Partitioning of rare earth, alkali and alkaline earth elements between phenocrysts and acidic igneous magma

Partitioning of rare earth, alkali and alkaline earth elements between phenocrysts and acidic igneous magma

Geochimics et Cosmochimica Acta,1971,Vol.36,pp.963to 968. Pergamon Press.Printed in Northern Ireland Partitioning of rare earth, alkali and alkaline ...

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Geochimics et Cosmochimica Acta,1971,Vol.36,pp.963to 968. Pergamon Press.Printed in Northern Ireland

Partitioning of rare earth, alkali and alkaline earth elements between phenocrysts and acidic igneous magma HIROSHI NA~ASAWA and CHARLES C. SCHNETZLER Planetology Branch, Goddard Space Flight Center, Greenbelt, Maryland 20771 (Received 21 December 1970; accepted in revised form 2.5May 1971) Abstract-Concentrations of rare earth, alkali and alkaline earth elements in phenocryst and groundmass components of pyroclastic dacites have been measured. Mafic mineral rare-earth partition coefficients are much larger in these dacites than in more basic rocks. This may be due to differences in host ion concentrations in basic and acidic magmas. Because of these high partition coefficients, especially for hornblende, crystallization of appreciable hornblende, zircon and apatite could reduce the concentrations of rare earth elements in acidic magmas during crystallization differentiation. INTRODUCTION FOR A differentiating silicate magma, the partition coefficients of rare earth elements (REE) between the liquid phase and crystallizing mineral phases are the most important factors controlling changes in the REE abundances in the magma. The term “Partition coefficient” is defined in this paper as the ratio of concentration of a particular element in the solid (mineral) to the concentration of the same element in the coexisting liquid (groundmass). A number of REE patterns for various igneous rock-types from ultrabasic through acidic, and also a number of partition coefficients of REE between common rock-forming minerals and groundmass matrix materials have been published (SCHNETZLERand PHILPOTTS, 1968, 1970; ONUMA et aZ., 1968; HI~UCHI and NAGASAWA, 1969). REE abundance patterns are also available for some particular sequences of rocks, for example, volcanic rock sequences from Hawaii (SCHILLING and WINCHESTER, 1968), Izu-Hakone, Japan (YAJIMA et al., 1968), Gough Islands (ZIELINSKI and FREY, 1970), the layered series of gabbro from the Skaergaard intrusion (HASKIN and HASKIN, 1968) etc. In basic and ultrabasic sequences the crystallizing rocks have concentrations of REE which are usually much smaller than those in the liquid magmas, resulting in a considerable enrichment of REE in the residual liquid phase during differentiation. This is consistent with previously published partition coefficients, which are usually less than one for the common rock-forming minerals (except garnet). However, in some sequences, especially among acidic members, observed variations in absolute abundances of REE are very small or even show decreasing REE concentrations with increasing differentiation (YAJIMA et al., 1968). In order to explain these difficulties, two alternatives have been considered : (1) Partition coefficients of REE for common rock-forming minerals increase as differentiation proceeds. (2) The effect of minor or accessory minerals are not negligible. To check these possibilities, REE abundances in acidic volcanic rocks from southern Kyushu, Japan have been determined. The alkali (Li, Na, K, Rb) and alkaline earth (Ca, Sr, Ba) elements have also been determined for two of the dacite samples. A whole rock sample of basalt (JB-1, a 953

954

HIROSHI NAQASAWA and CHA.RLESC. SCHNETZLER

standard rock sample of Geol. Survey of Japan) collected from Kyushu, Japan, has been analyzed for comparison. EXPER~E~TAL

~OCE~~RES

AND SABLES

The analytical method for the REE, Li, K, Rb, Sr md Ba was mass spectrometric isotope dilution, and was essentiallythe same as describedby SCHNETZLER et al. (1967), MASUDA (1968) and PHILPOTTSrendSCHNETZLER(1970). Na and Ca are determined by the atomic absorption method. The precision of duplicate REE analyses are usually better than *5 per cent, but some data may be of poorer quality due to factors such as low concentration, small sample size and/or interference in mass spectrometry (which are indicated in Table 2). Because hypersthene contains very low concentrationsof K, Rb and Ba, the values of these elements in hypersthenes are subject to high blank correction. For example, K, Rb and Ba values for Kakuto hypersthene required about 30, 10 and 25 per cent blank correction, respectively. However, these values are still meaningful as far as the discussionis concernedwith orders of magnitude differencesin partition coefficients. The samples analyzed in this study are seven pyroclastic daeite pumices collected from southern Kyushu and one from Hijiori, northern Honshu, Japan and one tit~au~~ basalt (JB-1) from Kyushu, Japan. The dacite samples are composed of dominant porous glassy groundmass with a small amount of phenocrystic hornblende, augite, hypersthene, plagioclase, quartz etc., ranging from a few to about 30 per cent (Appendix 2). Because the groundmassesof the dacites are porous and permeable to water, it is possible that some components in the groundmasseshsve been lost by leaching with ram water. However, the similarity of pa~ition pattern for the same mineral in differentd&cites,in spite of their different ages, history and condition of deposition, etc., suggests leaching was not significantfor the REE. Leaching of alkali and alkaline earth elements may be larger than for REE. From similar partition coefficientsof alkali and alkaline earth elements for the Torihama and Kakuto &cites, however, the effect seems minor for these elements also. The mineral phases were separated by using organic liquids and electromagnetictechniques after most of the porous, glassy ~o~drn~s materials had been washed off with rumung water. The purity of the separates was judged to be above 99 per cent by microscopic inspection. The maximum groundmass impurities in the Kakuto hypersthene was less than 0.05 per cent, as judged from the low contents of Da and Rb. The groundmass sample of the Kakuto dacite was separated from the sintered upper part of the deposit, whereas the phenocryst samples were separated from lower part of the approximately 30 m thick deposit because of the difficulty in separating all phases from the same material. This, in part, msy be responsiblefor the low REE partition eoeffi~ientsfor the Kakuto samples. However, from the similarity of most alkali earth partition c~fficients and of relative REE partition patterns for Kakuto and Torihama dacites, it is plausiblethat this is not a serious cause of the differencein absolute REE partition coefficients. Other groundmassand phenocryst samples were separated from the same specimens. RESULTS AND Dxsouss~o~

