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Becker, K., Sakai, H., et al. , 1989Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 111

7. REE, Ba, AN D Sr ABU NDA NCE S A ND Sr, Nd, AN D Ce ISOTOPIC RATIOSIN HOLE 504B BASALTS, ODP LEG 111, COSTA RICA RIFT 1Hiroshi Shimizu, Kouji Mori, and Akimasa Masuda 2

A B S T R A C TAbundances of rare earth elements (REE), Ba, and Sr and isotopic ratios of Sr, Nd, and Ce were determined for sixsamples of basalts drilled at Hole 504B on Leg 111 of the Ocean Drilling Program. Analyses found that these basaltsare the most depleted in Sr, Ba, and light REE among mid-ocean ridge basalts (MORB); Ba depletion is especially notable . On the other hand, Sr, Nd, and Ce isotopic ratios for basalts from Hole 504B are within the range of typical MORBvalues.

I N T R O D U C T I O NS t u d i e s o f r a r e e a r t h e l e m e n t ( R E E ) a b u n d a n c e s a n d N d a n d

S r i s o t o p i c r a t i o s o f m i d - o c e a n r i d g e b a s a l t s ( M O R B ) c o n t r i b u t e t o o u r u n d e r s t a n d i n g o f t h e f o r m a t i o n o f t h e s e r o c k s a n dt h e g e o c h e m i c a l n a t u r e o f t h e m a n t l e f r o m w h i c h M O R B i s d e r ived . Recen t ly , t r ac ing o f Ce i so topes based on the decay o f13 8La to 13 8Ce has been app l i ed to s tud ie s o f the p e t rog enes i sa n d e v o l u t i o n o f t h e E a r t h ' s c r u s t a n d m a n t l e ( T a n a k a a n d M a sud a , 1982 ; Ta naka e t a l . , 1987 , 1988 ; Di ck i n , 1987 a , 198 7b ,1988 ; Dick in e t a l . , 1987 ) . Coup l ing ana ly s i s o f the La -Ce sys t e m w i t h t h e S m - N d s y s t e m s h o u l d b e s i g n i f i c a n t b e c a u s e b o t hp a i r s b e l o n g t o t h e r a r e e a r t h g r o u p . I n t h i s c h a p t e r w e r e p o r tR E E , S r , a n d B a a b u n d a n c e s a n d i s o t o p i c r a t i o s o f Sr a n d N d i nH o l e 50 4 B b a s a l t s , r e c o v e r e d d u r i n g O c e a n D r i l l i n g P r o g r a m( O D P ) L e g 1 11 i n v e s t i g a t i o n s o f t h e C o s t a R i c a R i f t . T h e C ei s o t o p i c r a t i o is r e p o r t e d f o r o n e s a m p l e .

H o l e 5 0 4 B , o f D e e p S e a D r i l l i n g P r o j e c t ( D S D P ) L e g s 6 9 ,7 0 , a n d 8 3 a n d O D P L e g 1 1 1 , i s t h e d e e p e s t s e c t i o n o f b a s e m e n td r i l l e d i n t h e o c e a n c r u s t , i n 5 . 9 - M a c r u s t a b o u t 2 0 0 k m s o u t ho f t h e C o s t a R i c a R i f t . H o l e 5 0 4 B b a s a l t s a r e k n o w n t o b e t h em o s t d e p l e t e d a m o n g M O R B i n i n c o m p a t i b l e e l e m e n t s s u c h a sT h , T a , N a , S r , a n d l i g h t R E E ; h o w e v e r , b a s a l t s m o d e r a t e l y e n r iched in the incompa t ib le e lemen tsa d i f fe ren t magma typew e r e a l s o r e c o v e r e d ( A u t i o a n d R h o d e s , 1 9 8 3 ; M a r s h e t a l . ,1983; E t o u b l e a u e t a l . , 1 9 8 3 ; K e m p t o n e t a l . , 1 9 8 5 ; T u al e t a l . ,1985; E m m e r m a n n , 1 9 8 5 ). L e g 1 1 1 d e e p e n e d H o l e 5 0 4 B b y212 .3 m, to a to ta l dep th o f 1562 .3 m be low sea f loo r (mbsf ) o r1 2 8 7 .8 m i n t o b a s e m e n t . N e w d a t a f or t r a c e e l e m e n t a b u n dances and i so top ic ra t io s f rom th i s sec t ion o f Ho le 504B wi l lh e l p c l a r i f y t h e g e o c h e m i c a l n a t u r e o f t h e d e e p e s t r e c o v e r y o fM O R B .

