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Origin of clay minerals in a Mid-Atlantic Ridge sediment
EARTH AND PLANETARY SCIENCE LETTERS 10 (1971) 186-192. NORTH-HOLLANDPUBLISHINGCOMPANY
ORIGIN OF CLAY MINERALS IN A MID-ATLANTIC RIDGE SEDIMENT R.A. COPELAND*, F.A. FREY and D.R. WONES Department o f Earth and Planetary Sciences, Massachusetts Institute o f Technology, Cambridge, Massachusetts 02139, USA
Received 19 July 1970 Revised version received 10 November 1970
The coarse and fine-grained mineral fractions of a Mid-Atlantic Ridge sediment (22°N) have been separated and analyzed for Fe and rare-earth elements (REE). Despite changes in Fe abundance, all the chlorites have REE distributions consistent with a derivation from ridge greenstones. The REE distribution of the fine-grained monlrnorillonite is similar to that of shales, yet differs markedly from that of a coarse 16eally derived iron-riehmontmorillonite. A continental origin for the fine-grained montmorillonite is implied.
1. Introduction The problem of provenance, especially for finegrained marine sediments, has undergone intensive investigation [ 1 - 4 ] . Biscaye [ 1] has shown that the majority of the noncarbonate fine fraction in the Atlantic Ocean is of continental origin. Local origins have been reported for some coarse fractions of MidAtlantic Ridge sediments [3,4]. The amount of local contribution to the finer fraction often remains in doubt. Siever and Kastner [3] suggested a local origin for some of the finer sediment in ponds of the MidAtlantic Ridge. Their conclusion was based on optical and X-ray diffraction studies of texture and crystallinity. Trace element analysis of the sediment and the proposed nearby source rocks might demonstrate whether or not part of the finer portion is of local ori. gin. The postulated local source rocks for the MidAtlantic Ridge sediments are ridge basalts (oceanic tholeiites) and associated metamorphic rocks (greenstones). The greenstones have been interpreted as a metamorphic product of tholeiitic basalts [5,6]. Frey et al. [7] observed that the rare earth element (REE) distributions of the basalts are not radically * Now at Great Lakes Research Division, University of Michigan, Ann Arbor, Michigan.
changed during the postulated metamorphism to greenstones. The REE distributions of these basalts and greenstones are depleted in light REE relative to the distributions observed in oceanic sediments [8] and in most continental rocks [9]. If the sedimentary minerals derived from the MidAtlantic Ridge basalts and greenstones retain a light REE depletion, then REE analyses of the sediment minerals would identify the locally derived minerals. We have analyzed the constituent phases of two surface dredge samples studied by Siever and Kastner
[3]. 2. Sample description The Chain 44 Dredge 3 sample is from the median valley region at 22°38.01'N from 45°0.7 to 44°58.8'W at a depth of 2400-3400 m. This sample was chosen for two reasons: (1) the coarse-fraction contains mineral and rock fragments of local origin; (2) the presence of well-crystallized montmoriUonite. The THV 15 sediment was collected in the median valley at 22°47.5 from 45 ° 11.4 to 45 ° 12.2'W at a depth of 2460-2630 m. It is an unusual sample, consisting primarily of amorphous material in the less than 10ta fraction.
R.A. Copeland et al., Origin of clay minerals 3. E x p e r i m e n t a l
187
data, one c o n t a i n e d a b o u t 80% chlorite, 10% kaolinite and 10% illite and the o t h e r a b o u t 65% m o n t m o r i l l o n ite, 20% chlorite, 10% illite and 5% kaolinite. Since the T H V 15 sample was primarily amorphous, electrophoresis separation was impossible. A less than 10/z fraction was separated, equilibrated 10 min w i t h 25% v/v acetic acid, washed and analyzed w i t h o u t further t r e a t m e n t . All samples were analyzed for Fe and R E E b y instrumental n e u t r o n activation analysis [ 12]. Small sample size (1 or 2 mg) and interference f r o m o t h e r elements limited our R E E analyses to data for La, Ce, Eu, Dy and Lu. The values r e p o r t e d in table 1 are believed accurate within the error limits given. Error limits were based on c o u n t i n g statistics, reproducibility and interferences. C o n c u r r e n t analysis o f W-1 and G-1 gave results within the range o f previously observed values for
The C h 4 4 sample was separated i n t o a greater than 63/~ and a 1 - 1 0 / a fraction b y sieving and centrifuging. E a c h fraction was t h o r o u g h l y washed w i t h distilled d e i o n i z e d water. Samples o f unaltered glass, chlorites, and a yellow-orange m o n t m o r i l l o n i t e ( n o n t r o n i t e ) were picked f r o m the coarse fraction. In addition, a greenstone f r a g m e n t f r o m the same dredge was crushed and the chlorite was separated. The 1-10bt fraction was equilibrated for 10 min. w i t h 25% v/v acetic acid to r e m o v e calcium carbonate and m e t a l h y d r a t e s and t h e n b u f f e r e d in 2 X 10-4M sodium carbonate. Such an acid t r e a t m e n t does n o t appreciably dissolve the clay minerals [ 1 0 ] . The clay minerals were separated b y c o n t i n u o u s particle electrophoresis [11 ]. T w o principal fractions (1 mg) were collected for analysis. O n the basis o f X-ray diffraction
Table ! Fe (%) and REE (ppm) abundances. Sample Ch44Dr3: Chlorite from greenstone Iron-richchloritea(>63/~) Magnesium-richchloriteb(>63/a) 1-10/achlorite c Palagonite Nontronite 1-10~tMontmoriUonite d THV15: Amorphous ( < 10/~) Continental clays: Belle Fourche montmorillonite f Mainemontmorillonite Metamorphic chlorites: Swedish chlorite Ural Mountains chlorite Standard rocks: G-1 (granite) G-1 literature g W-1 (diabase) W-1 literature g a
Fe
13.8+0.6 10.0-+0.5 8.8-+0.4 5.4+0.4 10.2 +- 0.6 24.2 +- 1.5 14.4-+0.9
La
5.2 3.2 4.7 3.0
C¢
Eu
Dy
-+ 0.7 +-0.7 -+ 0.7 -+ 0.3 5 -+ 1 3 -+ 1 43-+6
_e 18 -+ 6 92-+10
1.2 1.7 1.6 1.2 1.9 2.2 3.1
-+0.2 -+0.2 -+0.2 -+0.4 -+ 0.2 -+ 0.3 -+0.6
4-+1 5-+1 4-+1 7 -+ 2 9 -+ 2 8-+3
0.45 0.45 0.54 0.7 0.65 1.1 1.3
-
43 -+ 3
52 -+ 10
1.6 -+0.2
6 -+ 1
0.46 -+0.06
-
65 -+4 5.5 -+ 0.7
130 -+ 20
0.75 -+ 0.12
8 -+ 1
0.48 -+ 0.06
-
0.5
-
0.39 -+ 0.06 0.11 -+ 0.05
-
1.6 -+0.2 1.35 6.9-+0.7 7.71
123-+6 85 --110 14-+3 9.31 - 13.5
-
-+0.1
+0.04 -+0.07 -+0.05 -+0.2 -+ 0.08 -+0.2 -+0.3
-
0.3
0.06 -+0.03 0.15 -+ 0.008
-
0.05 -+0.02 0.010 -+0.005
1.6 -+0.3 1.04 - 1.36 1-+0.1 0.95 --1.29
-
0.18 0.12 0.32 0.325
Sample includes 10-20% actinolite. Some Mg-rich chlorite surrounds an inner core of Fe-rich chlorite. c Contains 20% illite and kaolinite. d Contains 15% illite and kaolinite. All values have been corrected for a 20% 1-10~ chlorite contamination. e ( - ) indicates not determined. f Tb + 1.7 _+0.4, y b = 3 + 1. g Fe data from [ 2 3 ] . Ranges of REE data from [ 2 4 ] . b
Lu
-+0.1
-+0.02 - 0.17 -+0.03 - 0.353
188
R.A. Copeland et al. Origin o f clay minerals
W-l, but our data for G-1 are systematically too high by 10-20% (table 1). The reasons for this discrepancy are unknown. A possible systematic error will not affect the following discussion which is based only on relative abundances.