The calculated partition coefficients of REE between phenocryst minerals and groundmass are listed in Table 2 and are plotted in Fig. 2. These data are notable in that most of the partition coefficients of REE for mafic minerals are well above the ranges of those already reported for the same minerals in more basic rocks, such as basalts and andesites (SC~ETZLE~ and PHILPOTTS, 1968, 1970; OKUMA et cd., 1968; HIGGCHI and NAGASAWA, 1969), although the relative REE patterns for the same minerals are similar. The partition patterns for three hornblendes are quite close one to another, while the Kakuto hornblende pattern is lower than the other

Partitioning Table

1. REE

contents

in the groundmass samples of dacites and the whole-rock basalt in ppm

sample of

7 Ata (II)’ Kyushu

Ikeda Kyushu

Beealt 11 Matsure Kyushu (JB-1)

54 27.6 6.5 1.50 6.9 4.09 4.27 0.74

53 26.7 6.2 1.38 -

44.9 19.4 3.83 0.87 -

66.4 20.8 4.93 1.48 -

6.9 4.37 4.27 0.73

3.96 2.3* 2.94 -

68 47.6 35.1 21.1 22.8 22.5 22.7 21.8

67 45.2 33.5 19-4 22.5 24.0 22.7 21.5

Dacite

ROCk No.

1

2

Locality

Torihama Kyushu

Kakuto Kyushu

Concentration PPm

955

of rare earth, alkali and alkaline earth elements

Ce Nd Sm Eu Gd DY El. Yb LU

Ce Nd Sm Concentration ratio Eu rock/ohondrite Gd DY Er Yb LU

-

3 Hijiori Yama-gata Pref.

4 Ito (Ib) Kyushu

5 Ito (Tsumaya) Kyushu

42.3 15.0 2.64 0.414 2.43 1.77 2.00 0.39

63 26.7 5.7 0.93 5.4 5.4 3.16 3.20 0.54

29.7 12.8 2.63 0.68 2.31 1.55 1.91 0.395

45.5 17.3 3.31 0.68 3.37 3.34 2.09 2.19 0.37

48.2 18.0 3.59 0.60 -

54 25.9 14.3 5.8 8.0 9.7 10.6 11.5

79 47.1 30.7 13.1 20.9 17.4 17.4 17.0 16.0

37.7 22.1 14.2 9.6 7.6 8.5 10.2 11.6

58 29.8 17.9 9.6 13.2 11.0 11.5 11.6 10.9

61 31.0 19.2 8.4 12.4 -

2.34 -

6 Ata (I)* Kyushu

8

57 33.6 20.7 12.2 13.1 12* 15.6 -

4.06 2.19 2.01 0.318 84 35.7 26.6 20.8 13.4 12.0 11.0 9.4

* Ata I and II are not duplicate analyses of the mme sample, but were collected at different sites; nomenclature is from UI (1970)

three by factors of about 4-5. The pattern for Kakuto hornblende is very close to that for Ata augite. In the hypersthene patterns, larger scatter is seen for lighter REE than for heavier REE. The alkali element determinations in these samples show groundmass contamination is very small; thus this could not be the cause of the scatter. The plagioclase patterns also show some scatter, as shown in Fig. 2c, but they are quite similar in a relative sense and almost completely fall within the range of the basalt and andesite data. The large differences between the absolute values of partition coefficients for mafic minerals in dacites and those in basalts and andesites may be explained by the difference in Mg, Fe and/or Ca concentrations in the groundmasses. Because concentrations of Mg, Fe and Ca the main constituent cations in mafic minerals are much lower in acidic magmas than in basic ones, while the minerals are chemically stoichiometric; the partition coefficients of these “major” elements for mafic minerals are larger in acidic magma than in basic magma. Thus it follows that the partition coefficients of trace elements substituting for these host cations are expected to be larger in acidic rocks than in basic rocks, provided that other effects are smaller (this can be easily understood by considering the partition coefficients of minor isotopes of say Mg, which, of course, are essentially identical to those of the major isotope of Mg). Differences in ease of charge balance is another possibility. Because most REE would be in the + 3 valence state, substitution of REE for + 2 valent host ions should need charge balancing. The charge balance may be maintained by substitution of another pair, for example, Al-Si for Ca-Al in plagioclase. Other possible causes are differences in temperature, pressure and the crystal

HIROSHI NAUASAWA and CHARLES C. SCHNETZLER

956

Table 2. REE contents in phenocryst samples and the Mineral No.

