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Rare-earth elements in basalt samples, Gulf of California
Chemical Geology, 26 (1979) 267--275 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
267
RARE-EARTH ELEMENTS IN BASALT SAMPLES, G U L F OF CALIFORNIA
D A V I D J. T E R R E L L , S U R E N D R A
PAL, M A R G A R I T A
L O P E Z M. and JOSE PI~REZ R.
Instituto de Geoffsica, Universidad Nacional Aut6noma de M$xico, M~xico 20, D.F.
(M~xico) (Received July 10, 1978; revised and accepted February 6, 1979)
ABSTRACT Terrell,D.J.,Pal, S., L6pez M., M. and P~rez R., J., 1979. Rare-earth etements in basalt samples, Gulf of California.Chem. Geol., 26: 267--275.
Results are given o f chemical analyses and rare-earth e l e m e n t s o f glass rims, crystalline interior (core) and altered exterior (margin) of three pillow basalts from the mouth of the Gulf of California. A notable alteration effect of low-temperature weathering s e e m s to he a loss of rare-earth e l e m e n t s f r o m basalt.
INTRODUCTION After an initial geochemical and petrographic study of three samples dredged from the m o u t h of the Gulf of California (LSpez M. et al., 1978), it was t h o u g h t to be o f some importance to investigate low-temperature alteration effects (halmyrolysis) on the chemistry of these samples. The rock fragments showed obvious macroscopic zoned color differences related to weathering (Fig.l); these different zones were sampled and analyzed for major elements, H20, COs and rare-earth elements (REE). Thus following S.R. Hart et al. {1974), the samples were split into three fractions: glass sampled from the surface of some pillow fragments, core sampled from a "fresh appearing" interior part of pillow fragments, and margin from presumably weathered brownish or grayish outer zone o f the fragments. The pillow fragments left from DH-08 (Fig.l) after the earlier study by LSpez M. et al. (1978) contained no glass. Thin glassy rims were present in some fragments from this site but were used up in the previous study by LSpez M. et al. (1978). ANALYTICAL METHODS For major-element chemistry a combination of classical and instrumental methods was used. Thus SiO2 and H20- were determined by gravimetry;
268
Fig.1. Basalt fragments from DH-08 showing zoned color differences. COs by the method of Shapiro and Brannock (1962); H20 ÷ by difference in loss on ignition (LOI) and CO2; A1203, total Fe (as Fe203), MnO, MgO and CaO by atomic absorption spectrometry; Na20 and K20 by flame p h o t o m e t r y ; TiO2 and P2Os by colorimetry and finally FeO (ferrous iron) by volumetry. Precisions and accuracies range between 1 and 5%. REE were measured by spark source mass spectrometry following the method of Nicholls et al. (1967). Precisions and accuracies for REE vary between 10 and 30%. RESULTS AND DISCUSSION The locations of the analyzed samples have been given by L6pez M. et al. (1978). Sample DH-01 is from the eastern flank of East Pacific rise crest, DH-12 from the southern flank of a seamount and DH-08 is from the first major slope of continental borderland. Their major-element chemistry is given in Table I. Abundances of some major elements are plotted in Fig.2. The REE contents of these samples are presented in Table II and plotted in Fig.3. The chondrite values for normalization are those for the Leedey chondrite (Masuda et al., 1973; Masuda, 1975). Presumably the quenched glass best represents the liquid composition at the time of eruption and can be used to classify the samples. Both DH-01 and and DH-12 can be classified as tholeiitic basalts as both of them fall in the tholeiitic field of Na20+K20 vs. SiO2 diagram of MacDonald and Katsura (1964). As stated earlier, no glass could be analyzed for DH-08. However,
0.40
0.41
F e O T = total iron as FeO.
