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The distribution of Pb, Ag, Sn, Tl, and Zn in sediments on active oceanic ridges
Marine Geology - ElsevierPublishing Company, Amsterdam - Printed in The Netherlands
T H E D I S T R I B U T I O N OF Pb, Ag, Sn, Tl, A N D Zn IN SEDIMENTS O N ACTIVE OCEANIC R I D G E S 1 ARTHUR HOROWITZ Institute of Marine and Atmospheric Sciences, University of Miami, Miami, Fla. (U.S.A.)
(Received February 23, 1970) (Resubmitted May 5, 1970)
SUMMARY
Ninety-five sediment samples, taken from traverses across active oceanic ridges, were analyzed by emission spectrography for Pb, Ag, Sn, Tl, and Zn. The concentration patterns produced from these analyses indicate that processes associated with active oceanic ridges partially affect the distribution of Pb, T1, and Zn, while the distribution of Ag is affected only in the Pacific and western Indian Ocean, and Sn distribution is not related to any active ridge process. The covariation between distance from a ridge and concentration indicates that the ridge effects are not more than l0 ~o. Average concentrations (weighted by sedimentation rates) were determined for Pb, Ag, Sn, T1, and Zn in parts of the Pacific, the Atlantic, and the Indian Ocean. On the basis of the high elemental concentrations of Pb, T1, and Zn in the Pacific, the intermediate concentrations in the Indian Ocean, and the low concentrations in the Atlantic, it is inferred that the East Pacific-Antarctic Ridge system is the most active, the north Mid-Atlantic Ridge is the least active, and the Indian Ocean Ridge system is of intermediate activity; all of which seems to be in accord with presently available geophysical data for the same regions. INTRODUCTION Geochemical balance calculations indicate that pelagic sediments contain larger concentrations of certain elements than can be attributed to continental weathering (GOLDSCHMIDT, 1938; RUBEY, 1951; WEDEPOHL, 1960; TUREKIAN and WEDEPOHL, 1961; HORN and ADAMS, 1966). HORN and ADAMS (1966) calculated geochemical balances for 55 elements but failed to bring Cl, S, Mn, Br, B, Pb, As, Mo, I, Se, and Sb into balance. They conclude that "a significant percentage of their total mass in the sedimentary and oceanic domain were derived from a 1 Contribution No. 1248 from the University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, Miami, Fla. (U.S.A.). Marine Geol., 9 (1970) 241-259
242
A. HOROWITZ
volcanic source". This suggestion is not a new one: in 1878 C. W. yon Gtimbel postulated that the Mn in manganese nodules is delivered by hydrothermal springs. Similar explanations have been given by REVELLE and EMERY (1951) and by ARRHENIrOS and BONATTI(1965) for the origin of barite in some sediments in the Pacific. SKVORNYAKOVA (1964) suggested that volcanic sources are responsible for the formation of ferromanganoan sediments. BOSTR/)M and PETERSON (1966, 1969), BOSTROMet al. (1969), BOSTROMand FISHER (1969), BOSTR()Mand VALDES (1969), and FISHER and BOSTR/SM(1969) found that Fe, Mn, V, Cr, As, Hg, Cd, U, and B have their largest concentrations in areas of high heat flow; whereas A1, Si, Ti, Mo, and Co show low concentrations in the same sediments. Pb, Ag, Sn, T1, and Zn are geochemically volatile according to the data published by R1NGWOOD (1964) and LARIMER (1967). These elements may have their origin in the mantle and may be brought to the surface by degassing. Judging from a comparison of crustal and mantle abundances with meteoritic concentrations, Pb, Ag, Sn, Tl, and Zn appear to have migrated upward from the mantle, at least to some extent, during the geologic history of the earth (POLDERVAART, 1955; RINGWOOD, 1964; TAYLOR, 1964; LARIMER,1967). Production of heat and seismic activity are often manifested as volcanic and igneous activity. The highest heat flow (VoN HERZENand LANGSETH,1966) and much of