1P

ppm

Plagioclase 4P 12.7 3.60 0.48 1.69 0.435 0.255 0.136 0.123 0.0201

DY Er Yb Lu

0.144 0.079 0.085 0.0152

6.8 1.69 0.28 0.77 0.092 0.069 0.012 t

CC3

0.270 0.191 0.125 2.35 0.059 0.0446 0.0425 0.0389

0.109 0.061 0.050 0.82 0.029 0.022 0.022t

11.4 2.87 0.327 0.97 -

C0

Concentration

2P

Nd Sm Eu Gd

Nd Sm Partition Eu coefficient Gd “Y Er Yb LU

0.279 0.290

0.144 2.49 0.129 0.076 0.065 0.056 0.054

6P

3.33 0.55 1.44 0.313 0.16* 0.129 0.022t

8P

1H

2H

15.6 4.65 0.59 2.45 0.308 0.194 0.0246

7.2 3.92 0.90 0.085 1.23 1.29 1.55 0.305

5.1 3.13 0.75 0.105 0.91 1.37 1.36 2.32 0.480

0.169

0.082 0.113 0.133 0.113 0.170 0.260 0.431 0.73 0.88

0.347 0.237 0.153 2.81 0.078 0.066 -

0.121 0.084 0.96 0.452 0.38* 0.302 0.29t

0.261 0.342 0.205 0.51 0.73 0.78 0.78

* Poor precision due to overlapping of contaminant peak in mass spectrometry. t Poor precision due to large correction from adjacent REE.

I

I

Ce

Nd

I

I

I

Sm Eu Cid

DY

Er

Yb

Lu

Fig. 1. Chondrite-normalized pattern of REE in the ground-mass samples of dacites; Torihama(O), Kakuto(O), Hijiori (a), Ito (@I),Ata (0) and Ikeda (a).

Partitioning

of rare earth, alkali and alkaline earth elements

957

calculated partition coefficient between phenocryst and groundmass Hypersthene 3H 4H

6H

1Hb

7.7 4.46 1.01 0.185 1.18 1.28 1.08 1.88 0.361

4.37 2.55 0.70 0.064 0.93 1.44 1.34 2.03 0.421

4.37 3.29 1.05 0.191 -

60 64 21.5 2.45 -

2.38 2.16 3.11 0.57

32.9 19.1 17.3 2.3

0.262 0.348 0.384 0.270 -

0.096 0.147 0.210 0.093 0.276 0.431 0.64 0.93 1.14

0.082 0.119 0.162 0.127 -

0.55 0.70 0.99 0.92

0.334 0.53 0.73 0.76

1.42 4.25 8.2 5.9 13.5 10.8 8.7 5.9

Hornblende 2Hb 3Hb 26.7 28.5 9.3 1.29 11* 12.2 7.5 6.1 0.95 0.429 1.03 1.61 1.39 2.0* 2.31 2.38 1.89 1.75

8Hb

Augite 6Au

40.9 52 18.5 3.41 8.8 17.4 17.1 2.5

80 87 30.5 3.94 -

19.2 25.9 9.9 1.67 -

51* 33* 21.9 1.97

18.2 9.2 8.6 1.34

1.38 4.03 7.1 5.0 12.5 11.2 9.0 6.3

1.77 4.49 8.0 4.53 13* 14* 7.45 -

0.362 0.94 1.52 1.11 2.63 2.25 2.01 1.81

Apatite 2A 1040 580 117 13.5 117 89 44 30.0 4.32 16.6 21.0 20.7 14.5 21.7 16.9 14.1 9.4 7.9

Mineral No.

Concentration ppm

Ce Nd Sm Eu Gd DY Er Yb Lu

Ce Nd Sm Partition Eu coGd efficient Dy Er Yb Lu

structure of minerals. Little is known about these effects on REE partition coefficients as yet, but they are seemingly not large. Judging from the similarity in the relative REE partition patterns, the effect of changes in the size of the lattice sites may be small. In either of the first two possibilities, the partition coefficients would be very sensitive to the chemical composition of the groundmass. Because both REE and host ion partition coefficients for plagioclase show much smaller difference between acidic and basic magma than those for mafic minerals, the change in the host ion concentration seems to be the most reasonable explanation for the difference in REE partition coefficients. However, because no linear relationships between REE and host ion partition coefficients have been observed, two or more effects may be operative to cause variations in partition coefficients. The REE partition coefficients for Kakuto hornblende in Fig. 2b are considerably smaller than those for the other three hornblendes. The major element compositions of groundmasses and hornblendes are quite similar for these samples, as far as the available analytical data are concerned. The REE partition coefficients for hypersthene and plagioclase are also smaller for Kakuto dacite than for the other three dacites, but the differences are not as large as in the case of hornblende. Likewise, the partition coefficients of Sr, K, and Rb for phenocrysts from the Kakuto dacite are almost always smaller than those for the Torihama dacite (Fig. 3). The reason for these differences are unknown. The partition coefficients of alkali and alkaline earth elements in two dacites are listed in Table 3 and are plotted in Fig. 3 against ionic radius, together with previously published data obtained from more basic rocks. These patterns are similar to those

HIROSHINAGASAWAand CHARTZSC. SCHNETZLER

a) Hypetsthene

b) Hornblende

Ce

Nd

Sm Eu Gd

Dy

Er

Yb Lu

Fig. 2. Pmtition coefficients of REE between hyperstbene, hornblende and plagioclase and groundmass; (8) hypersthene, (b) hornblende, (c) plagioolaso. Loo&ion code same as Fig. 1. The shaded me& shows the range of pm%ition coefficientsfor basalts and andesites.