FeO T + MEO
11.02
10.87
Total Fe as Fe~O3
100.01
99.82
Total
49.61 1.38 15.90 3.68 6.60 6.63 12.12 0.21 2.08 0.28 0.12 0.07 0.47 0.75 0.11
50.10 1.34 15.58 3.04 7.04 6.81 11.95 0.18 2.28 0.31 0.12 0.07 0.30 0.60 0.10
SiO~ TiO 2 A1203 Fe20 , FeO MgO CaO MnO Na20 K20 P20~ Cr203 H~O" H20 ÷ CO 2
0.38
11.31
100.04
49.39 1.31 15.74 4.77 5.88 6.16 11.85 0.38 2.19 0.37 0.12 0.07 0.67 0.97 0.17
0.46
10.08
99.06
48.47 1.63 16.83 2.28 6.80 7.70 10.52 0.21 2.80 0.35 0.17 0.06 0.38 0.76 0.10
glass (g)
margin (m)
glass Og)
core (e)
DH-12
DH-01
Major-element chemistry of the basalt samples
TABLE I
0.46
9.81
99.60
49.66 1.33 15.52 2.42 7.24 7.52 12.07 0.17 2.23 0.26 0.12 0.07 0.24 0.65 0.10
core (c)
0.35
9.32
100.06
48.85 1.78 17.77 4.81 3.51 4.56 11.82 0.12 3.10 0.34 0.17 0.06 1.31 1.66 0.20
margin (m)
0.43
10.85
99.45
48.88 1.69 15.60 2.50 7.50 7.38 11.97 0.17 2.17 0.27 0.16 0.06 0.16 0.84 0.10
core (c)
DH-08
0.40
11.57
99.95
48.94 1.66 15.54 3.42 7.32 7.08 11.94 0.16 2.24 0.33 0.16 0.06 0.27 0.70 0.13
margin (m)
t~ O~ ¢.P
270 50
4O /
40
CN ,.2
3D
/
/
I
,
o
o~
30
o
20
?
s
/
iI
I0
20
/ I ~"
o
!
o
I0
I
8O
o
~.
I
04
~'--A
o
~\
60
%
40
~
0.3
o
02i
-.f
OI
20
0
i
L
DH-OI
'
'
DH-12
'
'
DH-08
I
DH-OI
I
I
DH-12
,
DH-08
Fig.2. Behavior of some major elements during sea-floor weathering of pillow basalts (g, c a n d m stand for glass, core and margin, respectively).
both the core and the margin samples from DH-08 fall well within the tholeiitic field of Na20+K20 vs. SiO2 plot. Our results on the effects of low-temperature alteration of oceanic basalts are summarized and compared or contrasted with the findings of other workers in Table III. Thus based on major-element analyses, the rocks from the Gulf of California show an increase in Fe 3+, H2 O, CO2 and K upon alteration, a decrease in Mg and Fe 2+ and a practically constant content of Cr. As can be seen from Table III these observations are consistent with the results of most workers. A point worth noting is rather similar H20 contents of the core and the margin for DH-08. This implies that either H20 is not a good indicator of alteration or the interior of DH-08 is also considerably altered. The second possibility is supported by REE data. The most important result of the present study seems to be a loss in REE contents of basalt following alteration. This observation seems to disagree with other workers. Thus Frey et al. (1968) found that REE abundances in altered basalts are not distinctly different from those in fresh basalts and concluded that REE are not affected by the initial alteration effects caused by seawater. Philpotts et al. (1969) showed that REE apparently remain constant upon alteration. Christensen et al. (1973} have concluded that heavy REE (HREE) are least affected by halmyrolysis. However, Thompson (1973) has shown that REE, particulm'!y the light REE (LREE), increase in the altered interiors. Condie (1976) based his work on the observation that the REE are among the trace elements that are most resistant to alteration.
II
HREE
z LREE
ZREE
La Ce Pr Nd Sm Eu Gel Tb Dy Ho Er Tm Yb Lu
0.73
55.16
1.5 5.9 0.65 9.4 5.0 1.8 6.2 1.23 7.8 2.0 7.0 0.68 5.2 0.80
glass (g)
DH-01
0.75
49.20
1.7 6.1 0.70 7.2 4.6 1.7 5.8 0.90 7.0 1.7 6.0 0.60 4.5 0.70
core (c)
Rare-earth elements in the basalt samples
TABLE
1.14
57.87
27.65 1.04
2.9 7.8 1.4 12 5.7 2.0 6.5 1.04 7.4 1.5 5.0 0.55 3.6 0.48
glass(g)
1.6 3.5 0.60 5.6 2.4 0.75 3.0 0.50 4.0 0.75 2.5 0.30 1.9 0.25
margin (m)
DH-12
1.11
49.65
2.2 7.5 1.2 10 4.4 1.6 5.4 0.90 6.1 1.4 4.8 0.48 3.3 0.37
core (c)
1.60
35.88
2.5 6.8 1.2 8.0 3.0 0.94 3.1 0.56 3.5 0.73 2.7 0.35 2.2 0.30
margin (m)
1.05
41.11
2.3 6.0 0.83 7.2 4.1 1.3 4.5 0.82 5.7 1.2 3.2 0.41 3.0 0.55
core (c)
DH-08
1.00
34.24
1.4 5.7 0.72 5.8 3.0 0.95 3.7 0.64 5.3 1.0 2.8 0.33 2.4 0.50
margin (m)
1.704
3.953
0.378 0.976 0.136 0.716 0.230 0.0866 0.311 0.0589 0.390 0.0888 0.255 0.0385 0.249 0~0387
Leedey chondrite
b~ i=~
272
30
>-1.1..I ','
._1
i,i
30
l
l
l
l
,
,
l
J
l
l
,
,
l
l
,
i
l
,
l ~
l 1
l 1
l 1
l 1
l
"
1
2O
rY
z
0 -i-
10
5
DH-12
._.J i
(3..