4. Chlorites The likely sources of the coarse-grained chlorites in Ch44 Dr3 are the ridge greenstones [3]. Microprobe analyses of chlorites in ridge greenstones indicate about equal amounts of FeO and MgO (~ 20%) [5]. Our Fe results for a chlorite separated from a Ch44 Dr3 greenstone indicate a similar Fe abundance (18% FeO, table 1). Ch44 Dr3 chlorites have varying Fe/Mg ratios. Seiver and Kastner [3] proposed an alteration sequence from fresh dark-green chlorites (Fe-rich) to brownish-green chlorites (Mg-rich). Our optical examination indicated that green iron-rich chlorites were sometimes mantled by brown-green magnesium-rich chlorite. Fig. 1 outlines a possible alteration sequence. Iron abundances decrease in this proposed sequence (table 1). The reported iron abundances for the Ch44Dr3 chlorites are uncertain because of the impurity of the
~ PALAGONITE
BASAL~ TS
THOLEIITIC
GREENSTONES (ORIGINAL IRON-RICHCHLORITE)
i
IRON- RICH CHLORITE
YELLOW-ORANGE NONTRONITE
MAGNESIUM- RICH CHLORITE
~FINE
SEDIMENT/ ( I- IO/J.CHLORITE) ( I- IO/J. MONTMORILLONITE)
Fig. 1. Postulated alteration sequence important in deriving the clays of Ch44 Dr3 sediment.
separates mentioned in table 1. Nevertheless, the freegrained chlorite is clearly deficient in iron compared to the greenstone chlorite. This observation of iron depletion in fine-grained chlorites contrasts with the conclusions of Biscaye [1], and Griffin et al. [2]. Utilizing X-ray diffraction data, they concluded that deep sea sedimentary chlorites are consistently iron enriched. For example, Griffin et al. [2], using a semiquantitative X-ray technique, estimated that chlorites in deep-sea sediments have 2.5-4.5 heavy atoms occupying the 6 octahedral sites. This heavy atom content implies FeO contents o f > 20%. Biscaye [13] did report that chlorites from some Mid-Atlantic Ridge sediments may contain lower amounts of iron. Iron-rich chlorite may react with the marine environment either through an iron/magnesium exchange with sea water, or through oxidation-reduction changes: the latter mechanism has been observed in the reactions of synthetic micas [14]. In a simple exchange process, the chlorites should not alter except for changes in refractive indices and in intensities of 001 diffraction peaks. In an oxidation reaction, the Al/Si ratio could also change, forming a more aluminous or siliceous material depending on the initial composition. Table 2 indicates the chlorite X-ray properties, refractive indices, and chemical parameters which can be estimated from this data. The choice between mechanisms is not clear. Although variations in doo~ and refractive index are observed, the Al/Si ratio is constant within limits of error. The brownish-green chlorite appears to be a mixture (Mg-rich) of two phases. The 001 diffraction peaks are broadened compared to the green (Fe-rich) chlorite. The anomalously low refractive index is consistent with the oxidation process, but the 001 line broadening could result from either the oxidation or the exchange mechanism. The observed Fe abundance trends are confirmed by semiquantitative techniques for estimating the fraction of Fe atoms in the octahedrai sites (table 2). The method utilizing doo~ intensity ratios [I 5] has not been used for the Ch44 Dr3 coarse-grained chlorites since the assymetric correction factors (loo3/Ioo5) are unreasonable. This technique was used on a marine chlorite from a sediment far from the Mid-Atlantic Ridge (AII32, core 22, 44°44'N, 44°05'W). The cal-
R.A. Copeland et aL, Origin o f clay minerals
189
Table 2 Chlorite optical and X-ray properties.
11002
+
Fe/2: octa. sites
1004
20(060) doo1
I.R. (mean)
2AIlV 3I.R. 1Ioo1 2do6o
1oo3 corr
Ch44 Dr3 Iron-rich chlorite (>63u) 59.8 ° Mg-rich chlorite (>63u) 60.0 ° 1-10/~ chlorite 60.1 ° At111-32 Core 22 (26-33 cm) -
14.23 + 0.01 14.25 -+0.03 14.21 + 0.05
5.3 5.0 2.82
1.618 + 0.002 1.570 + 0.002 1.610
14.25 + 0.02
6.28
-
1.10-+0.03 0.42 1.09 + 0.09 1.10 +0.06 0.25 -
0.10
0.27 0.15 0.09
observ. 0.18 0.15 0.09
0.53
1. Petruk [ 15], Ioo3has not been corrected for the coarse chlorites of Ch44 Dr3. 2. Brindley [16]. 3. Albee [25]. culated fraction o f Fe atoms in octahedral sites is in the range observed by Griffin et al. [2]. The (Fe/Z octa. sites) ratios calculated from do6o [16] agree best with the observed Fe abundances. All the indirect methods demonstrate the low Fe content of the l - I 0# chlorite in the Ch44 Dr3 sample. This chlorite differs in composition from those commonly found in pelagic sediments [2]. Fig. 2 shows the REE data for the four chlorites outlined in fig. 1. The two coarse-grained chlorites which appear to be locally derived [3] have the light REE depletion characteristic of the parent greenstones. This depletion is indicated by La/Lu ratios o f 7.1 and 8.7 compared to a typical sediment value of 65 [17]. Fig. 2 also shows the REE data for the 1 - 1 0 # chlorite separated from the sediment by electrophoresis. The origin o f this fine-grained chlorite is uncertain. It has a La/Lu ratio of 4.3 which is consistent with its derivation (fig. 1) from the coarser local chlorite. All four chlorites have similar absolute REE abundances. The known impurities in some o f the chlorite separates (table 1) have not caused significant changes in the abundances. The duplication (within error limits) of REE distributions in the ridge chlorites suggests, but does not conclusively prove, a local origin for the 1 - 1 0 # chlorite. Two other possible explanations o f the similarity in REE distribution are: (1) The chlorites have REE contents in equilibria with sea water, (2) The chlorites have a characteristic crystal chemical effect o f dis. crimination against the larger REE. The expected REE content o f chlorites in equili-
ioo 80 SO 50 40
a=
• + A o
NORTH ~'% AMERICAN ~ SHALES ~
= = = =
GREENSTONE CHLORITE IRON-RICH CHLORITE MAGNESIUM-RICH CHLORITE I - I 0 / ~ CHLORITE
z
~ 3o ~ 2o br~
g
-
.