M E T H O D SSix samples from Hole 504B were analyzed; descriptions of Samples111-504B-143R-1, 22-24 cm, 111-504B-145R-2, 62-64 cm, 111-504B-

148R-1, 83-88 cm, 111-504B-150R-1, 122-123 cm, 111-504B-163R-2,29-31 cm, and 111-504B-169R-1, 102-105 cm, are in Table 1. The rocksrecovered from Hole 504B during Leg 111 are aphyric or sparsely tohighly phyric, fine- to medium-grained olivine tholeiitic basalts. Mostare slightly altered.After acid decomposition of the samples, REE, Ba, and Sr were separated from m ajor elements by an AG50W -X8 resin colum n in HC1 me-

1 Becker, K., Sakai, H., et al., 1989. Proc. ODP, Sci. Results, 111: CollegeStat ion, TX (Ocean Dril l ing Program).2 Laboratory for REE Microanalysis , Department of Chemistry, Faculty ofScience, The Universi ty of Tokyo, Hongo, Tokyo 113, Japan.

Table 1. Descriptions of samples analyzed, Hole 504B,Leg 111 (Shipbo ard Scientific Party, 1988).Core, section,interval (cm) Description

143R-1, 22-24 Moder ately plagioclase-olivine-clinopyrox enephyric basalt145R-2, 62-64 Modera tely clinopyroxene-p lagioclase-olivinephyric basalt148R-1, 83-88 Mode rately plagioclase-clinopy roxene-olivinephyric basal t150R-1, 122-123 Sparsely olivine-clinopyroxene-plag ioclasephyric basal t163R-2, 29-31 Moder ately plagioclase-olivine-clinopyrox enephyric basal t169R-1, 102-105 Mode rately clinopyroxene -olivine-plagioclasephyric basalt

dia. Ce and Nd for isotopic analysis were separated using an AG50W-X8 resin column with a-hydroxy-isobutyric acid . R EE , Sr , and Ba abun dances were determined on a JEOL JMS-05RB mass spectrometer bythe isotope dilu tion method. Isotopic composit ions of Sr and Nd weremeasured on a VG 354 mass spectrometer using three and five Faradaycollectors, respectively. Ce isotopic composition was measured on a VG54-38 double-focusing mass spectrometer. The measured isotopic ratiosof Sr, Nd, and Ce were normalized against 8 6S r/ 88 Sr = 0.1194, 14 6Nd/14 4Nd = 0.7219, and 13 6C e/14 2Ce = 0.01688, respectively. Details ofour Ce isotope measurement are described elsewhere (Makishima et al. ,1987).

Isotopic ratios were measured for the standard salts as follows: 87Sr/86Sr ratio for NBS987 Sr standard was 0.71019 4 (2 am); 14 3N d /1 44 N dratios for La Jolla Nd standard an d for Johnson M atthey N d 2 0 3(JMC321, batch no. S.810931A) were 0.511823 16 and 0.511080 12, respectively; and 13 8C e/14 2Ce ratio for Johnson Matthey Ce0 2(JMC 304) was 0.0225775 14. Ou r 1 43 N d / 14 4Nd ratios for both LaJolla s tandard and Johnson M atthey N d 2 0 3 exhibit slightly lower valuesthan those reported by O'Nions et al. (1977), Jahn et al. (1980), Lug-mair et al. (1983), and Bell and Blenkinsop (1987) (Table 2).In plott ing chondrite-normalized REE, Sr, and Ba abundances, alinear scale as well as a logarithmic scale was used for the ordinate axis,following Shimizu et al. 's (1980) strategy for distinguishing REE patterns of abyssal tholeiites. Masuda (1979) explained the advantage andtheoretical significance of linear scale plotting for solid-type igneousrocks or potentially for the conjugate relationship between the solid-and liquid-type rocks, based on the model originally presented by Masuda and Matsui (1966) and further developed by Masuda. In Masuda's(1979) model, the basic evolutionary framework for the REE patterns ofwhole-rock samples of com mon igneous rocks is determined by the solidification process, starting from melt with a chondritic REE abundance ratio as a linear bulk-partition coefficient function. Thus, for incipient solid-phase REE patterns, using a linear scale for the verticalaxis is advantageous in demonstrating rectilinearity, whereas a logarithmic scale is significant for plotting liquid-type material systems.

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H. SHIMIZU, K. MOR I, A. MASUDATable 2. Comparison of 14 3Nd/ 14 4Nd ratios for Nd standard salts.

La Jolla standard JMC 321 N d 2 0 3This study 0.511823 0.000016 0.511080 0.000012Lugm air et al. (1983) 0.511858 + 0.000004 Bell and Blenk insop (1987) 0.51186 + 0.00002 O'N ions et al. (1977) 0.51112 0.00003Jahn et al. (1980) 0.511137 0.000008Note: Errors are 2a m . The 1 4 3N d / 1 4 4 Nd ratio by Lugmair et al. (1983) was normalized against 1 4 8N d / 1 4 4 Nd = 0.241572, and the 1 4 6N d / 1 4 4 Nd correspondingly obtaine d was 0.721878 0.000007 for the La Jolla Nd standard. The Nd isotopic ratios from O'Nions et al. (1977), Jahn et al. (1980),Bell and Blenkinsop (1987), and this study were normalized against 1 4 6N d /14 4Nd = 0.7219.