L
~
,
l
l
J
,
l
J
L
J
l
2O
,5
DH-08 I LQ
I
I
I
I
i
I
C,e Pr N(I (Pro} Sm Eu
i
I
Gd
Tb
/
i
I
I
I
I)y 140 Ef Tm Yb
I Lu
Fig. 3. Norma]ized REE plots for the pillow basalts from the Gulf of California.
The two glass samples as well as crystalline pillow interiors (cores) analyzed in this study show slight REE depletion typical of mid-ocean ridge basalts (MORB). This is consistent with the conclusion of Schilling and Bonatti (1975) that there are no significant differences between REE abundances of ridge and seamount volcanism. Instead of using La/Yb ratios, we may express, following Nance and Taylor {1976), the ratio of light to heavy REE as ~ L R E E / ~ H R E E where ZLREE is the sum of the abundances of La--Sm and Z HREE is the sum of the abundances of Gd--Lu. Such ratios for the Gulf samples (including altered margins) are all less than that for the Leedey chondrite (Table II), implying LREE depleted nature of basalts from the Gulf of California. However, the abundances of REE, especially HREE, are consistently lower in the margin than in the core o f the pillows. The Z REE (the sum of the abundances of La--Lu) is considerably less in the margin than in the core (Table II). Based on the REE patterns and ~; REE, the margins of DH-01 and DH-12 are considerably more altered than their cores. On the other hand, perhaps DH-08 is the most weathered sample
273 TABLE HI Low-temperature alteration of oceanic basalts Study Nicholls (1963) Engel et al. (1965) Miyashiro et al. (1969) Philpottset al. (1969) S.R. Hart (1969) R.A. Hart (1970) S.R. Hart and Nalwalk (1970) Christensen et al. (1973) Melson (1973) Thompson (1973) Shido et al. (1974) S.R. Hart et al. (1974) Scott and Hajash(1976) Fodor et al. (1977) Robinson et al. (1977 ) This study
Increase in basalt Fe3+/Fe2+, H20 Mn, Ti, Fe, P, H20, K K
Decrease in basalt
Constant or minor change
Ca, Mg, Na Mg, total Fe
Inconsistent trend
Na, K, Si
Si, Mg, Ca REE
K K, Fe, Ti, P, Mn, Na H20 , Fe 3÷
Si, Ca, M g
Fe 3÷, K, H20
Ca, Mg, Si
K, Fe, Ti
Ca, Mg, Na, Mn, P Ca, Mg, Si
H~O, K, Fe 3+, P, L R E E K, Fe 3÷, Ti, P, H~O Fe 3÷, total Fe, Mn, K, H20
K K, Cr H20 , K, usually CO 2, Fe3÷/Fe 2+ Fe s+, H20, K, CO2, Na
Al
Ca, Si Cr, H R E E
Fe
Ca, Si
Si, Al, Ca
Ti, Cr
total Fe H20
Mg
Mg, Na, P
A1, Ti, P Mg, Fe 2+, Mg/Fe, R E E
Cr
Si, Al, Ti, P, Mn, Ca, total Fe
as it is also starting t o lose H R E E f r o m t h e crystalline i n t e r i o r (Fig. 3). T h e p r e s e n t s t u d y shows a loss o f H R E E f r o m basalt samples during seaf l o o r weathering. This e f f e c t if c o n f i r m e d b y m o r e analyses o f s u b m a r i n e basalts f r o m this as well as o t h e r areas, should have i m p o r t a n t bearing o n t h e R E E c o n t e n t s o f seawater and o n r e l a t e d processes. ACKNOWLEDGEMENTS T h e IPOD s t a f f is t h a n k e d f o r t h e samples used in this work. We are particularly grateful t o G.D. Nicholls f o r providing t h e A E I MS7 mass
274
spectrometer and other facilities necessary for trace-element measurements. E. Camarillo helped in atomic absorption analyses. We are also much obliged to the reviewers of the journal whose comments helped us considersably to improve the presentation of our results. N. Figueroa is thanked for typing the manuscript. REFERENCES Christensen, N.I., Frey, F., MacDougall, D., Melson, W.G., Peterson, M.N.A., Thompson, G. and Watkins, N., 1973. Deep Sea Drilling Project: properties of igneous and metamorphic rocks of the oceanic crust. EOS (Am. Geophys. Union Trans.), 54: 972--981. Condie, K.C., 1976. Trace-element geochemistry of Archean greenstone belts. Earth-Sci. Rev., 12: 393--417. Engel, C.G., Fischer, R.L. and Engel, A.E.J., 1965. Igneous rocks of the Indian Ocean