L~ I Lo
_.
.
.
GREENSTONE CH. 4 4 - 3 - 2 L Eu
L Dy
L Lu
Fig. 2. Comparison diagram for the chlorites associated with the Ch44 Dr3 sediment. Also shown are data for a Ch44 Dr3 greenstone (3-2 from ref. [7] ) and composite results for shales and ocean ridge basalts [7,9]. Chondrite values from[9]. brium with sea-water is difficult to evaluate. Seawater characteristically has La/Lu ratios of 8 to 30 [ 18]. Crystal chemical arguments for chlorite would suggest that equilibrium La/Lu ratios in chlorite should be lower than in sea-water, but the postulated high stability of heavy REE complexes [19] in sea water would tend to increase the La/Lu ratio in coexisting phases. Absolute REE abundances in the chlori. tes are l06 times those in sea water. If this reflects an equilibrium situation, much higher mineral-aqueous solution distribution coefficients must exist in sea water than those experimentally determined for the REE partitioning between silicate minerals and pure water [20]. To obtain information about possible crystal chemical discrimination against the light REE, we
190
R.A. Copeland et aL, Origin o f clay minerals
analyzed two chlorites from metamorphic rocks for REE (table 1). Both of these chlorites have lower REE abundances than the chlorites from Ch44 Dr3. However, in all six chlorites the La/Lu ratios are low (4 to 12) relative to the typical sedimentary value of 65. Although we do not have information about the phases coexisting with these metamorphic chlorites, it is clear that a crystal effect is possible. The low Fe abundances and REE data suggest that the Ch44 Dr3 fine-grained chlorites are locally derived, but our data are insufficient to prove a local origin. Fe, Mg and REE analyses of marine chlorites from non-ridge areas could provide pertinent data.
,200
i I I[ ~q'~ c.h 1001 -£1 ~ .
sol-
I
E: 7 0 J c~ 6 0 / -
T
l
~
L
zo'. (
$. f /
Lo Ce
i I o = i-lOFt MONTMORILLONITE A = THV 15 AMORPHOUS • = COARSE NONTRONITE
+ = PALAGONITE
~-
I
--
U
~
1
Eu
lIT~ - - = ,rl
Oy
z
,z-
r1
Yb Lu
5. Montmorillonite
Fig. 3. Comparison diagram for phases which may have been precursors of the fine-grained(1-10tO montmorillonite. Chondrite values from [9].
A proposed sequence for the formation of montmoriUonite is shown in fig. 1. Red to brown glass (palagonite) is common on the chilled margins of ridge tholeiitic basalts [6], and is abundant in the coarse sediment fraction of Ch44 Dr3. A coarsegrained (> 63/a) yellow-orange montmorillonite (nontronite, 24.2% Fe) is also abundant in the sediment, forming directly as an alteration product of the palagonite. It may also be related to the montmorillonite (saponite) found in the Ch44 Dr3 greenstones [6]. The transition between nontronite and 1-10/a montmoriUonite is a possibility which will be discussed. The iron content (20.6% Fe2Oa) of the fine-grained montmorillonite is higher than the range (7-15%) observed in oceanic montmoriUonites [2]. Fig. 3 shows the REE data for the palagonite, nontronite, THV15 amorphous material and the Ch44 Dr3 1-10/z montmorillonite. The light REE are relatively depleted in the palagonite and nontronite (La/Lu = 7.7 and 2.7). The 1-10# montmorillonite has a La/Lu ration of 33. This light REE enrichment is not caused by the iUite-kaolinite contamination since similar contamination levels in the fine-grained chlorite did not cause such enrichment. The absolute abundances of the REE are greater in 1-10/~ montmorillonite than in the chlorites (table 1). In the 1-10/a fraction of Ch44 Dr3 less than 30% of the sediment is montmoriUonite (estimated from X-ray diffraction data), yet more than 80% of the total REE in the 1-10/~ fraction is contained in the montmoriUonite fraction. This indicates
a greater ease of substitution of rare earths into montmorillonite than into chlorite. It is probable that the REE in montmorillonite are strongly bound in the interlayer cation positions, and will not readily exchange with sea-water. Four sources exist from which the 1-10/.t montmorillonite may have originated. First, it may be a product of the direct mechanical breakup of nontronite. Second, it may originate directly from palagonite. Third, it may crystallize from amorphous material. Finally, it may be continental in origin. If the 1-10tz montmorillonite originated from the palagonite or nontronite, considerable amounts of La and Ce must be introduced in the process. There is no obvious source for these elements. Sediments predominantly amorphous (THV 15) in the < 10# range occur near Ch44 Dr3. The origin of this amorphous material is uncertain, but it has been interpreted as an alteration product from volcanic glass and ash [3,21 ]. The THV 15 amorphous material is relatively enriched in the light REE (La/Lu = 94). In this respect it is a more suitable parent for the finegrained montmoriUonite than the nontronite or palagonite. Amorphous material is much less abundant than montmoriUonite in Mid-Atlantic Ridge sediments [3,21 ]. Thus the amorphous material is an unlikely parent unless the conversion to montmorillonite is rapid. Hydrothermal heating experiments at 250°C and 2 kbar for one week have not converted the amorphous material to montmorillonite. As a result
R.A. Copeland et al., Origin o f clay minerals
we conclude that light REE enrichment is not sufficient evidence to identify the amorphous material as a precursor to the Ch44 Dr3 fine-grained montmorillonite. Two montmorillonites from continental occurrences have also been analyzed for REE (table 1). The La/Lu ratios are quite different (18 and 135). These extreme values span the La/Lu range found in continental rocks such as granites and sediments (La/Lu = 6 0 - 8 0 , [9] ). The absolute REE abundances in the two continental montmorillonites and the Ch44 Dr3 fine-grained montmorillonite are similar to those found in shales [17]. It seems likely that montmorlllonite is the dominant host mineral for the REE in most shales and pelagic sediments [8]. Since the Ch44 Dr3 fine-grained montmorillonite has a La/Lu ratio and REE abundances within the ranges observed in continental montmoriUonites, we suggest that this material has a continental origin. The data presented demonstrate that the coarse mineral fractions o f ridge sediments have REE abundances characteristic o f their source rock. Further research is necessary, but it is also possible that the finegrained chlorite fraction retains a parent REE distribution despite changes in iron abundances. Since the REE distributions in continental detritus are quite d i f ferent from those in oceanic ridge rocks [7], the REE distributions of pelagic chlorites and montmorillonites may be a valuable indicator of provenance. Furthermore, because unique trace element abundances characterize oceanic ridge rocks [22], trace element studies of sediment phases derived from an oceanic ridge may be a useful method for studying the history of an oceanic ridge system. The sediments immediately overlying basalt in Joides cores (Legs 2 and 3) might be particularly informative.