R E S U L T S A N D D I S C U S S I O NR E E , Ba, an d S r Ab u n d an ces

REE, Sr, and Ba abundances for four samples are lis ted inTable 3 and presented on chondrite-norm alized p atterns (M a-suda-Coryell plot; M asud a, 1962; Coryell et al., 1963) in Figure1. The depletion of Ba (0.70-0.89 ppm) is remarkable. Ba abundance in oceanic tholeiitic basalts ranges from several to severalhundred parts per million and averages 14.5 ppm in Puchelt 's(1972) list of Ba concentration in terrestrial rocks. Similar typical Ba abundances of 12.2 ppm for Type I MORB and 55 ppmfor Type II M OR B are reported by the Basaltic Volcanism S tudyProject (1981). In comparison to Bryan et al.'s (1976) classification, Type I corresponds to basalt erupted along the no rm altopographic section of mid-ocean ridges and Type II corresponds to basalt produced at elevated sections of mid-oceanridges adjacent to volcanic platforms associated with oceanic islands. Sr abundances in the Hole 504B basalts are also low (54-61 ppm), but are not as depleted as Ba abundances. Faure(1986) reported Sr abundances ranging from 96 to 154 ppm foroceanic tholeiites from the Pacific Ocean. The average Sr concentrations summarized by the Basaltic Volcanism Study Pro j ect (1981) are 127 and 105 ppm for Type I and Type II MORB,respectively.(La /Sm) N values around 0.3 for Hole 504B samples (Table 3)are lower than the 0.4-0.7 values of MORB from the corresponding normal ridge segment (Sun et al., 1979), suggestingTable 3. REE, Ba, and Sr abundances (ppm) in Hole 504B basalts.

Sample

ElementLaCeNdSmEuGdDyErYbLuBaSr

143R-1,22-24 cm1.1774.595.442.270.8423.514.512.912.860.4310.88756.5

145R-2,62-64 cm1.0233.984.711.950.7272.953.792.442.310.3380.69554.4

148R-1,83-88 cm1.234.975.982.390.9213.734.743.083.010.4530.76859.7

163R-229-31 cm1.0864.445.362.250.8093.354.362.742.650.3590.70561.3

Normalizingvalue30.3780.9760.7160.2300.08660.3110.3900.2550.2490.03874.2111.1

Ratios between chrondrite-normalized values( L a / Sm ) N 0.316 0.319 0.313 0.294( Ce / Y b ) N 0.409 0.440 0.421 0.428a Normalizing values for REE and Ba are from abundances of these elements inLeedey chondri te (Masuda et al ., 1973; Naka mura a nd M asuda, 1973). Thenormalizing value for Sr, 11.1 ppm, is from Gopalan and Wetherill (1971).

strong depletion of light REE in the Hole 504B basalts . Sr andBa abundances increase with increasing (La/Sm)N values andthe Hole 504B basalts fall in the lowest value ranges (Figs. 2 and3). The chondrite-normalized REE patterns of four samplesfrom Hole 504B are similar to each other, with some variationof fine structures in heavy RE E span (Fig. 4). Generally, La, Ce,and Nd plot along a straight line, but Ce has a positive deviation from a La-Ce-Nd regression line whereas La and Nd deviate in a negative direction. (From a theoretical viewpoint, thesedeviations indicate an expected slight curvature.) REE patternsof basalts from Holes 417A and 417D (D SDP Leg 51, the Bermuda Rise; Shimizu et al., 1980) have the same features as observed for the Hole 504B La-Ce-Nd span. In plots of Samples111-504B-143R-1, 22-24 cm, and 111-504B-148R-1, 83-88 cm,Gd, Dy, Er, and Yb appear to fall along a straight horizontalline, whereas heavy REE for Samples 111-504B-145R-2, 62-64cm, and 111-504B-163R-2, 29-31 cm, show slightly curved features with a maximum at Dy.

S r , Nd , an d Ce I sot op ic Rat iosThe isotopic ratios of Sr, Nd, and Ce listed in Table 4 are essentially unaffected by alteration. 87Sr/86 Sr ratios for five samples from this study are between 0.7024 and 0.7028, with a

mean of 0.70266. A similar value of 0.70266 was reported as amean 87Sr/ 86 Sr ratio for the Hole 504B basalts recovered from330 to 560 m within basement during Legs 69 and 70 (Barretand Friedrichsen, 1982; Barret, 1983), which is almost identicalto the average isotopic value of fresh MORB. On the otherhan d, Barret and Friedrichsen (1982) and B arret (1983) foundhigher 87Sr/ 86 Sr ratio s, with a mean o f 0.70320, in samples fromthe upper 260-m interval within basement at Hole 504B, andthey interpreted these higher ratios in terms of strontium-isotope alteration during basalt-seawater interaction. Furthermore,for the Hole 504B basalts in the 580-1075-m interval withinbasement (Leg 83), higher and scattered 87S r/ 86 Sr ratios between0.7025 and 0.7068 and with a mean of 0.7038 were reported byFriedrichsen (1985). Based on strontium, oxygen, and hydrogenisotopic compositions, Friedrichsen (1985) suggested the existence of a seawater/crust interface, now at a depth of 620 mwithin basement, during high-temperature water-rock interact ions . The 87S r/ 86 Sr ratios obtained from our investigation havean average value similar to that for fresh MORB, suggestingthat basalts in the 1075-1287-m interval within basement haveundergone lit t le alteration.