floor. Science, 150: 605--610. Fodor, R.V., Husler, J.W. and Keil, K., 1977. Petrology of basalt recovered during DSDP Leg 39 B. In: P.R. Supko, K. Perch-Nielsen et al., Initial Reports of the Deep Sea Drilling Project, U.S. Government Printing Office, Washington, D.C., 39: 513--523. Frey, F.A., Haskin, M.A., Poetz, J.A. and Haskin, L.A., 1968. Rare earth abundances in some basic rocks. J. Geophys. Res., 73: 6085--6098. Hart, R.A., 1970. Chemical exchange between sea water and deep ocean basalts. Earth Planet. Sci. Lett., 9: 269--279. Hart, S.R., 1969. K, Rb, Cs contents and K/Rb, K/Cs ratios of fresh and altered submarine basalts. Earth Planet. Sci. Lett., 6: 295--303. Hart, S.R. and Nalwalk, A.J., 1970. K, Rb, Cs, and Sr relationships in submarine basalts from the Puerto Rico trench. Geochim. Cosmochim. Acta, 34: 145--155. Hart, S.R., Erlank, A.J. and Kable, E.J.D., 1974. Sea floor basalt alteration: some chemical and Sr isotopic effects. Contrib. Mineral. Petrol., 44: 219--230. LSpez M., M., P~rez R., J., Urrutia F., J., Pal, S. and Terrell, D.J., 1978. Geochemistry and petrology of some volcanic rocks dredged from the Gulf of California. Geochem. J., 12: 127--132. MacDonald, G.A. and Katsura, T., 1964. Chemical composition of Hawaiian lavas. J. Petrol., 5: 82--133. Masuda, A., 1975. Abundances of monoisotopic REE, consistent with the Leedey chondrite values. Geochem. J., 9: 183--184. Masuda, A., Nakamura, N. and Tanaka, N., 1973. Fine structures of mutually normalized rare-earth patterns of chondrites. Geochim. Cosmochim. Acta, 37 : 239--248. Melson, W.G., 1973. Basaltic glasses from the Deep Sea Drilling Project -- Chemical characteristics, compositions of alteration products, and fission track "ages". EOS (Am. Geophys. Union Trans.), 54: 1011--1014. Miyashiro, A.F., Shido, F. and Ewing, M., 1969. Diversity and origin of abyssal tholeiite from the Mid-Atlantic Ridge near 24 ° and 30 ° north latitude. Contrib. Mineral. Petrol., 23: 38~52. Nance, W:~. and Taylor, S.R., 1976. Rare earth element pattern and crustal evolution, I. Australian Post-Archean sedimentary rocks. Geochim. Cosmochim. Acta, 40: 1 5 3 9 1551. Nicholls, G.D., 1963. Environmental studies in sedimentary geochemistry. Sci. Progr., 51 : 12--31. Nicholls, G.D., Graham, A.L., Williams, E. and Wood, M., 1967. Precision and accuracy in trace element analysis of geological materials using solid source spark mass spectrometry. Anal. Chem,, 39: 584--590. Philpotts, J.A., Schnetzler, C.C. and Hart, S.R., 1969. Submarine basalts: some K, Rb, St, Ba, rare-earth, H20 and CO~ data bearing on their alteration, modification by plagioclase and possible source materials. Earth Planet. Sci. Lett., 7: 293--299.
275 Robinson, P.T., Flower, M.F.J., Schminke, H.-U. and Ohnmacht, W., 1977. Low temperature alteration of oceanic basalts, DSDP Leg 37. In: F. Aumento, W.G. Melson, et al., Initial Reports of the Deep Sea Drilling Project, U.S. Government Printing Office, Washington, D.C., 37: 775--794. Schilling, J.G. and Bonatti, E. 1975. East Pacific Ridge (2°S--19°S) versus Nazca plate volcanism -- Rare-earth evidence. Earth Planet. Sci. Lett., 25: 93--102. Scott, R,B. and Hajash, Jr., A., 1976. Initial submarine alteration of basaltic pillow lavas: a microprobe study. Am. J. Sci., 276: 480--501. Shapiro, L. and Brannock, W.W., 1962. Rapid analysis of silicate, carbonate and phosphate rocks. U.S. Geol. Surv., Bull., 1144-A: 1--56. Shido, F., Miyashiro, A.F. and Ewing, M., 1974. Compositional variations in pillow lavas from the Mid Atlantic Ridge. Mar. Geol., 16: 177--190. Thompson, G., 1973. A geochemical study of the low-temperature interaction of seawater and oceanic igneous rocks. EOS (Am. Geophys. Union Trans.), 54: 1015--1019.