Acknowledgement
The authors thank Drs. Vaughn T. Bowen and Geoffrey Thompson o f Woods Hole Oceanographic Institution for supplying the samples used and offering many helpful suggestions. We also thank Prof. H. Holland and Dr. James Drever who made available time and equipment at Princeton University. This research was supported by the U.S. Office of Naval Research under NR 083-157 ONR Contract Nonr.
191
1841 (74). Neutron irradiations were made at the Massachusetts Institute of Technology nuclear reactor. The samples were collected on cruises o f the Woods Hole Oceanographic Institution and the Scripps Institute of Oceanography. These cruises were supported variously by the Atomic Energy Commission, the National Science Foundation, and the Office of Naval Research.
References
[1] P.E. Biscaye, Mineralogy and sedimentation of recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans, Bull. Geol. Soc. Amar. 76 (1965) 803. [2] J.J. Griffm, H. Windom and E.D. Goldberg, The distribution of clay minerals in the world ocean, Deep Sea Res. 15 (1968) 433. [3] R. Siever and M. Kastner, Mineralogy and petrology of some Mid-Atlantic ridge sediments, J. Marine Res. 25 (1967) 263. [4] P.J. Fox and B.C. Heezen, Sands of the Mid-Atlantic Ridge, Science 149 (1965) 1367. [5] W.G. Melson and T.H. Van Andel, Metamorphism in the Mid-Atlantic Ridge, 22°N. latitude, Marine Geol. 4 (1965) 165. [6] W.G. Melson, G. Thompson and T.H. Van Andel, Vulcanism and metamorphism in the Mid-Atlantic Ridge 22°N latitude, J. Geophys. Res. 73 (1968) 5925. [7] F.A. Frey, M.A. Haskin, J.A. Poetz and L.A. Haskin, Rare earth abundances in some basic rocks, J. Geophys. Res. 73 (1968) 6085. [8] T.R. Wildeman, L.A. Haskin, Rare-earth elements in ocean sediments, J. Geophys. Res. 70 (1965) 2905. [9] L.A. Haskin, M.A. Haskin, F.A. Frey and T.R. Wilder man, Relative and absolute terrestrial abundances of the rare earths, in: Origin and Distribution of the Elements, ed. L.H. Ahrens (Pergamon, New York, 1968) p. 889. [10] R. Chester and M.J. Hughes, A chemical technique for the separation of ferromanganese minerals, carbonate minerals and absorbed trace elements from pelagic sediments, Chem. Geol. 2 (1967) 249. [ 11 ] J.I. Drever, The separation of clay minerals by continuous particle eleetrophoresis, Am. Mineralogist 54 (1969) 937. [12] G.E. Gordon, K. Randle, G. Goles, J. Corliss, M. Beeson and S. Oxley, Instrumental activation analysis of standard rocks with high resolution 3,-ray detectors, Geochim. Cosmochim. Acta 32 (1968) 369. [13] P.E. Biscaye, Distinction between kaolinite and chlorite in recent sediments by X-ray diffraction, Am. Mineralogist 49 (1964) 1281.
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R.A. Copeland et al., Origin o f clay minerals
[14] D.R. Wones and H.P. Eugster, Stability of biotite: experiment, theory and application, Am. Mineralogist 50 (1965) 1228. [ 15 ] W. Petruk, Determination of the heavy atom content in chlorite by means of the X-ray dfffractometer, Am. Mineralogist 49 (1964) 61. [16] G.W. Brindley, Chlorite minerals, in: The X-ray Identification and Crystal Structures of Clay Mineral, ed. G. Brown (London, Mineral. Society, 1961) p. 268. [17] L.A. Haskin, T.R. Wildeman, F.A. Frey, K.A. Collins, C.R. Keedy and M.A. Haskin, Rare earths in sediments, J. Geophys. Res. 71, 24 (1966b) 6091. [18] O.T. Hogdahl, S. Melson and V.T. Bowen, Neutron activation analysis of lanthanide elements in sea water, in: Trace Inorganics in Water, Advances in Chemistry Series 73, ed. R.F. Gould (Amer. Chem. Soc., Washington, D.C., 1968) p. 308. [19] E.D. Goldberg, M. Koide, R.S. Schmitt and R.H. Smith, Rare-earth distributions in the marine environment, J. Geophys. Res., 68, 14 (1962) 4201.
[20] R.L. Cullers, L.G. Medaris and L.A. Haskin, Gadolinium: Distribution between aqueous and silicate phases, Science 169 (1970) 580. [21] J.W. Murray, The clay mineralogy of marine sediments in the North Atlantic at 20°N latitude, Earth Planet. Sci Letters 10 (1970) 39. [22] A.E. Engel, C.G. Engel and R.G. Havens, Chemical characteristics of oceanic basalts and the upper mantle, Bull. Geol. Soc. Amer. 76 (1965) 719. [23] M. Fleischer, U.S. Geol. Surv. Standards-I. Additional data on rocks G-1 and W-l, 1965-1967; Geochim. Cosmochim. Acta 33 (1969) 65. [24] H. Higuchi, K. Tomura, N. Onuma and H. Hamaguchi, Rare earth abundances in several geochemical standard rocks, Geochim. J. 3 (1969) 171. [25] A.S. Albee, Relationships between the mineral association, chemical composition and physical properties of the chlorite series, Am. Mineralogist 47 (1962) 870.