T he 14 3N d/14 4Nd and 87Sr/86 Sr ratios of the Hole 504B basalts are similar to those reported for oceanic basalts from thePacific, including the East Pacific Rise and Juan de Fuca andGalapagos ridges (Fig. 5) (Cohen et al., 1980; White and Hof-mann, 1982). The similarity of the I4 3N d/ 14 4Nd a nd 13 8Ce/142 Ce ratios of Sample 111-504B-143R-1, 22-24 cm , to MO RBrat ios from the Mid-Atlant ic Ridge (2259.14 'N, 4330.39 'W,and 2302.63 'N, 4501.05 'W) and Eas t Pac if ic Rise (1252 'S,1157'W) (Tanaka et al., 1987) is evident in Figure 6.Although a limited number of isotopic ratios were determined in this study, the Sr, Nd, and Ce isotopic ratios for Hole504B basalts are within the range of typical M OR B values. W ithrespect to the trace element abundances, however, high depletion of incompatible elements in the Hole 504B basalts is nottypical of MORB.

I sot op ic Evolu t ion of NdThe isotopic evolution of Nd from Hole 504B basalts and depleted mantle relative to chondritic uniform reservoir (CHUR)is shown in Figure 7. Present-day CHUR values are 14 3N d/14 4N d= 0.512638 and 14 7Sm /14 4Nd = 0.1966 (Wasserburg et al.,1981). Two sets of corresponding values for present-day de-

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Sr Ba La Ce Nd Sm Eu Gd Dy Er Yb LuFigure 1. Chondrite-normalized (logarithmic scale) REE-Ba-Sr patterns of Hole 504B basalts (Samples 111-504B-143R-1, 22-24 cm, 111-504B-145R-2, 62-64 cm, 111-504B-148R-1, 83-88 cm, and111-504B-163R-2, 29-31 cm ). Normalizing values for REE and Ba are from abundan ces of these elements in Leedey chondrite (Masuda et al., 1973; Nakamura and Masuda, 1973). The normalizingvalue for Sr, 11.1 ppm, is from Gopalan and Wetherill (1971).

pleted mantle were chosen for average MORB; the first set ofparameters for depleted mantle (DM-A) is 14 3N d/14 4Nd = 0.5131(e Nd = +9.0 ) and 14 7Sm /14 4Nd = 0.2238 (Haw kesworth andvan Calsteren, 1984) and the second set (DM-B) is 14 3N d/14 4N d= 0.513153 (eN d = + 10.0) and 14 7Sm /14 4Nd = 0.225 (Liew andMcCulloch, 1985).One of the simplest interpretations of the Nd isotopic ratiosof the H ole 504B basalts is that the basalts were generated fromCHUR with the same Sm/Nd ratios as the samples at ages in

the CH UR model of 1.4 x I0 9to 1.7 x I09 yr (Table 5 and Fig.7) . Another, more likely interpretation is that these basalts werederived from depleted mantle sources with a Sm/Nd ratio closeto average MORB and subsequently experienced further depletion in incompatible elements. Redepletion occurred between200 and 600 Ma for DM-A, with 14 3N d/14 4Nd = 0.5131 (eNd =+ 9.0) and 14 7Sm /14 4Nd = 0.2238 (Hawkesworth and van Calsteren, 1984), whereas redepletion is younger than 365 Ma forDM-B, with 14 3Nd/14 4Nd = 0.513153 (eNd = +10.0) and

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H. S HIMIZU, K. MORI , A . MAS UDA

0.8

0.6

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Figure 2 . (La/Sm) N vs. Ba concentra t ion for MORB. Open circ les =Legs 2 and 3, Atlantic Ocean floor (Frey et al. , 1974); triangles = Mid-Atlantic and Mid -Indian ridges (Sun et al. , 1979); crosses = Holes417A and 417D and Mid-Atlantic Ridge (Shimizu et al. , 1980); solid circles = Hole 504B (this study).