Partitioning

of rare earth, alkali and alkaline earth elements

959

of ONUIUA et al. (1968) and HIGUCHIand NACIASAWA (1969) at least in their essential features. Partition coefficient values for the two dacites show fairly good agreement except for Sr values, and K and Rb values for hypersthene. The partition coefficients of K, Rb, Sr and Ba for hornblende in dacites, in contrast to those of REE, are much smaller than those for hornblende in basalt and andesite reported by PHILPOTTS and SCHNETZLER (1970). This suggests that these elements, having larger ionic radii, do not occupy the Mg-site or Ca-site in hornblende. They would occupy the larger,

(a) Hypetsthene

1

(b) Hornblende

(c) Plagioclase

U.b

0.8

1.o

1.2

ionic Radius

Fig. 3. Partition coefficients of alkali and alkali earth elements for Torihama and Kakuto dacites vs. ionic radius. (a) hypersthene, (b) hornblende, (c) plagioclase. Torihama (open symbols), Kakuto (closed symbols). Ionic radii of SRANNON and PREWITT (1969) are used. The values by ONUMA et al. (x) and the range of the values by SCHNETZLER and PHILPOTTS (bar) are also shown.

960

HIROSHI

NAQASAWA

and CHARIJGS C.

SCHNETZLER

Table 3. Contents of alkali and ralkali-earthelements in groundmass and phenocryst samples in two dacites

Locality mineral Li Na. (%) K(%) Rb Concentration* Mg ppm ::( %, Sr Ba

Partition coefficient

l

Ground-8 (1)

Torihama, Hornblonde (1Hb)

Kyushu Hypersthene

22.6 2.49 2.58 107 0.26 500 1.10 93.6 478

5.02 0.96 0.208 1.47 6.30 5,300 7.26 21.0 20.9

4.77 0.00601 0.291 12.62 14,600 0.60 0.80 1.41

0.22 0.386 0.081 0.014 24.2 11 6.3 0.0224 0.044

0.21 0.0023 0.0027 48.5 29.2 0.56 0*0085 0.0029

Li N& K Rb Mg Mn Ce Sr Ba

(1H)

PI&oclsse (1P) 14.9 4.14 O-266 4.44 4.61 416 147 0.66 1.66 0.10 0.041 4.25 4.4 0.308

(2)

Kakuto, Hornblonde (2Hb)

Kyushu Hyporsthene (2H)

40.6 2.97 3.39 145 0.26 403 2.97 384 609

7.2 1.10 0.222 1.11 4,800 7.93 36.0 33.1

6.40 0.00185 0.069 13.15 13,600 1.42 17.5 1.5

0.18 0.41 0.065 0.0077 11.9 5.8 0.094 0.054

0.16 0*00056 0~00048 60.6 33.7 1.04 0.046 0.0025

Groundm888

Plagio 0lLl.S~

(2P) 10.9 4.73 0.259 2.32 5.21 556 185 0.27 1.59 0.076 0.016 3.85 1.46 0.304

PPM is used unless noted.

otherwise vacant site in hornblende structure, so that their behaviors are quite different from those of REE. It is also seen in Fig. 3 that Li partition coefficients for hornblendes and hypersthenes are considerably smaller than those of Mg and Mn, which have similar ionic radii to Li. This suggests that the Mg-site in hornblende and hypersthene does not readily accept + 1 valent ions probably because of difficulty in charge balance. The smaller partition coefficient values of K, Rb, Sr and Ba for hypersthene are difficult to explain by a method similar to that discussed above. However, because the concentration of these elements in hypersthene (as well as their partition coefficients) are very small, these differing values may be due to differing amounts of some impurity in the hypersthene separates analyzed. All partition coefficient patterns except for plagioclase, show negative Eu anomalies. This, along with the large positive Eu anomalies in plagioclase, suggests that a considerable part of the Eu was in the divalent state in the dacite magmas. Contamination of groundmass separates by small amounts of phenocrystic plagioclase is another explanation of the negative Eu anomalies. However, this possibility is not likely because the negative Eu anomalies are observed even in cases where Eu concentrations in plagioclase are almost the same as those in the groundmass. According to PHILPOTTS (1970), we can calculate Eu2+/Eu3+ ratios in coexisting phases, by postulating that the Eu2+ partition coefficient is identical to that of Sr. The Eus+/Eua+ ratios in the groundmass of Torihama and Kakuto dacites, calculated for groundmass-feldspar pair, are 1.05 and 1.27, respectively; those in plagioclase 46.6 and 40.8, respectively. These values suggest highly reducing conditions in the dacite magmas, which coincide with the low oxygen fugacity in Ikeda and Hijiori dacites (3 x lo-16 atm at 740°C and 5 x lo-l4 atm at 780X, respectively) estimated