ORIGIN OF CLAY MINERALS IN A MID-ATLANTIC RIDGE SEDIMENT R.A. COPELAND*, F.A. FREY and D.R. WONES Department o f Earth and Planetary Sciences, Massachusetts Institute o f Technology, Cambridge, Massachusetts 02139, USA
Received 19 July 1970 Revised version received 10 November 1970
The coarse and fine-grained mineral fractions of a Mid-Atlantic Ridge sediment (22°N) have been separated and analyzed for Fe and rare-earth elements (REE). Despite changes in Fe abundance, all the chlorites have REE distributions consistent with a derivation from ridge greenstones. The REE distribution of the fine-grained monlrnorillonite is similar to that of shales, yet differs markedly from that of a coarse 16eally derived iron-riehmontmorillonite. A continental origin for the fine-grained montmorillonite is implied.
1. Introduction The problem of provenance, especially for finegrained marine sediments, has undergone intensive investigation [ 1 - 4 ] . Biscaye [ 1] has shown that the majority of the noncarbonate fine fraction in the Atlantic Ocean is of continental origin. Local origins have been reported for some coarse fractions of MidAtlantic Ridge sediments [3,4]. The amount of local contribution to the finer fraction often remains in doubt. Siever and Kastner [3] suggested a local origin for some of the finer sediment in ponds of the MidAtlantic Ridge. Their conclusion was based on optical and X-ray diffraction studies of texture and crystallinity. Trace element analysis of the sediment and the proposed nearby source rocks might demonstrate whether or not part of the finer portion is of local ori. gin. The postulated local source rocks for the MidAtlantic Ridge sediments are ridge basalts (oceanic tholeiites) and associated metamorphic rocks (greenstones). The greenstones have been interpreted as a metamorphic product of tholeiitic basalts [5,6]. Frey et al. [7] observed that the rare earth element (REE) distributions of the basalts are not radically * Now at Great Lakes Research Division, University of Michigan, Ann Arbor, Michigan.
changed during the postulated metamorphism to greenstones. The REE distributions of these basalts and greenstones are depleted in light REE relative to the distributions observed in oceanic sediments [8] and in most continental rocks [9]. If the sedimentary minerals derived from the MidAtlantic Ridge basalts and greenstones retain a light REE depletion, then REE analyses of the sediment minerals would identify the locally derived minerals. We have analyzed the constituent phases of two surface dredge samples studied by Siever and Kastner
[3]. 2. Sample description The Chain 44 Dredge 3 sample is from the median valley region at 22°38.01'N from 45°0.7 to 44°58.8'W at a depth of 2400-3400 m. This sample was chosen for two reasons: (1) the coarse-fraction contains mineral and rock fragments of local origin; (2) the presence of well-crystallized montmoriUonite. The THV 15 sediment was collected in the median valley at 22°47.5 from 45 ° 11.4 to 45 ° 12.2'W at a depth of 2460-2630 m. It is an unusual sample, consisting primarily of amorphous material in the less than 10ta fraction.
R.A. Copeland et al., Origin of clay minerals 3. E x p e r i m e n t a l
187
data, one c o n t a i n e d a b o u t 80% chlorite, 10% kaolinite and 10% illite and the o t h e r a b o u t 65% m o n t m o r i l l o n ite, 20% chlorite, 10% illite and 5% kaolinite. Since the T H V 15 sample was primarily amorphous, electrophoresis separation was impossible. A less than 10/z fraction was separated, equilibrated 10 min w i t h 25% v/v acetic acid, washed and analyzed w i t h o u t further t r e a t m e n t . All samples were analyzed for Fe and R E E b y instrumental n e u t r o n activation analysis [ 12]. Small sample size (1 or 2 mg) and interference f r o m o t h e r elements limited our R E E analyses to data for La, Ce, Eu, Dy and Lu. The values r e p o r t e d in table 1 are believed accurate within the error limits given. Error limits were based on c o u n t i n g statistics, reproducibility and interferences. C o n c u r r e n t analysis o f W-1 and G-1 gave results within the range o f previously observed values for
The C h 4 4 sample was separated i n t o a greater than 63/~ and a 1 - 1 0 / a fraction b y sieving and centrifuging. E a c h fraction was t h o r o u g h l y washed w i t h distilled d e i o n i z e d water. Samples o f unaltered glass, chlorites, and a yellow-orange m o n t m o r i l l o n i t e ( n o n t r o n i t e ) were picked f r o m the coarse fraction. In addition, a greenstone f r a g m e n t f r o m the same dredge was crushed and the chlorite was separated. The 1-10bt fraction was equilibrated for 10 min. w i t h 25% v/v acetic acid to r e m o v e calcium carbonate and m e t a l h y d r a t e s and t h e n b u f f e r e d in 2 X 10-4M sodium carbonate. Such an acid t r e a t m e n t does n o t appreciably dissolve the clay minerals [ 1 0 ] . The clay minerals were separated b y c o n t i n u o u s particle electrophoresis [11 ]. T w o principal fractions (1 mg) were collected for analysis. O n the basis o f X-ray diffraction
Table ! Fe (%) and REE (ppm) abundances. Sample Ch44Dr3: Chlorite from greenstone Iron-richchloritea(>63/~) Magnesium-richchloriteb(>63/a) 1-10/achlorite c Palagonite Nontronite 1-10~tMontmoriUonite d THV15: Amorphous ( < 10/~) Continental clays: Belle Fourche montmorillonite f Mainemontmorillonite Metamorphic chlorites: Swedish chlorite Ural Mountains chlorite Standard rocks: G-1 (granite) G-1 literature g W-1 (diabase) W-1 literature g a
Fe
13.8+0.6 10.0-+0.5 8.8-+0.4 5.4+0.4 10.2 +- 0.6 24.2 +- 1.5 14.4-+0.9
La
5.2 3.2 4.7 3.0
C¢
Eu
Dy
-+ 0.7 +-0.7 -+ 0.7 -+ 0.3 5 -+ 1 3 -+ 1 43-+6
_e 18 -+ 6 92-+10
1.2 1.7 1.6 1.2 1.9 2.2 3.1
-+0.2 -+0.2 -+0.2 -+0.4 -+ 0.2 -+ 0.3 -+0.6
4-+1 5-+1 4-+1 7 -+ 2 9 -+ 2 8-+3
0.45 0.45 0.54 0.7 0.65 1.1 1.3
-
43 -+ 3
52 -+ 10
1.6 -+0.2
6 -+ 1
0.46 -+0.06
-
65 -+4 5.5 -+ 0.7
130 -+ 20
0.75 -+ 0.12
8 -+ 1
0.48 -+ 0.06
-
0.5
-
0.39 -+ 0.06 0.11 -+ 0.05
-
1.6 -+0.2 1.35 6.9-+0.7 7.71
123-+6 85 --110 14-+3 9.31 - 13.5
-
-+0.1
+0.04 -+0.07 -+0.05 -+0.2 -+ 0.08 -+0.2 -+0.3
-
0.3
0.06 -+0.03 0.15 -+ 0.008
-
0.05 -+0.02 0.010 -+0.005
1.6 -+0.3 1.04 - 1.36 1-+0.1 0.95 --1.29
-
0.18 0.12 0.32 0.325
Sample includes 10-20% actinolite. Some Mg-rich chlorite surrounds an inner core of Fe-rich chlorite. c Contains 20% illite and kaolinite. d Contains 15% illite and kaolinite. All values have been corrected for a 20% 1-10~ chlorite contamination. e ( - ) indicates not determined. f Tb + 1.7 _+0.4, y b = 3 + 1. g Fe data from [ 2 3 ] . Ranges of REE data from [ 2 4 ] . b
Lu
-+0.1
-+0.02 - 0.17 -+0.03 - 0.353
188
R.A. Copeland et al. Origin o f clay minerals
W-l, but our data for G-1 are systematically too high by 10-20% (table 1). The reasons for this discrepancy are unknown. A possible systematic error will not affect the following discussion which is based only on relative abundances.