400Sr (p p m)Figure 3 . (La/Sm) N vs. Sr concentra t ion for MORB. Symbols same asfor Figure 2.1 4 7 S m / 1 4 4 Nd = 0 .225 (Liew an d M cC ul l oc h , 1985) . In the la t t e rc a s e , t h e r e d e p l e t i o n p r o c e s s m a y b e r e l a t e d t o a f o r m a t i o n s e r i e s o f b a s a l t s . A p r o b a b l e m e c h a n i s m w o u l d b e a l i m i t e d p a r t i a l - m e l t i n g e ve n t j u s t p r i o r t o b a s a l t f o r m a t i o n ( i . e . , a p r e c u r s o r y p a r t i a l m e l t i n g ) . F o r e i t h e r s c e n a r i o , t h e s o u r c e s o f t h eH o l e 5 0 4B b a s a l t s w e r e p r o b a b l y d e r i v e d f r o m d e p l e t e d m a n t l ea n d u n d e r w e n t f u r t h e r d e p l e t i o n in i n c o m p a t i b l e e l e m e n t s . T h i sm o d e l w o u l d s a t i s f a c t o r i l y e x p l a i n t h e i s o t o p i c a n d a b u n d a n c ed a t a f o r t h e H o l e 5 0 4 B b a s a l t s o f S r , N d , a n d C e i s o t o p i c r a t i o s

wi th typ ica l va lues o f M O R B b u t w i t h f u r t h e r d e p l e t i o n o f i n c o m p a t i b l e e l e m e n t s .

C O N C L U S I O N ST h e b a s a l t s f r o m H o l e 5 0 4 B a r e t h e m o s t d e p l e t e d i n S r , B a ,

a n d l ig h t R E E a m o n g M O R B . S t r o n g d e p le t i o n o f R E E i s s u g g e s t e d b y ( L a / S m ) N r a t i o s a r o u n d 0 . 3 i n t h e H o l e 5 0 4 B b a s a l t s ,w h i c h a r e l o w e r t h a n t h e c o r r e s p o n d i n g v a l u e s o f 0 . 4 - 0 . 7 f o rM O R B f r o m n o r m a l r i d g e s e g m e n t s . B a a b u n d a n c e s a r e e x t r e m e l y l o w ( 0 . 7 - 0 . 9 p p m ) , b u t t h e i s o t o p i c r a t i o s o f S r , N d ,a n d C e f o r H o l e 5 0 4 B b a s a l t s a r e w i t h i n t h e r a n g e o f t y p i c a lM O R B r a t i o s . T h e s e d a t a a r e e x p l a i n e d b y a m o d e l o f b a s a l tf o r m a t i o n f r o m s o u r c e s d e p l e t e d i n i n c o m p a t i b l e e l e m e n t s ,s u c h a s a v e r a g e M O R B , t h a t u n d e r w e n t f u r t h e r d e p l e t i o nc a u s e d b y a p r e c u r s o r y e p i s o d e o f l i m i t e d p a r t i a l m e l t i n g .

ACKNOWLEDGMENTSWe thank Dr. T. Tanak a, Geological Survey of Jap an , for Ce and N disotopic standard solutions and Dr. S. Nakai, the University of Tokyo,for his help in the experiments. This research was supported by a grant-in-aid for scientific research from the Ministry of Education, Scienceand Culture of Japan.

REFERENCESAutio , L. K., and Rh odes, J. M., 1983. Cost a Rica Rift zone basa lts:geochemical and experimental data from a possible example of multistage melting.I n Cann, J . R. , Langseth , M. G. , Honnorez, J . , VonHerzen, R. P., White, S. M., et al. , Init. Repts. DSDP, 69: Washington (U.S. Govt. Printing Office), 729-745.Barrett, T. J., 1983. Strontiu m- and lead-isotope com position of somebasalts from Deep Sea Drilling Project Hole 504B, Costa Rica Rift,Legs 69 and 70.In Cann, J . R. , Langseth , M. G. , Honnorez, J . , VonHerzen, R. P., White, S. M., et al. , Init. Repts. D SDP, 69: Washington (U.S. Govt. Printing Office), 643-650.Barrett, T. J., and Friedrichsen, H., 1982. Strontium and oxygen isotopic composition of some basalts from Hole 504B, Costa Rica Rift,DSDP Legs 69 and 70.Earth Planet. Sci. Lett., 60:27-38.Basaltic Volcanism Study Projec t, 1981. Ocean-flo or bas altic volcan-ism. In Basaltic Volcanism on the Terrestrial Planets: New York(Pergamon), 132-160.Bell, K., and Blenk insop, J., 1987. Arch ean depleted m antle : evidencefrom Nd and Sr initial isotopic ratios of carbonatites. Geochim.Cosmochim. Acta, 51:291-298.Bryan, W B., Tho mp son , G , Frey, F. A. , and Dickey, J. S., 1976. Inferred settings and differentiation in basalts from the Deep Sea Drilling Project. J. Geophys. Res., 81:4285-4304.Cohen, R. S . , Evensen, N. M., Hamilton, P . J . , and O'Nions, R. K. ,1980. U-Pb, Sm-Nd and Rb-Sr systematics of mid-ocean ridge basalt glasses.Nature, 283:149-153.Coryell, C. D., Ch ase, J. W , and W inchester, J. W., 1963. A pro cedurefor geochemical interpretation of terrestrial rare-earth abundancepatterns. J. Geophys. Res., 68:559-566.Dickin, A. P., 1987a. Cerium isotope geochemistry of ocean island basalts.Nature, 326:283-284., 1987b. La-Ce dating of Lewisian granulites to constrain the13 8La /3-decay half-life. Nature, 325:337-338., 1988. Mantle and crustal Ce/Nd isotope systematics. Nature,