267
RARE-EARTH ELEMENTS IN BASALT SAMPLES, G U L F OF CALIFORNIA
D A V I D J. T E R R E L L , S U R E N D R A
PAL, M A R G A R I T A
L O P E Z M. and JOSE PI~REZ R.
Instituto de Geoffsica, Universidad Nacional Aut6noma de M$xico, M~xico 20, D.F.
(M~xico) (Received July 10, 1978; revised and accepted February 6, 1979)
ABSTRACT Terrell,D.J.,Pal, S., L6pez M., M. and P~rez R., J., 1979. Rare-earth etements in basalt samples, Gulf of California.Chem. Geol., 26: 267--275.
Results are given o f chemical analyses and rare-earth e l e m e n t s o f glass rims, crystalline interior (core) and altered exterior (margin) of three pillow basalts from the mouth of the Gulf of California. A notable alteration effect of low-temperature weathering s e e m s to he a loss of rare-earth e l e m e n t s f r o m basalt.
INTRODUCTION After an initial geochemical and petrographic study of three samples dredged from the m o u t h of the Gulf of California (LSpez M. et al., 1978), it was t h o u g h t to be o f some importance to investigate low-temperature alteration effects (halmyrolysis) on the chemistry of these samples. The rock fragments showed obvious macroscopic zoned color differences related to weathering (Fig.l); these different zones were sampled and analyzed for major elements, H20, COs and rare-earth elements (REE). Thus following S.R. Hart et al. {1974), the samples were split into three fractions: glass sampled from the surface of some pillow fragments, core sampled from a "fresh appearing" interior part of pillow fragments, and margin from presumably weathered brownish or grayish outer zone o f the fragments. The pillow fragments left from DH-08 (Fig.l) after the earlier study by LSpez M. et al. (1978) contained no glass. Thin glassy rims were present in some fragments from this site but were used up in the previous study by LSpez M. et al. (1978). ANALYTICAL METHODS For major-element chemistry a combination of classical and instrumental methods was used. Thus SiO2 and H20- were determined by gravimetry;
268
Fig.1. Basalt fragments from DH-08 showing zoned color differences. COs by the method of Shapiro and Brannock (1962); H20 ÷ by difference in loss on ignition (LOI) and CO2; A1203, total Fe (as Fe203), MnO, MgO and CaO by atomic absorption spectrometry; Na20 and K20 by flame p h o t o m e t r y ; TiO2 and P2Os by colorimetry and finally FeO (ferrous iron) by volumetry. Precisions and accuracies range between 1 and 5%. REE were measured by spark source mass spectrometry following the method of Nicholls et al. (1967). Precisions and accuracies for REE vary between 10 and 30%. RESULTS AND DISCUSSION The locations of the analyzed samples have been given by L6pez M. et al. (1978). Sample DH-01 is from the eastern flank of East Pacific rise crest, DH-12 from the southern flank of a seamount and DH-08 is from the first major slope of continental borderland. Their major-element chemistry is given in Table I. Abundances of some major elements are plotted in Fig.2. The REE contents of these samples are presented in Table II and plotted in Fig.3. The chondrite values for normalization are those for the Leedey chondrite (Masuda et al., 1973; Masuda, 1975). Presumably the quenched glass best represents the liquid composition at the time of eruption and can be used to classify the samples. Both DH-01 and and DH-12 can be classified as tholeiitic basalts as both of them fall in the tholeiitic field of Na20+K20 vs. SiO2 diagram of MacDonald and Katsura (1964). As stated earlier, no glass could be analyzed for DH-08. However,
0.40
0.41
F e O T = total iron as FeO.