Partitioning of rare earth, alkali and alkaline earth elements

961

by compositional relationships between coexisting magnetite and ilmenite (UI, 1970). The ratios of Eu2+/Eu3+ in feldspars to those in groundmasses fit nicely on the plot of this ratio versus plagioclase anorthite content shown in PHILPOTTS (1970). Effect of mineral crystallization on the REE pattern in the liquid Hypersthenes show simple partition patterns increasing towards heavier REE as shown in Fig. 2a. The crystallization of hypersthene from acidic magmas would result in simple enrichment of the light REE. On the other hand, the partition patterns of augite and hornblende have maxima around Dy, so that the crystallization of these minerals give rise to upward concave pattern in the liquid phase. This trend may be seen in Fig. 1; i.e. the chondrite-normalized values of Dy and Er are smaller than those of Yb for Torihama, Hijiori and Ikeda dacite which show considerable hornblende crystallization. Crystallization of plagioclase from a magma should result in relative enrichment of heavier REE over lighter REE. This effect would usually be very small, however, because all partition coefficient values in plagioclase, except that of Eu, are much lower than unity; the resulting enrichment of REE in the liquid would be large but not very selective, unless there is quite extensive crystallization of plagioclase. The partition coefficients of heavy REE for zircons are very high (about 300400 for Lu) and those of lighter REE decreases rapidly to less than 10 for Ce (NAGIASAWA,1970). Apatites also show very high REE partition coefficients with maxima at about Gd (Table 2). Because of these high partition coefficients and characteristic patterns, their crystallization from magmas could change considerably the REE pattern in the liquid, if the amounts crystallizing from the magma are significantly large. The effect of crystallization of minerals on REE concentrations in a magma can be quantitatively determined if the amounts crystallized and the partition coefficients are known for these minerals. We have applied the partition coefficient data to the modal abundances shown in Appendix 2 to see if these values explain differences in the groundmass REE patterns. The concentrations of REE in the solid phase (C,) removed from liquid magma at a stage of differentiation may be estimated by multiplying the concentration in the liquid (C,) by the apparent partition coefficients (D) between the liquid magma and the crystallizing bulk solid. The apparent partition coefficient is defined by the ratio of the average concentrations in the bulk solid to those in the liquid phase or D = C,/C, = 2 wi . di i where d, denote the partition coefficient between ith mineral and liquid and wi denote the fraction for ith mineral. We used modal abundances for wi’s to estimate the apparent partition coefficients. Because the settling rates of phenocryst minerals are different one from another, Fig. 4 gives only rough estimates of the effect of mineral crystallization in the dacite magmas. It is interesting that the estimated apparent partition coefficient pattern for the Ata dacite (Fig. 4a) is almost flat excepting Eu. The effect of augite, plagioclase, hypersthene and apatite are almost in the same order of magnitude, and one effect

962

EIBOSRI NAGASAWAand CHARLESC. SCHNETZLER 1

I

I

I

I

I

I

f

I

I

0.1

0.01

I

?i

w

0.1

2 Y

s

0.01

F5 F

s

Lz

0.001 t

-I

I

0.:

0.0’

0.00

J

I

k

Nd

f

I

I

SmEu Gd

I

I

Dy

Er

,

L

Yb I..U

Pig. 4. The calculated apparent partition coefficientsbetween crystallizing solid and residual liquid phase in da&es (solid line). Contribution of each mineral is also shown. (a) Ata; Partition coefficientsfor Ito Goon were used for calculation. (b) Ito; Partition coefficients for Ata augite were used for cumulation. (c) Torihama.

cancels another to produce a flat pattern. Hence, in the course of crystallization differentiation of the Ata dacite magma, considerable absolute, but little relative, ~actionatio~ of REE seems to have occurred. In the Ito dacite (Pig. 4b), the amounts of mafic minerals, plus zircon and apatite are so small that the pattern of the calculated apparent bulk partition coefficient is similar to the partition pattern for plagioclase. The crystallization differentiation of the Ito dacite magma would result in a considerable enrichment of REE, a slight enrichment of the light REE over the heavy REE, and a large negative Eu anomaly in the liquids; this is essentially the pattern observed. In the eases of Torihama (Fig. 40) and Hijiori dacites, in which hornblende phenocrysts are abundant, the effect of hornbIende crystahization seems most responsible for the production of the REE pattern in the liquid (Fig. 1). The apparent