333:403.Dickin , A. P . , Jones, N. W, Thirwall , M. F , and Thom pson, R. N . ,1987. A Ce/Nd isotope study of crustal contamination processes affecting Palaeocene magmas in Skye, northwest Scotland. Contrib.Mineral. Petrol., 96:455-464.Emm erman, R. , 1985. Basement geochemistry , Hole 504B. In Anderson, R. N., Honnorez, J., Becker, K., et al. , Init. Repts. D SDP, 83:Washington (U.S. Govt. Printing Office), 129-164.Etoubleau, J . , Corre , O. , Joron, J . L. , Bougault , H. , and Treuil , M. ,1983. Costa Rica Rift: variably depleted basalts in the same hole. InCann, J . R. , Langseth , M. G. , Honnorez, J . , Von Herzen, R. P . ,White , S . M. , e t a l . , Init. Repts. D SDP, 69: Washington (U.S. Govt.Printing Office), 765-773.Faure, G., 1986.Principles of Isotope Geology: New York (Wiley).

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REE, Ba , AND Sr ABUNDANCES AND Sr , Nd, AND Ce ISOTOPIC RATIOS INHOLE 504B BASALTSFrey, F. A., Bryan, W. B., and Thompson, G., 1974. Atlantic Oceanfloor: geochemistry and petrology of basalts from Legs 2 and 3 ofthe Deep Sea Drilling Project. J. Geophys. Res., 79:5507-5527.Friedrichsen, H. , 1985. Stron tium, oxygen, and hydrogen isotope studies on primary and secondary minerals in basalts from the CostaRica Rift , Deep Sea Drilling Project Hole 504B, Leg 83. I n Anderson, R. N., Honnorez, J., Becker, K., et al ., Init. Repts. D SDP, 83:Washington (U.S. Govt. Printing Office), 289-295.Gopalan, K., and Wetherill, G. W., 1971. Stron tium. In Mason, B.(Ed.) ,Handboo k of Elemental Abundances in Meteorites: New York

(Gordon and Breach), 297-302.Hawkesworth, C. J., and van Calsteren, P.W.C., 1984. Radiogenic isotopes: some geological applications. In Henderson, P. (Ed.), RareEarth Element Geochemistry: A mster dam (Elsevier), 375-421.Jahn , B. M., Griffi ths, J . B. , Chariot , R. , C ornichet , J . , and Vidal , F ,1980. Nd and Sr i sotopic composi t ions and REE abundance s of Cretaceous MORB (Holes 417D and 418A, Legs 51, 52 and 53). EarthPlanet. Sci. Lett., 48:171-184.Kempton, P. D., Autio, L. K., Rhodes, J. M., Holdaway, M. J., Dun-gan , M. A., and Jo hns on, P., 1985. Petrology of basalts from H ole504B, Deep Sea Drilling Project, Leg 83.In Anderson , R . N . , Honnorez, J., Becker, K., et al.,Init. Repts. D SDP, 8 3: Wash ington (U.S.Govt. Printing Office), 129-164.Liew, T. C , and McCu lloch, M. T, 1985. Genesis of granitoid bath o-liths of peninsular Malaysia and implications for models of crustalevolution: evidence from a Nd-Sr isotopic and U-Pb zircon study.Geochim. Cosmochim. Acta, 49:587-600.Lugmair, G. W., Shimam ura, T , Lewis, R. S., and And ers , E., 1983.Samarium-146 in the early solar system: evidence from neodymiumin the Allende meteorite. Science, 222:1015-1018.Makishima, A., Shimizu, H., and Masuda, A., 1987. Precise measurement of cerium and lanthanum isotope rat ios. Mass Spectrosc, 35:64-72.Marsh, N. G., Tarney, J., and Hendry, G. L., 1983. Trace element geochemistry of basalts from Hole 504B, Panama Basin, Deep SeaDrilling Project Legs 69 and 70. In Cann , J. R. , Langseth, M. G ,Honnorez, J. , Von Herzen, R. P. , Whi te, S. M., et al . , Init. Repts.DSDP, 69: Washington (U.S. Govt. Printing Office), 747-763.Masuda, A., 1962. Regularities in variation of relative abundances oflanthanide elements and an attempt to analyse separation index patterns of some minerals. J. Earth Sci. Nagoya Univ., 10:173-187., 1979. Effects of l inear bulk partit ion coefficient functions ofREE: liquid-type and solid-type patterns as a basic framework. J.Earth Sci. Nagoya Univ., 26/27:75-92 .Mas uda, A ., and Matsu i, Y., 1966. The difference in lanthanid e abu ndance pattern between the crust and the chondrite and its possiblemeaning to the genesis of crust and mantle. Geochim. Cosmoch im.Acta, 30:239-250.Masuda, A., Na kamu ra, N. , and Tanaka, T, 1973. Fine structures ofmutual ly normal ized rare-earth pat terns of chondri tes. Geochim.Cosmochim. Acta, 37:239-248.