FeO T + MEO
11.02
10.87
Total Fe as Fe~O3
100.01
99.82
Total
49.61 1.38 15.90 3.68 6.60 6.63 12.12 0.21 2.08 0.28 0.12 0.07 0.47 0.75 0.11
50.10 1.34 15.58 3.04 7.04 6.81 11.95 0.18 2.28 0.31 0.12 0.07 0.30 0.60 0.10
SiO~ TiO 2 A1203 Fe20 , FeO MgO CaO MnO Na20 K20 P20~ Cr203 H~O" H20 ÷ CO 2
0.38
11.31
100.04
49.39 1.31 15.74 4.77 5.88 6.16 11.85 0.38 2.19 0.37 0.12 0.07 0.67 0.97 0.17
0.46
10.08
99.06
48.47 1.63 16.83 2.28 6.80 7.70 10.52 0.21 2.80 0.35 0.17 0.06 0.38 0.76 0.10
glass (g)
margin (m)
glass Og)
core (e)
DH-12
DH-01
Major-element chemistry of the basalt samples
TABLE I
0.46
9.81
99.60
49.66 1.33 15.52 2.42 7.24 7.52 12.07 0.17 2.23 0.26 0.12 0.07 0.24 0.65 0.10
core (c)
0.35
9.32
100.06
48.85 1.78 17.77 4.81 3.51 4.56 11.82 0.12 3.10 0.34 0.17 0.06 1.31 1.66 0.20
margin (m)
0.43
10.85
99.45
48.88 1.69 15.60 2.50 7.50 7.38 11.97 0.17 2.17 0.27 0.16 0.06 0.16 0.84 0.10
core (c)
DH-08
0.40
11.57
99.95
48.94 1.66 15.54 3.42 7.32 7.08 11.94 0.16 2.24 0.33 0.16 0.06 0.27 0.70 0.13
margin (m)
t~ O~ ¢.P
270 50
4O /
40
CN ,.2
3D
/
/
I
,
o
o~
30
o
20
?
s
/
iI
I0
20
/ I ~"
o
!
o
I0
I
8O
o
~.
I
04
~'--A
o
~\
60
%
40
~
0.3
o
02i
-.f
OI
20
0
i
L
DH-OI
'
'
DH-12
'
'
DH-08
I
DH-OI
I
I
DH-12
,
DH-08
Fig.2. Behavior of some major elements during sea-floor weathering of pillow basalts (g, c a n d m stand for glass, core and margin, respectively).
both the core and the margin samples from DH-08 fall well within the tholeiitic field of Na20+K20 vs. SiO2 plot. Our results on the effects of low-temperature alteration of oceanic basalts are summarized and compared or contrasted with the findings of other workers in Table III. Thus based on major-element analyses, the rocks from the Gulf of California show an increase in Fe 3+, H2 O, CO2 and K upon alteration, a decrease in Mg and Fe 2+ and a practically constant content of Cr. As can be seen from Table III these observations are consistent with the results of most workers. A point worth noting is rather similar H20 contents of the core and the margin for DH-08. This implies that either H20 is not a good indicator of alteration or the interior of DH-08 is also considerably altered. The second possibility is supported by REE data. The most important result of the present study seems to be a loss in REE contents of basalt following alteration. This observation seems to disagree with other workers. Thus Frey et al. (1968) found that REE abundances in altered basalts are not distinctly different from those in fresh basalts and concluded that REE are not affected by the initial alteration effects caused by seawater. Philpotts et al. (1969) showed that REE apparently remain constant upon alteration. Christensen et al. (1973} have concluded that heavy REE (HREE) are least affected by halmyrolysis. However, Thompson (1973) has shown that REE, particulm'!y the light REE (LREE), increase in the altered interiors. Condie (1976) based his work on the observation that the REE are among the trace elements that are most resistant to alteration.
II
HREE
z LREE
ZREE
La Ce Pr Nd Sm Eu Gel Tb Dy Ho Er Tm Yb Lu
0.73
55.16
1.5 5.9 0.65 9.4 5.0 1.8 6.2 1.23 7.8 2.0 7.0 0.68 5.2 0.80
glass (g)
DH-01
0.75
49.20
1.7 6.1 0.70 7.2 4.6 1.7 5.8 0.90 7.0 1.7 6.0 0.60 4.5 0.70
core (c)
Rare-earth elements in the basalt samples
TABLE
1.14
57.87
27.65 1.04
2.9 7.8 1.4 12 5.7 2.0 6.5 1.04 7.4 1.5 5.0 0.55 3.6 0.48
glass(g)
1.6 3.5 0.60 5.6 2.4 0.75 3.0 0.50 4.0 0.75 2.5 0.30 1.9 0.25
margin (m)
DH-12
1.11
49.65
2.2 7.5 1.2 10 4.4 1.6 5.4 0.90 6.1 1.4 4.8 0.48 3.3 0.37
core (c)
1.60
35.88
2.5 6.8 1.2 8.0 3.0 0.94 3.1 0.56 3.5 0.73 2.7 0.35 2.2 0.30
margin (m)
1.05
41.11
2.3 6.0 0.83 7.2 4.1 1.3 4.5 0.82 5.7 1.2 3.2 0.41 3.0 0.55
core (c)
DH-08
1.00
34.24
1.4 5.7 0.72 5.8 3.0 0.95 3.7 0.64 5.3 1.0 2.8 0.33 2.4 0.50
margin (m)
1.704
3.953
0.378 0.976 0.136 0.716 0.230 0.0866 0.311 0.0589 0.390 0.0888 0.255 0.0385 0.249 0~0387
Leedey chondrite
b~ i=~
272
30
>-1.1..I ','
._1
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30
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l
l
,
,
l
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._.J i
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Fig. 3. Norma]ized REE plots for the pillow basalts from the Gulf of California.
