJSEN H., DREIBUSG., JAG~UTZ E., KRUSEH., PALMEH., SPETTELB. and TESCHKEF. (1973) Multielement analyses of Apollo 15. 16, and 17 samples and the bulk composition of the Moon. Proc. 4th Lunar Sci. Conf: pp. 1461-1481. WASSERRURG G. J., MACDONALDG. J. F., HOYLEF. and FOWLERW. A. (1964) Relative contributions of uranium, thorium, and potassium to heat production in the Earth. Science 143, 465467.

ANDEKS

WASSERBURG G. J. and DEPAOLOD. J. (1979) Models of Earth structure inferred from neodymium and strontium isotopic abundances. Proc. Natl. Acad. Sci. U.S.A. 76, 3594-3598. WASSIN

J. T. (1971) Volatile elements on the Earth and the Moon. Earth Planet. Sci. Lett. 11, 219-225. WHITEW. M. and BRYAN W. B. (1977) Sr-isotope, K, Rb, Cs, Sr, Ba, and rare-earth geochemistry of basalts from the FAMOUS area. Geol. Sot. Am. Bull. 88, 571-576. WHITEW. M. and SCHILLINGJ.-G. (1978) The nature and origin of geochemical variation in Mid-Atlantic Ridge basalts from the Central North Atlantic. Geochim. Cosmochim. Actu 42, 1501-1516.

WIESMANN H. and HUBBARDN. J. (1975) A compilation of the lunar sample data generated by the Gast, Nyquist, and Hubbard lunar sample PI-ships. Unnumbered Report, NASA-JSC, March 1975, 50 pp. WOLFR., W~C~DROW A. and ANDERSE. (1979a) Siderophile and volatile elements in the Earth and Moon: Similar or not? (abstract). Lunar Planet. Sci. X, pp. 1361-1363, The Lunar Science Institute, Houston, WOLF R., W~C~DROW A. and ANDERSE. (1979b) Lunar basalts and pristine highland rocks: Comparison of siderophile and volatile elements. Proc. 10th Lunar Planet. Sci. Conf: pp. 210772130. WOLF R., W~QDROWA. B., RICHTERG. and ANDERSE. (1980) Chemical fractionations in meteorites. XI. C2 chondrites. Grochim. Cosmochim. Acta 44, 7 I 1-717. Wool J. A. (1962) Chondrules and the origin of the terrestrial planets. Nature 194, 127-130. Wool J. A. (1963) On the origin of chondrules and chondrites. Icarus 2, 152-180.