4. Chlorites The likely sources of the coarse-grained chlorites in Ch44 Dr3 are the ridge greenstones [3]. Microprobe analyses of chlorites in ridge greenstones indicate about equal amounts of FeO and MgO (~ 20%) [5]. Our Fe results for a chlorite separated from a Ch44 Dr3 greenstone indicate a similar Fe abundance (18% FeO, table 1). Ch44 Dr3 chlorites have varying Fe/Mg ratios. Seiver and Kastner [3] proposed an alteration sequence from fresh dark-green chlorites (Fe-rich) to brownish-green chlorites (Mg-rich). Our optical examination indicated that green iron-rich chlorites were sometimes mantled by brown-green magnesium-rich chlorite. Fig. 1 outlines a possible alteration sequence. Iron abundances decrease in this proposed sequence (table 1). The reported iron abundances for the Ch44Dr3 chlorites are uncertain because of the impurity of the
~ PALAGONITE
BASAL~ TS
THOLEIITIC
GREENSTONES (ORIGINAL IRON-RICHCHLORITE)
i
IRON- RICH CHLORITE
YELLOW-ORANGE NONTRONITE
MAGNESIUM- RICH CHLORITE
~FINE
SEDIMENT/ ( I- IO/J.CHLORITE) ( I- IO/J. MONTMORILLONITE)
Fig. 1. Postulated alteration sequence important in deriving the clays of Ch44 Dr3 sediment.
separates mentioned in table 1. Nevertheless, the freegrained chlorite is clearly deficient in iron compared to the greenstone chlorite. This observation of iron depletion in fine-grained chlorites contrasts with the conclusions of Biscaye [1], and Griffin et al. [2]. Utilizing X-ray diffraction data, they concluded that deep sea sedimentary chlorites are consistently iron enriched. For example, Griffin et al. [2], using a semiquantitative X-ray technique, estimated that chlorites in deep-sea sediments have 2.5-4.5 heavy atoms occupying the 6 octahedral sites. This heavy atom content implies FeO contents o f > 20%. Biscaye [13] did report that chlorites from some Mid-Atlantic Ridge sediments may contain lower amounts of iron. Iron-rich chlorite may react with the marine environment either through an iron/magnesium exchange with sea water, or through oxidation-reduction changes: the latter mechanism has been observed in the reactions of synthetic micas [14]. In a simple exchange process, the chlorites should not alter except for changes in refractive indices and in intensities of 001 diffraction peaks. In an oxidation reaction, the Al/Si ratio could also change, forming a more aluminous or siliceous material depending on the initial composition. Table 2 indicates the chlorite X-ray properties, refractive indices, and chemical parameters which can be estimated from this data. The choice between mechanisms is not clear. Although variations in doo~ and refractive index are observed, the Al/Si ratio is constant within limits of error. The brownish-green chlorite appears to be a mixture (Mg-rich) of two phases. The 001 diffraction peaks are broadened compared to the green (Fe-rich) chlorite. The anomalously low refractive index is consistent with the oxidation process, but the 001 line broadening could result from either the oxidation or the exchange mechanism. The observed Fe abundance trends are confirmed by semiquantitative techniques for estimating the fraction of Fe atoms in the octahedrai sites (table 2). The method utilizing doo~ intensity ratios [I 5] has not been used for the Ch44 Dr3 coarse-grained chlorites since the assymetric correction factors (loo3/Ioo5) are unreasonable. This technique was used on a marine chlorite from a sediment far from the Mid-Atlantic Ridge (AII32, core 22, 44°44'N, 44°05'W). The cal-
R.A. Copeland et aL, Origin o f clay minerals
189
Table 2 Chlorite optical and X-ray properties.
11002
+
Fe/2: octa. sites
1004
20(060) doo1
I.R. (mean)
2AIlV 3I.R. 1Ioo1 2do6o
1oo3 corr
Ch44 Dr3 Iron-rich chlorite (>63u) 59.8 ° Mg-rich chlorite (>63u) 60.0 ° 1-10/~ chlorite 60.1 ° At111-32 Core 22 (26-33 cm) -
14.23 + 0.01 14.25 -+0.03 14.21 + 0.05
5.3 5.0 2.82
1.618 + 0.002 1.570 + 0.002 1.610
14.25 + 0.02
6.28
-
1.10-+0.03 0.42 1.09 + 0.09 1.10 +0.06 0.25 -
0.10
0.27 0.15 0.09
observ. 0.18 0.15 0.09
0.53
1. Petruk [ 15], Ioo3has not been corrected for the coarse chlorites of Ch44 Dr3. 2. Brindley [16]. 3. Albee [25]. culated fraction o f Fe atoms in octahedral sites is in the range observed by Griffin et al. [2]. The (Fe/Z octa. sites) ratios calculated from do6o [16] agree best with the observed Fe abundances. All the indirect methods demonstrate the low Fe content of the l - I 0# chlorite in the Ch44 Dr3 sample. This chlorite differs in composition from those commonly found in pelagic sediments [2]. Fig. 2 shows the REE data for the four chlorites outlined in fig. 1. The two coarse-grained chlorites which appear to be locally derived [3] have the light REE depletion characteristic of the parent greenstones. This depletion is indicated by La/Lu ratios o f 7.1 and 8.7 compared to a typical sediment value of 65 [17]. Fig. 2 also shows the REE data for the 1 - 1 0 # chlorite separated from the sediment by electrophoresis. The origin o f this fine-grained chlorite is uncertain. It has a La/Lu ratio of 4.3 which is consistent with its derivation (fig. 1) from the coarser local chlorite. All four chlorites have similar absolute REE abundances. The known impurities in some o f the chlorite separates (table 1) have not caused significant changes in the abundances. The duplication (within error limits) of REE distributions in the ridge chlorites suggests, but does not conclusively prove, a local origin for the 1 - 1 0 # chlorite. Two other possible explanations o f the similarity in REE distribution are: (1) The chlorites have REE contents in equilibria with sea water, (2) The chlorites have a characteristic crystal chemical effect o f dis. crimination against the larger REE. The expected REE content o f chlorites in equili-
ioo 80 SO 50 40
a=
• + A o
NORTH ~'% AMERICAN ~ SHALES ~
= = = =
GREENSTONE CHLORITE IRON-RICH CHLORITE MAGNESIUM-RICH CHLORITE I - I 0 / ~ CHLORITE
z
~ 3o ~ 2o br~
g
-
.