The two glass samples as well as crystalline pillow interiors (cores) analyzed in this study show slight REE depletion typical of mid-ocean ridge basalts (MORB). This is consistent with the conclusion of Schilling and Bonatti (1975) that there are no significant differences between REE abundances of ridge and seamount volcanism. Instead of using La/Yb ratios, we may express, following Nance and Taylor {1976), the ratio of light to heavy REE as ~ L R E E / ~ H R E E where ZLREE is the sum of the abundances of La--Sm and Z HREE is the sum of the abundances of Gd--Lu. Such ratios for the Gulf samples (including altered margins) are all less than that for the Leedey chondrite (Table II), implying LREE depleted nature of basalts from the Gulf of California. However, the abundances of REE, especially HREE, are consistently lower in the margin than in the core o f the pillows. The Z REE (the sum of the abundances of La--Lu) is considerably less in the margin than in the core (Table II). Based on the REE patterns and ~; REE, the margins of DH-01 and DH-12 are considerably more altered than their cores. On the other hand, perhaps DH-08 is the most weathered sample
273 TABLE HI Low-temperature alteration of oceanic basalts Study Nicholls (1963) Engel et al. (1965) Miyashiro et al. (1969) Philpottset al. (1969) S.R. Hart (1969) R.A. Hart (1970) S.R. Hart and Nalwalk (1970) Christensen et al. (1973) Melson (1973) Thompson (1973) Shido et al. (1974) S.R. Hart et al. (1974) Scott and Hajash(1976) Fodor et al. (1977) Robinson et al. (1977 ) This study
Increase in basalt Fe3+/Fe2+, H20 Mn, Ti, Fe, P, H20, K K
Decrease in basalt
Constant or minor change
Ca, Mg, Na Mg, total Fe
Inconsistent trend
Na, K, Si
Si, Mg, Ca REE
K K, Fe, Ti, P, Mn, Na H20 , Fe 3÷
Si, Ca, M g
Fe 3÷, K, H20
Ca, Mg, Si
K, Fe, Ti
Ca, Mg, Na, Mn, P Ca, Mg, Si
H~O, K, Fe 3+, P, L R E E K, Fe 3÷, Ti, P, H~O Fe 3÷, total Fe, Mn, K, H20
K K, Cr H20 , K, usually CO 2, Fe3÷/Fe 2+ Fe s+, H20, K, CO2, Na
Al
Ca, Si Cr, H R E E
Fe
Ca, Si
Si, Al, Ca
Ti, Cr
total Fe H20
Mg
Mg, Na, P
A1, Ti, P Mg, Fe 2+, Mg/Fe, R E E
Cr
Si, Al, Ti, P, Mn, Ca, total Fe
as it is also starting t o lose H R E E f r o m t h e crystalline i n t e r i o r (Fig. 3). T h e p r e s e n t s t u d y shows a loss o f H R E E f r o m basalt samples during seaf l o o r weathering. This e f f e c t if c o n f i r m e d b y m o r e analyses o f s u b m a r i n e basalts f r o m this as well as o t h e r areas, should have i m p o r t a n t bearing o n t h e R E E c o n t e n t s o f seawater and o n r e l a t e d processes. ACKNOWLEDGEMENTS T h e IPOD s t a f f is t h a n k e d f o r t h e samples used in this work. We are particularly grateful t o G.D. Nicholls f o r providing t h e A E I MS7 mass
274
spectrometer and other facilities necessary for trace-element measurements. E. Camarillo helped in atomic absorption analyses. We are also much obliged to the reviewers of the journal whose comments helped us considersably to improve the presentation of our results. N. Figueroa is thanked for typing the manuscript. REFERENCES Christensen, N.I., Frey, F., MacDougall, D., Melson, W.G., Peterson, M.N.A., Thompson, G. and Watkins, N., 1973. Deep Sea Drilling Project: properties of igneous and metamorphic rocks of the oceanic crust. EOS (Am. Geophys. Union Trans.), 54: 972--981. Condie, K.C., 1976. Trace-element geochemistry of Archean greenstone belts. Earth-Sci. Rev., 12: 393--417. Engel, C.G., Fischer, R.L. and Engel, A.E.J., 1965. Igneous rocks of the Indian Ocean floor. Science, 150: 605--610. Fodor, R.V., Husler, J.W. and Keil, K., 1977. Petrology of basalt recovered