Nakam ura, N. , and Masu da, A ., 1973. Chondri tes with pecul iar rare-earth pat terns. Earth P lanet. Sci. Lett., 19:429-437.O'Nions, R. K., Hamilton, P. J., and Evensen, N. M., 1977. Variationsin 1 43N d/ 14 4Nd and 8 7S r/ 86 Sr ratios in oceanic basalts.Earth Planet.Sci. Lett., 34:13-22.Puchel t , H. , 1972. Barium. In Wedepohl , K. H. (Ed.), Handbook ofGeochemistry: Berlin (Springer-Verlag).Shimizu, H., Masuda, A., and Ui, T., 1980. Determination of rare-earth elemen ts in Leg 51, Site 417 samples. In Donnel ly, T, Franche-teau, J., Bryan, W , Ro binson , P., Flower, M ., Salisbury, M. , et al .,Init. Repts. DSDP, 51, 52, 53, Pt . 2: Washington (U.S. Govt . Print ing Office), 1 113-1120.

Shimizu, H., Nakai, S., Tasaki, S., Masuda, A., Bridgwater, D., Nut-man, A. P. , and Baadsgaard, H. , 1988. Geochemist ry of Ce and Ndisotopes and REE abundances in the Amitsoq gneisses, West Greenl and . Earth Planet Sci. Lett., 91:159-169.Shimizu, H., Tanaka, T , a nd Mas uda, A ., 1984. Meteori tic 1 38C e/ 14 2C eratio and its evolution. Nature, 307:251-252.Shipboard Scientific Party, 1988. Site 504. In Becker, K., Sakai, H., etal., Proc. ODP, Init. Repts., I l l : College Stat ion, TX (Ocean Dri l ling Program), 35-251.Sun, S. S., Nesbitt , R. W., and Sharas kin, A. Y , 1979. Geochem icalcharacteristics of mid-ocean ridge basalts.Earth Planet. Sci. Lett.,44:119-138.Tanaka, T, and Masu da, A., 1982. The La-Ce geochronometer: a newdat ing method. Nature, 300:515-518.Tanaka, T , Shimizu, H., Kawata, Y , and Mas uda, A., 1987. CombinedLa-Ce and Sm-Nd isotope systematics in petrogenetic studies. Na -ture, 327:113-117., 1988. Mant le and crustal Ce/N d isotope systemat ics. Nature,333:404.Tual , E. , Jahn, B. M., Bougaul t , H. , and Joron, J. L. , 1985. Geochemistry of basalts from Hole 504B, Leg 83, Costa Rica Rift . In Anderson, R. N., Honnorez, J., Becker, K., et al ., Init. Repts. D SDP, 83:Washington (U.S. Govt. Printing Office), 201-214.Wasserburg, G. J. , Jacobsen, S. B. , DePaolo, D. J. , McCul loch, M. T ,and Wen, T, 1981. Precise determinat ion of Sm/N d rat ios, Sm andNd isotopic abundances in standard solut ions. Geochim. Cosmo-chim. Acta, 45:2311-2323.White, W. M., and Hofmann, A. W., 1982. Sr and Nd isotope geochemistry of ocean basalts and mantle evolution. Nature, 296:821-825.

Ms 111B-123Date of initial receipt: 25 April 1988Date of acceptance: 8 August 1988

Table 4. Sr, Nd, and Ce isotopic compositions in Hole 504B basalts.Core, sect ion,interval (cm) ' S r / 8 0 S r 3 N d / 1 4 4 N d M a 8 C e / , 4 Z Ce 143R- 1, 22-24145R- 2, 62-64148R-1, 83-88150R- 1, 122-123163R- 2, 29- 31169R- 1, 102- 105

0. 70247 0. 000010. 70271 0. 000040. 70257 0. 000020. 70283 0. 000060. 70272 0.00001

0. 513141 0. 0000060. 513102 0. 0000070. 513115 0. 0000060. 513187 0. 000005

( + 9.8)( + 9.1)( + 9.3)(-)( + 1 0 .7 )(-)

0.0225689 + 0.0000036

Note: Errors are 2a m .3 *Nd = ([Rsample R C H U R ] / R C H U R ) X 14; R = 1 4 3N d / 1 4 4 Nd and ( 1 4 3 N d / 1 4 4 N d ) C H U R =0.512638.b Value recalculated by normalization of 1 3 8C e / 1 4 2 Ce = 0.0225762 for JM C3 04 Ce standard (Makishima et al., 1987).