bulk partition pattern for Hijiori dacite seems to be similar to that for Torihama dacite, although the bulk partition pattern was not calculated because the abundances of zircon and spat&e, and the BEE pa~ition ~~~~ients for pl~gio~l~e are not known for this da&e. The absolute values, however, may be ~me~h~t higher for Hijiori because of higher hornblende abundance in this daeite. The low concentration and the upward concave pattern of REE in the Torihama and Hijiori dacites seem to result from the apparent partition coefficient pattern shown in Fig. 442. The Ikeda da&e may show a similar apparent bulk partition pattern of REE to those for T~rihama and Hijiori, but the contribution ofzircon,apatite and pl~gio~l~e could be larger than those in Torihama and Hijiori because of smaller abundance of hornblende The contributions of zircon and apat’ite shown in Fig, 4 do not exceed those of more common minerals. However, the effects of these minerals could be somewhat under~stimated~ inasmuch as estimated yields in mineral separation were used in the ~a.l~u~~tions instead of modal ~bn~d~~~s~ and there may have been ~onside~ble loss of these minerals during separation. In Fig. 4, no apparent bulk partition coefficient larger than one, except for En, is shown, although those of intermediate REE in the Torihama dacite are close to one. However, beoause of high hornblende abundance in Hijiori dacite, the apparent bulk partition c~~~ients for Hijiori da&e are expected to be larger than one for Sm through Yb, even if the ~ontrib~~~ion of undetermined minerals is negli~bl~~ small. In spite of the large partition coefficient values for hornblende and augite, over-all orystallization effects of miner& rarely reduce the REE concentration in the magma, because the amounts of mafic minerals crystallizing from acidic magma are limited by the low ~~~~ntration of LMg,Fe and Ca in the liquid. Even if the ~on~ntr~tio~s of these ions in the magma were large, the increase in the host ion ~on~en~~tio~ would reduce the partition coefficient values as discussed in the preceding section to cancel the effect. From these considerations, the condition in which the concentration of most REE decreases in the liquid with differentiation can probably be met only when the fraction of crystallizing hornblende, zircon and/or apatite a-reextmmely high. 2%~ o~~~~ of the ~~~~~~~~~~ The origin of dacitio magmas has been discussed petrologically by a number of workers (e.g. STEINER, 1963; EWARTand STIPP, 1968). Partial melting of granite, basalt, andesite or sedimentary rocks and crystallization diffefentiation of basalts have been proposed, Usa ( 1960) suggested that &beOsumi granitiicinvasion exposed in southern Kyushu is the original material from which the Ata and Ikeda da&es have been derived by partial or near-complete fusion. Ur (19?0), on the other hand, suggested partial melting of sedimentary rock for their origin, based on their similarity to the magma of pyroclastic flow in the Taupo volcanic zone, New Zealand (EWART, 1965; EWAXTand STTPP,1968; EWARTet oI., X%23). According to Uz the daeite from %hesoutber~ Kyushu area are ~hara~te~z~d by: f%)their large volumes &he amount of each flow is up to more than f6O kma), (2) the volume of da&e and andesite in this area are almost equal, and a composition gap {about 14 per cent in diflerentiation index, or 6 per cent in SiO, content) is seen between the andesites and dacites.

HIROSHINACASAWAand CHARLESC. SCENETZLER

964

I

I

I

Ce

Nd

I

I

I

Sm Eu Gd

I

I

Dy

Er

I

/

i

Yb Lu

Fig. 6. Chondrite-normalizedpattern of REE in the Osumi (0) and the Takakuma granite ( l), Matsura basalt (A) and European shale (0) oompared with those for the da&es (shown by the shaded area).

The chondrite-normalized REE patterns of the d&cite groundmasses shown in Fig. 1 are very similar, suggesting a similar origin. If the Ata dacite magma has been produced by the partial melting of ths Osumi granite, the residual solid left after the partial melting of the granite should be enriched in light REE and depleted in heavy REE and Eu compared with Osumi granite. The trend of the REE pa~ition pattern between the Ata dacite magma and the possibIe residual solid is somewhat similar to the partition pattern between plagioclase-rich solid and liquid as shown in Fig, 4b, but has no positive Eu anomaly and tho absolute values of partition coefficient for light REE are too high for plagioclase. Because no partition patterns which decrease towards the heavy REE are known for common rock-forming minerals except feldspar, the partial melting of the Osumi granite is an unlikely origin of the Ata dacite magma. For the Ikeda dacite, the Osumi granite seems a little more However, the severe problem likely to be the original material, at least qualitatively. of absolute partition coefficient values argues against this possibility. The Takakuma granite shows very low concentration of heavy REE (Fig. 5), so that the production

of dacite magma by partial fusion requires the enrichment of

Yb and Lu by at least a factor of 3. This probably restllts in a considerable enrichment of the light REE at the same time. Because the concentration of the Ce in the dacites is almost equal to that of Takakuma granite, the origin of the dacite magmas can hardly be explained by the partial melting of the Takakuma granite. Using similar reasoning and because of the quite different chemical compositions, the partial melting of an alkali basalt having a similar REE pattern to JB- 1, the Matsura basalt, is also an unlikely origin of the dacites-the light REE contents in the basalt are too high to produce dacite magma by partial melting. Only rocks with low light REE concentrations, such as tholeiitic basalts or andesites, meet requirements for the dacite parent material from the view point of the REE patterns.