during DSDP Leg 39 B. In: P.R. Supko, K. Perch-Nielsen et al., Initial Reports of the Deep Sea Drilling Project, U.S. Government Printing Office, Washington, D.C., 39: 513--523. Frey, F.A., Haskin, M.A., Poetz, J.A. and Haskin, L.A., 1968. Rare earth abundances in some basic rocks. J. Geophys. Res., 73: 6085--6098. Hart, R.A., 1970. Chemical exchange between sea water and deep ocean basalts. Earth Planet. Sci. Lett., 9: 269--279. Hart, S.R., 1969. K, Rb, Cs contents and K/Rb, K/Cs ratios of fresh and altered submarine basalts. Earth Planet. Sci. Lett., 6: 295--303. Hart, S.R. and Nalwalk, A.J., 1970. K, Rb, Cs, and Sr relationships in submarine basalts from the Puerto Rico trench. Geochim. Cosmochim. Acta, 34: 145--155. Hart, S.R., Erlank, A.J. and Kable, E.J.D., 1974. Sea floor basalt alteration: some chemical and Sr isotopic effects. Contrib. Mineral. Petrol., 44: 219--230. LSpez M., M., P~rez R., J., Urrutia F., J., Pal, S. and Terrell, D.J., 1978. Geochemistry and petrology of some volcanic rocks dredged from the Gulf of California. Geochem. J., 12: 127--132. MacDonald, G.A. and Katsura, T., 1964. Chemical composition of Hawaiian lavas. J. Petrol., 5: 82--133. Masuda, A., 1975. Abundances of monoisotopic REE, consistent with the Leedey chondrite values. Geochem. J., 9: 183--184. Masuda, A., Nakamura, N. and Tanaka, N., 1973. Fine structures of mutually normalized rare-earth patterns of chondrites. Geochim. Cosmochim. Acta, 37 : 239--248. Melson, W.G., 1973. Basaltic glasses from the Deep Sea Drilling Project -- Chemical characteristics, compositions of alteration products, and fission track "ages". EOS (Am. Geophys. Union Trans.), 54: 1011--1014. Miyashiro, A.F., Shido, F. and Ewing, M., 1969. Diversity and origin of abyssal tholeiite from the Mid-Atlantic Ridge near 24 ° and 30 ° north latitude. Contrib. Mineral. Petrol., 23: 38~52. Nance, W:~. and Taylor, S.R., 1976. Rare earth element pattern and crustal evolution, I. Australian Post-Archean sedimentary rocks. Geochim. Cosmochim. Acta, 40: 1 5 3 9 1551. Nicholls, G.D., 1963. Environmental studies in sedimentary geochemistry. Sci. Progr., 51 : 12--31. Nicholls, G.D., Graham, A.L., Williams, E. and Wood, M., 1967. Precision and accuracy in trace element analysis of geological materials using solid source spark mass spectrometry. Anal. Chem,, 39: 584--590. Philpotts, J.A., Schnetzler, C.C. and Hart, S.R., 1969. Submarine basalts: some K, Rb, St, Ba, rare-earth, H20 and CO~ data bearing on their alteration, modification by plagioclase and possible source materials. Earth Planet. Sci. Lett., 7: 293--299.
275 Robinson, P.T., Flower, M.F.J., Schminke, H.-U. and Ohnmacht, W., 1977. Low temperature alteration of oceanic basalts, DSDP Leg 37. In: F. Aumento, W.G. Melson, et al., Initial Reports of the Deep Sea Drilling Project, U.S. Government Printing Office, Washington, D.C., 37: 775--794. Schilling, J.G. and Bonatti, E. 1975. East Pacific Ridge (2°S--19°S) versus Nazca plate volcanism -- Rare-earth evidence. Earth Planet. Sci. Lett., 25: 93--102. Scott, R,B. and Hajash, Jr., A., 1976. Initial submarine alteration of basaltic pillow lavas: a microprobe study. Am. J. Sci., 276: 480--501. Shapiro, L. and Brannock, W.W., 1962. Rapid analysis of silicate, carbonate and phosphate rocks. U.S. Geol. Surv., Bull., 1144-A: 1--56. Shido, F., Miyashiro, A.F. and Ewing, M., 1974. Compositional variations in pillow lavas from the Mid Atlantic Ridge. Mar. Geol., 16: 177--190. Thompson, G., 1973. A geochemical study of the low-temperature interaction of seawater and oceanic igneous rocks. EOS (Am. Geophys. Union Trans.), 54: 1015--1019.