L~ I Lo
_.
.
.
GREENSTONE CH. 4 4 - 3 - 2 L Eu
L Dy
L Lu
Fig. 2. Comparison diagram for the chlorites associated with the Ch44 Dr3 sediment. Also shown are data for a Ch44 Dr3 greenstone (3-2 from ref. [7] ) and composite results for shales and ocean ridge basalts [7,9]. Chondrite values from[9]. brium with sea-water is difficult to evaluate. Seawater characteristically has La/Lu ratios of 8 to 30 [ 18]. Crystal chemical arguments for chlorite would suggest that equilibrium La/Lu ratios in chlorite should be lower than in sea-water, but the postulated high stability of heavy REE complexes [19] in sea water would tend to increase the La/Lu ratio in coexisting phases. Absolute REE abundances in the chlori. tes are l06 times those in sea water. If this reflects an equilibrium situation, much higher mineral-aqueous solution distribution coefficients must exist in sea water than those experimentally determined for the REE partitioning between silicate minerals and pure water [20]. To obtain information about possible crystal chemical discrimination against the light REE, we
190
R.A. Copeland et aL, Origin o f clay minerals
analyzed two chlorites from metamorphic rocks for REE (table 1). Both of these chlorites have lower REE abundances than the chlorites from Ch44 Dr3. However, in all six chlorites the La/Lu ratios are low (4 to 12) relative to the typical sedimentary value of 65. Although we do not have information about the phases coexisting with these metamorphic chlorites, it is clear that a crystal effect is possible. The low Fe abundances and REE data suggest that the Ch44 Dr3 fine-grained chlorites are locally derived, but our data are insufficient to prove a local origin. Fe, Mg and REE analyses of marine chlorites from non-ridge areas could provide pertinent data.
,200
i I I[ ~q'~ c.h 1001 -£1 ~ .
sol-
I
E: 7 0 J c~ 6 0 / -
T
l
~
L
zo'. (
$. f /
Lo Ce
i I o = i-lOFt MONTMORILLONITE A = THV 15 AMORPHOUS • = COARSE NONTRONITE
+ = PALAGONITE
~-
I
--
U
~
1
Eu
lIT~ - - = ,rl
Oy
z
,z-
r1
Yb Lu
5. Montmorillonite
Fig. 3. Comparison diagram for phases which may have been precursors of the fine-grained(1-10tO montmorillonite. Chondrite values from [9].
A proposed sequence for the formation of montmoriUonite is shown in fig. 1. Red to brown glass (palagonite) is common on the chilled margins of ridge tholeiitic basalts [6], and is abundant in the coarse sediment fraction of Ch44 Dr3. A coarsegrained (> 63/a) yellow-orange montmorillonite (nontronite, 24.2% Fe) is also abundant in the sediment, forming directly as an alteration product of the palagonite. It may also be related to the montmorillonite (saponite) found in the Ch44 Dr3 greenstones [6]. The transition between nontronite and 1-10/a montmoriUonite is a possibility which will be discussed. The iron content (20.6% Fe2Oa) of the fine-grained montmorillonite is higher than the range (7-15%) observed in oceanic montmoriUonites [2]. Fig. 3 shows the REE data for the palagonite, nontronite, THV15 amorphous material and the Ch44 Dr3 1-10/z montmorillonite. The light REE are relatively depleted in the palagonite and nontronite (La/Lu = 7.7 and 2.7). The 1-10# montmorillonite has a La/Lu ration of 33. This light REE enrichment is not caused by the iUite-kaolinite contamination since similar contamination levels in the fine-grained chlorite did not cause such enrichment. The absolute abundances of the REE are greater in 1-10/~ montmorillonite than in the chlorites (table 1). In the 1-10/a fraction of Ch44 Dr3 less than 30% of the sediment is montmoriUonite (estimated from X-ray diffraction data), yet more than 80% of the total REE in the 1-10/~ fraction is contained in the montmoriUonite fraction. This indicates
a greater ease of substitution of rare earths into montmorillonite than into chlorite. It is probable that the REE in montmorillonite are strongly bound in the interlayer cation positions, and will not readily exchange with sea-water. Four sources exist from which the 1-10/.t montmorillonite may have originated. First, it may be a product of the direct mechanical breakup of nontronite. Second, it may originate directly from palagonite. Third, it may crystallize from amorphous material. Finally, it may be continental in origin. If the 1-10tz montmorillonite originated from the palagonite or nontronite, considerable amounts of La and Ce must be introduced in the process. There is no obvious source for these elements. Sediments predominantly amorphous (THV 15) in the < 10# range occur near Ch44 Dr3. The origin of this amorphous material is uncertain, but it has been interpreted as an alteration product from volcanic glass and ash [3,21 ]. The THV 15 amorphous material is relatively enriched in the light REE (La/Lu = 94). In this respect it is a more suitable parent for the finegrained montmoriUonite than the nontronite or palagonite. Amorphous material is much less abundant than montmoriUonite in Mid-Atlantic Ridge sediments [3,21 ]. Thus the amorphous material is an unlikely parent unless the conversion to montmorillonite is rapid. Hydrothermal heating experiments at 250°C and 2 kbar for one week have not converted the amorphous material to montmorillonite. As a result
R.A. Copeland et al., Origin o f clay minerals
we conclude that light REE enrichment is not sufficient evidence to identify the amorphous material as a precursor to the Ch44 Dr3 fine-grained montmorillonite. Two montmorillonites from continental occurrences have also been analyzed for REE (table 1). The La/Lu ratios are quite different (18 and 135). These extreme values span the La/Lu range found in continental rocks such as granites and sediments (La/Lu = 6 0 - 8 0 , [9] ). The absolute REE abundances in the two continental montmorillonites and the Ch44 Dr3 fine-grained montmorillonite are similar to those found in shales [17]. It seems likely that montmorlllonite is the dominant host mineral for the REE in most shales and pelagic sediments [8]. Since the Ch44 Dr3 fine-grained montmorillonite has a La/Lu ratio and REE abundances within the ranges observed in continental montmoriUonites, we suggest that this material has a continental origin. The data presented demonstrate that the coarse mineral fractions o f ridge sediments have REE abundances characteristic o f their source rock. Further research is necessary, but it is also possible that the finegrained chlorite fraction retains a parent REE distribution despite changes in iron abundances. Since the REE distributions in continental detritus are quite d i f ferent from those in oceanic ridge rocks [7], the REE distributions of pelagic chlorites and montmorillonites may be a valuable indicator of provenance. Furthermore, because unique trace element abundances characterize oceanic ridge rocks [22], trace element studies of sediment phases derived from an oceanic ridge may be a useful method for studying the history of an oceanic ridge system. The sediments immediately overlying basalt in Joides cores (Legs 2 and 3) might be particularly informative.