Partitioning of ram earth, alkali and alkalin6 e&h elements

965

However, the chemical composition of these rocks are so different from those of d&cites, that the feasibility of the application of our measured partition coefficients is quite doubtful. The ~dirn~n~y rocks are another possible source material of the da&e magmas. The relative REE pattern for the average European shale determined by HASKIN and &SKIN (1966) resembles closely the dacite pattern although the REE abundances in the European shale are a little greater than those in the d&cites. Because of the close resemblance iu REE pattern, it5well as in chemical composition, complete or near complete fusion of shales could produce da&e magma, However, X.71~1~~~~ pointed out that CaO contents in basement ~diment~ry rocks in the southern Kyushu (Nichinan formation and Paleozoic shale) are too low to produce dacite magma. Thus it appears that no suggested single model is readily applicable for the origin of the d&cite magmas. cONGIXX+K@ET

The conclusions obtained in this study are summsrized as follows: 1. Partition coefficients of REE for mafic minerals are considerably larger in decite than in more basic rocks. This may be explained in part by the differences in host ion concentrations in basic and acidic magmas. However, more than one effect appears to be responsible for the measured variation of the partition coefficients. 2. Zircon and apatite show very high partition coefficient values and characteristic patterns for the REE. However, the amounts of zircon and apatite in the d&cites studied here are so small that their effects seem not to appreciably exceed those of common rock-forming minerals. 3. The effect of crystallization of hornbIende, or of much zircon or apatite, could give rise to higher REE concentrations in the ~~s~~~i~ng sofid than in residual acidic magma. This may be responsible for the trend in REE variation observed in some acidic magma, in which REE concentrations stay almost constant or decrease during the latter part of crystallization differentiation. ~~~~w~~g~~~n~~-~~ sincerely thank Dr. J. A. PHILPOTTSand Mr. H. H. %OxAS for helpful discussions; Mr. T. FUKXJOKA, Dr. 5. AUXAKI,&. T.Uxand Z)F.I.K~~~~~~Ofort~~~rradviee snd use of samples; and to Mr. P. SEADIDfor aid in mass speetrometry, and to Dr. D. NAvA for aid in atomic absorption spectrometry.

REFEBENCES S. and UI T. (1966) Aim and Ata pyroclastic flows and related caldora depressionsin southern Kyushu, Jzq+n. B&l. Vulaxaol. 29, E&-48. EWART A. (1965)Minerrafogy and ~~~~~~~es~~ of the Wbakanam ignimbrite in the Maraetai area of the %upo volcanic zone, New Zealand. N.Z. J. G&E, &O&K+. 8, 611-677. EWABT A. and STIPPJ. J. (1968) Petrogenesisof the volcanic rocks of the central North Island, New Zealand, as indicatedby a study of Srs7/Srssratios, and Sr, Rb, K, U and Th abundances. Qeochim. Cosmochim. Acta 32, 699-736. Ew~ar A., TAYLOR S. R. and Cm A. C. (1968) !l’mce and minor element geochemistry of the rhyolitic volcsx~icrocks, centrsl North Island, New Zealand. Con~&b.X&.e~al. P&ml, 18, 76-164. H&XIX’ M. A.. and HASKIN L. A, (1966) Rare earths in European shales. SeieBm ~!!i4,507-509. HASKIN L. A. and HASKM M. A. (1968) Rare-earth elements in the Skaergwwd intrusion. Geochim. Cosmochim. acta 32, 433-447. ARAIUKI

966

HIROSHI NAGASAWA and CHARLES C. SCHNETZLER

HIGUCH~ H. and NAGASAWB, H. (1969) Partition of trrtce elements between rock-forming minerals and the host volcanic rocks. Earth PEaset. Sci. I&t. 7, 281-287. KURASAWA H. (1969) First compilation of analytical data and strontium isotopes on the new geochemical rock standards, JB-I, and SC-l. Mass S~~tro~c. 17,649-652. MASUDA A. (1968) Lanthanides in Norton County achondrite. Qeochem.J. a,11 l-1 35. NAQASAWA H. (1970) Rare earth concentration in zircon and apatite and their host d&cites end granites, Earth Planet. Sci. Lett. 9, 359-364. OBA N. (1960) The southern Osumi granite. &f&c. Rep. Res. Inst. Natural Resources No. 52-53, 127-135 (in Japanese). Om N., HIGUCHI H., WAKITA H. and NAUASAWA H. (1968) Trace element partition between two pyroxenes end the host volcanic rocks. Earth PZa%et. Std. Lett. 5, 47-51. PHILPOTTS J. A. and SCHNETZLXRC. C. (1970) Phenocryst-matrix partition coefficients for K, Rb, Sr and Ba with application to anorthosite end basalt genesis. Geochim. Cosmochim. Acta 34, 307-322. PHILPOTTS J. A. (1970) Redox estimation from a calculation of l&s+ and Eug-t concentrations in natural phases. Earth Planet. Sci. Lett. 9, 257-268. SCHILLING J. G. and WINCB~STER J. W. (1968) Rare-earth in Hawaiian basalts. SciePace153, 867-869. SCHNETZLERC. C., THOMAS H. H. snd PH~LPO~S J. A. (1967) Determination of rare earth elements in rocks and minerals by mess spectrometric, stable isotope dilution technique. And. Chem. 39, 18881890. SCHNETZT;ERC. C. and PHILPOTTS J. A. (1968) Partition coefficients of rare earth elements and barium between igneous matrix materials and rock forming mineral phenocrysts-I. Orz@a ano?D~t~b~t~o~ of the elements (editor L. H. Ahrens), pp. 929-938. Pergamon Press. SCHNETZLBR C. C. end PHI~P~TTS J. A. (1970) Partition coefficients of rare earth elements and barium between igneous matrix materials and rock forming mineral phenocrysts-II. Geochim. Cosmochim. Acta 34, 331-340. SHANNON R. D. and PREWITT C. T. (1969) Effective ionic radii in oxides and fluorides. Acta Crystallogr. B25, Part 6, 925-946. SHIBATA H. (1967) N&on Gaweki-shi, Vol. 2, p. 350, Asakura. Shoten. STEINER A. (1963) Crys~lli~ation behavior end origin of acidic ignimbrite and rhyolite magma in North Islend of New Zealand. Bull. PoEcanoE.25, 217-241. UI T. (1970) Genesis of magma and structure of magma chamber of several pyroelastic flows in Japan. J. Pac. Sci. Tokyo Univ. Sec. II, in press. UI T. (1967) Geology of Ibusuki area, southern Kyushu, Japan. J. Geol. Sot. Japan 73,477~490 (in Japanese). YAJI~ T., HIGUCHI H., BANNO S. and NAGA~AWA H. (1968) Differentiation of rocks in TzuHakone region; 8 study of rare earth patterns. Ch~ky~k~a~~ 2,24-25. ZIELINSKI R. and FREY F. (1970) Rare earth distributions in the alkeli basslttrachyte series of Gough Island. Trans. Amer. Geophys. Union 51, 451.