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H. SHIMIZU, K . MORI, A . MASUDA

1 4 3 R - 1

Yb LuFigure 4. Chondrite-normalized (linear scale) REE patterns of Hole 504B basalts (Samples 111-504B-143R-1, 22-24 cm, 111-504B-145R-2, 62-64 cm, 111-504B-148R-1, 83-88 cm, and 111-504B-163R-2, 29-31 cm).

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REE, Ba , AND Sr ABUNDANCES AND Sr , Nd, AND Ce ISOTOPIC RATIOS INHOLE 504B BASALTS:Nd

0.5135

0.5130

0.5125

_

~ ^ ^ ^

i . , , .

10

0.7020 0.7025 0.7030 0.703587 S r / 8 6 S r

Figure 5. l4 3N d / 1 4 4 Nd vs . 87S r/86 Sr for Paci fic Ocean MORB. Squares= Juan de Fuca Ridge, Galapagos Ridge, and East Paci fic Rise (Cohenet al., 1980); triangles = East Pacific Rise (Wh ite and Ho fm ann , 1982);solid circles = Hole 504B (this study). The line shows the trend forMORB.

:Ce- 3

0.5134

0.5132

0.5130

0.5128

0.5126

10

0.02256 0.02257138 Ce / K 2 CeFigure 6. 1 43 N d / 14 4Nd vs . 13 8C e /14 2Ce for MORB. Solid circle = Hole504B basalt (this study); open circle basa lt from E ast Pacific Rise(1252 'S , 110 57'W ; Tanaka et al ., 1987); open triangles = basaltsfrom Mid-At lant ic Ridge (2259.14'N, 4330.90'W and 2302.63'N,4501.05 'W; Tanaka et al . , 1987). e = ([R s a m p l e - RC H U R ] / R C HUR ) *I0 4, where Rs a m p ie is the sample isotopic ratios 1 43 N d / 14 4 Nd or 1 3 8Ce/14 2Ce and RC H U R *Schon dritic uniform reservoir. Present-day values of( i 4 3 N d / i 4 4 N d ) C H ( jR a n d ( i 38C e / i 42Ce) C H U R are 0.512638 (Wasserburg etal., 1981) and 0.022572 2 (Shimizu et al., 1984, 1988), respectively.

504 BBASALTS

CHUR

Time IGalFigure 7. Isotopic evolution of Nd in average MORB (dashed lines) andHole 504B basalts (solid lines) (see text and Table 5). Depleted m antle A(DM-A) has present-day values of i 4 3N d / 1 4 4 Nd = 0.5131 (e N d = +9 .0)an d 14 7S m /14 4Nd = 0.2238 (Hawkesworth and van Calsteren, 1984).Depleted mantle B (DM-B) has present-day values of 14 3N d /1 4 4 Nd =0.513153 (eNd = +10 .0) and 14 7S m /1 44 Nd = 0.225 (Liew and McCulloch, 1985). CHUR (horizontal l ine) present-day values are 14 3N d / 1 4 4 N d= 0.512638 and 1 47 S m / 14 4 Nd = 0.1966 (Wasserburg et al ., 1981).ewT) = ([Rs a m p l e(T) - RC H U R ( T ) ] / R C H U R ( T ) ) X I04 ; R(T) = l 4 3N d /14 4Nd at t ime T.

Table 5. Nd model ages for chondritic uniform reservoir (CHUR) and depleted mantle (DM-A and DM-B).Core, section,interval (cm) CHURa DM-Ab DM-BC143R-1,145R-2,148R-1,163R-2,

22 2462 6483 8829-31

1.47 x1.41 x1.72 x1.55 x

10 yI0 9I0 9I0 9

0.4090.2120.4240.618

x 10* 0.129 x 10*x I0 9 x I0 9 x I0 9 0.365 x I09Note: In calculating Nd model ages, the Nd isotopic ratios ofthe Hole 504B basalts are corrected by normalization of143Nd/144Nd = 0.511858 for the La Jolla Nd standard.\a 14 7Sm = 6.54 x 10-12 /yr.a Present-day parameters: 14 3Nd/ 14 4Nd = 0.512638 and14 7Sm /14 4Nd = 0.1966 (Wasserburg et al., 1981).b Present-day parameters: 14 3N d/ i4 4Nd = 0.5131 (e Nd =

+ 9.0) and 14 7Sm /14 4Nd = 0.2238 (Hawkesworth and vanCalsteren, 1984).cPresent-day parameters: 14 3Nd/ 14 4Nd = 0.513153 (e Nd =+10.0) and 14 7Sm /14 4Nd = 0.225 (Liew and McCulloch,1985).

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ree and sr abudance in basalts

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