Acknowledgement
The authors thank Drs. Vaughn T. Bowen and Geoffrey Thompson o f Woods Hole Oceanographic Institution for supplying the samples used and offering many helpful suggestions. We also thank Prof. H. Holland and Dr. James Drever who made available time and equipment at Princeton University. This research was supported by the U.S. Office of Naval Research under NR 083-157 ONR Contract Nonr.
191
1841 (74). Neutron irradiations were made at the Massachusetts Institute of Technology nuclear reactor. The samples were collected on cruises o f the Woods Hole Oceanographic Institution and the Scripps Institute of Oceanography. These cruises were supported variously by the Atomic Energy Commission, the National Science Foundation, and the Office of Naval Research.
References
[1] P.E. Biscaye, Mineralogy and sedimentation of recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans, Bull. Geol. Soc. Amar. 76 (1965) 803. [2] J.J. Griffm, H. Windom and E.D. Goldberg, The distribution of clay minerals in the world ocean, Deep Sea Res. 15 (1968) 433. [3] R. Siever and M. Kastner, Mineralogy and petrology of some Mid-Atlantic ridge sediments, J. Marine Res. 25 (1967) 263. [4] P.J. Fox and B.C. Heezen, Sands of the Mid-Atlantic Ridge, Science 149 (1965) 1367. [5] W.G. Melson and T.H. Van Andel, Metamorphism in the Mid-Atlantic Ridge, 22°N. latitude, Marine Geol. 4 (1965) 165. [6] W.G. Melson, G. Thompson and T.H. Van Andel, Vulcanism and metamorphism in the Mid-Atlantic Ridge 22°N latitude, J. Geophys. Res. 73 (1968) 5925. [7] F.A. Frey, M.A. Haskin, J.A. Poetz and L.A. Haskin, Rare earth abundances in some basic rocks, J. Geophys. Res. 73 (1968) 6085. [8] T.R. Wildeman, L.A. Haskin, Rare-earth elements in ocean sediments, J. Geophys. Res. 70 (1965) 2905. [9] L.A. Haskin, M.A. Haskin, F.A. Frey and T.R. Wilder man, Relative and absolute terrestrial abundances of the rare earths, in: Origin and Distribution of the Elements, ed. L.H. Ahrens (Pergamon, New York, 1968) p. 889. [10] R. Chester and M.J. Hughes, A chemical technique for the separation of ferromanganese minerals, carbonate minerals and absorbed trace elements from pelagic sediments, Chem. Geol. 2 (1967) 249. [ 11 ] J.I. Drever, The separation of clay minerals by continuous particle eleetrophoresis, Am. Mineralogist 54 (1969) 937. [12] G.E. Gordon, K. Randle, G. Goles, J. Corliss, M. Beeson and S. Oxley, Instrumental activation analysis of standard rocks with high resolution 3,-ray detectors, Geochim. Cosmochim. Acta 32 (1968) 369. [13] P.E. Biscaye, Distinction between kaolinite and chlorite in recent sediments by X-ray diffraction, Am. Mineralogist 49 (1964) 1281.
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R.A. Copeland et al., Origin o f clay minerals
[14] D.R. Wones and H.P. Eugster, Stability of biotite: experiment, theory and application, Am. Mineralogist 50 (1965) 1228. [ 15 ] W. Petruk, Determination of the heavy atom content in chlorite by means of the X-ray dfffractometer, Am. Mineralogist 49 (1964) 61. [16] G.W. Brindley, Chlorite minerals, in: The X-ray Identification and Crystal Structures of Clay Mineral, ed. G. Brown (London, Mineral. Society, 1961) p. 268. [17] L.A. Haskin, T.R. Wildeman, F.A. Frey, K.A. Collins, C.R. Keedy and M.A. Haskin, Rare earths in sediments, J. Geophys. Res. 71, 24 (1966b) 6091. [18] O.T. Hogdahl, S. Melson and V.T. Bowen, Neutron activation analysis of lanthanide elements in sea water, in: Trace Inorganics in Water, Advances in Chemistry Series 73, ed. R.F. Gould (Amer. Chem. Soc., Washington, D.C., 1968) p. 308. [19] E.D. Goldberg, M. Koide, R.S. Schmitt and R.H. Smith, Rare-earth distributions in the marine environment, J. Geophys. Res., 68, 14 (1962) 4201.
[20] R.L. Cullers, L.G. Medaris and L.A. Haskin, Gadolinium: Distribution between aqueous and silicate phases, Science 169 (1970) 580. [21] J.W. Murray, The clay mineralogy of marine sediments in the North Atlantic at 20°N latitude, Earth Planet. Sci Letters 10 (1970) 39. [22] A.E. Engel, C.G. Engel and R.G. Havens, Chemical characteristics of oceanic basalts and the upper mantle, Bull. Geol. Soc. Amer. 76 (1965) 719. [23] M. Fleischer, U.S. Geol. Surv. Standards-I. Additional data on rocks G-1 and W-l, 1965-1967; Geochim. Cosmochim. Acta 33 (1969) 65. [24] H. Higuchi, K. Tomura, N. Onuma and H. Hamaguchi, Rare earth abundances in several geochemical standard rocks, Geochim. J. 3 (1969) 171. [25] A.S. Albee, Relationships between the mineral association, chemical composition and physical properties of the chlorite series, Am. Mineralogist 47 (1962) 870.