Partitioning of rare earth, alkali and alkaline earth elements

967

A~PPENDIX Appendix

Rock or mineral No. Locality

TiOt SiO AIs% Fe,% Fe0 MtlO MgO CaO NasO KsG H,O+ HsOP@Ei Total Reference Rock or mineral No.

Locality SiO TiO: Al,% Fe,% Fe0 MnO MgG CaO N&,0 KsG H,O+ HsOPs% Total Reference

1. Chemical composition of groundmass and phenocryst samples of dacite and the whole rock samples of granites and basalt

Torihama Kyushu

Kakuto Kyushu

3 Hijiori Yamagata pref.

73.34 0.19 13.03 0.23 0.65 0.06 0.43 1.14 3.33 3.18 3.88 0.30 0.09 9985 1

73,91 0.16 12.36 O”62 0.26 0.00 0.43 1.55 3.27 3.52 2~87 0.80 0.01 99.76 2

71.10 0.25 15.02 0.30 0‘97 0.06 0.10 1.51 2.78 2.87 395 0.25 0.09 100.25 1

1

2

Granite IO Mt. Takakuma Kyushu 73.37 0.43 13.64 0.50 1.16 tr. 0.71 2.05 3.00 3.10 1.29 0.32 0.05 100.42 4

Basalt 11

Dacite 6 4 It0 Ata (Ito) (I) Kyushu Kyushu

7 Ata (II) Kyushu

8

9

Ikeda Kyushu

Osumi Kyushu

68.34 054 14.03 1.28 204 0.14 0.78 2.71 3.27 2.25 4.25 0.10 0.04 9977 1

70.83 0.48 13.47 0.60 1.61 0.09 0.39 1.89 4.14 298 2-70 O-40 0.04 99.62 1

74.02 0.17 12.39 0.46 055 0.06 0.39 1.08 3.55 355 3.25 0.15 0.11 99.73 1

6963 0.53 14.07 0.56 3.26 0.02 1.35 2.98 3.30 3.30 O-60 o-11 0.03 99.74 4

74.26 0.08 12.37 0.82 0.49 0.01 0.20 1.12 3.56 3.30 4.09 0.17 0.01 100.58 3

Plagioclase 8P 4P

Matsura Kyushu

It0 Kyushu

Ikeda Kyushu

Hypersthene 3H Hijiori Yamagata Pref.

52.27 1.47 14.75 2.32 5.97 0.16 7.87 9.30 2.87 1.23 0.68 1.10 0.25 100.20 5

61.89 0.09 2399 0.04 0.27 tr. tr. 8-19 5-14 0.29 0.20 0~00 0.02 100.11 2

60.75 0.02 24.05 0.48 0.16 0.00 o-00 7.69 6.86 0.32 0.33 0.13 0.05 100.84 1

52.03 O-15 l-60 2.19 20.15 1.83 21.14 0.91 0.11 0.09 0.40 0.12 0.16 100.88 1

I. Iv (1970); 2. AFCABUKI (1970)-private 4. SHIBATA (1966); 5. KTJRA~AWA (1970).

communication;

3.

hornblende 3Hb 8Hb Hijiori Yamagata Ikeda Pref. Kyushu 48.99

1.04 6.77 3.27 10.25 0.84 14.88 10.06 l-11 0.22 2.36 0.15 0.18 100*12 1 ARAMAKI

49.45 I-95 5.98 4.15 9.68 0.47 14-03 10.85 1.47 0.39 0.80 0.20 0.07 99.49 1

and Iu (1966);

HIROSHI NAGASAWAand CHARLESC. SOHNETZLER

968

Appendix Mineral Ata* Ikeda* Hijiori* 1tot Torihamat

2. Modal data of phenocrysts for daoites

Quartz

Plagioclase

Hypersthene

Augite

23 19 16 36

81 67 59 78 54

9.4 3.9 4 4 3.6

3.7 1 -

Horn- Magnet- Ilmenblende ite ite 3.0 13 7

* Averaged the data from UI (1970). t UI (1967). 1 Estimated yield of minerals in mineral separation.

5.8

0.2 2.9 5 4 -

Zirconz 3 x lo-”

3 x 10-a 1 x IO-2

Apatite t 1 x IO-1

3 x 10-a 1.5 x 10-Z