the seismic activity (ISACKS et al., 1968) in the ocean floor is generally found on or near the active ridge-rise system. This system was probably formed by mantle convection cells which are active today (VINE, 1966; HEIRTZLER et al., 1968). It seems possible, therefore, that the ridge-rise system could serve as an exit for volatile elements from the mantle and crust (BosTR/JM and PETERSON, 1966, 1969; etc.). To test this hypothesis, a series of 95 sediment samples from traverses of some of the active ridges were analyzed for Pb, Ag, Sn, T1, and Zn (see Table I-IV for locations). METHODS Pb, Ag, Sn, TI, and Zn were analyzed with a Bausch and Lomb emission spectrograph. 20 mg of dried sample was mixed with 20 mg of graphite which contained an internal standard (Bi) and buffers, placed in a carbon electrode, and burned in an argon atmosphere for a period of 50 sec in a 20-A D.C. arc. All samples were analyzed twice and, if the reproducibility was 30 ~ or better, the values were averaged. A third determination was made if the difference was greater than 30 ~ . In most cases, the average reproducibility (percent error) was 20 ~ or better (see Table I-IV). With the analytical method employed, the detection limit was 1 p.p.m, for Pb, 0.03 p.p.m, for Ag, 0.5 p.p.m, for Sn, 0.5 p.p.m, for T1, and 1 p.p.m, for Zn. The values for Fe, Mn, V, As, and CaCO 3 come from BOSTR~M and PETERSON (1969), BOSTR(iM et al. (1969), BOSTR/JM and VALDES (1969), and K. Bostr6m (unpublished results, 1966-1969). Marine Geol., 9 (1970) 241-259
i
"~-a
2"
Location
51G 52G 56G 60G
63G 65G 66G 68G 69G 71G 72G 73G 74G
12 °39'S 12 °33'S 12 °30'S 13 °36'S 14°41'S 14°15'S 14 °18"S 14°14'S 14 °00'S
13 °32'S 13 °24'S 13 °02'S 12 °48'S
75G 76G 77G 81G 82G
14°01'S 13°54'S 14°02'S 14 °09'S 14°0YS
122°28'W 125°21"W 128°29'W 138°06'W 139°35'W
ll0°00'W lll°12'W 112°37'W 112°42'W 113°29'W 113°50'W 115°37'W 117°43'W 119°36'W
97°48'W 100°29'W 104°41'W 107°59'W
35-70 30-70 30-67 30-70 30-70
30-70 30-70 30-70 30-70 30-70 30-70 30-70 30-70 38-70
34--60 30-70 33-60 37-70
Depth in core (cm)
3,790 3,800 3,985 4,050 3,900
3,135 3,110 3,165 2,990 3,010 3,040 3,250 3,440 3,685
3,742 4,210 3,780 3,560
Water depth (m)
81 86 49 6 56
90 77 82 66 74 80 86 88 89
78 19 55 91
144 152 182 158
119 460 162 57.3 110
188 99.1 174 116 110 88.5 189 78.1 320
138 93.0 154 192
Chemical composition CaCOa Pb (%) (p.p.m.)
4.12 6.22 4.66 5.32
10.0 4.71 2.34 2.56 3.70
11.0 1.89 13.3 2.59 5.10 3.40 4.57 9.30 4.85
3.24 1.34 1.92 10.0
Ag (p.p.m.)
----
----
--
--
--
--
----
- -
6.42
8.90
2.71
104
--
--
---
Sn (p.p.m.)
3.09
16.1 34.0 12.5 15.5
21.0 6.80 14.5 4.82 15.2
--
2.40 14.6 35.5 17.1 24.5 15.5 40.5
36.6 3.44 10.6 13.6
TI (p.p.m.)
228 245 208 238
298 138 275 236 217
129
1 2 4
138 180 492 268 415 312 147
130 281 311 190
Zn (p.p.m.)
Chemical analyses of pelagic sediments, Pb, Ag, Sn, T1 and Zn (reported on a carbonate-free basis) determined by emission spectrography (analyst A. Horowitz). Values for CaCOz from BOSTROMand PETERSON (1969), BOSTR6M and VALDES (1969), BOSTR6M et al. (1969); these values were determined by gas analysis and atomic absorption (% error ~< 10%).
Average area a Average area b Average area c Area average
Risepac Risepac Risepac Risepac Risepac
Group c (non-crest region)
Risepac Risepac Risepac Risepac Risepac Risepac Risepac Risepac Risepac
Group b (crest region)
Risepac Risepac Risepac Risepac
Group a (non-crest region)
Sample
LOCATION, DEPTH IN CORE, WATERDEPTH, AND CHEMICALCOMPOSITIONOF THE RISEPAC SAMPLES
TABLE I
to
O m
Z
o
N
~.] >
"0
o" >
L,1 ',D
b,~ 4~.
xD
44°58'S 54°54'S 57°49'S 55°04'S 50°02'S 60°47'S 62°52'S 59°55'S 60°02'S 58°59% 60°07'S 57°07'S 56°03'S 57°35'S 56c'53'S 56°05'S
Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt.
76°30'W 114°42'W 115°13'W 89°44'W 159°43'W 160°13'W 159°55'W 152°45'W 145°17'W 125°02'W 109°55'W 119°40'W 119°55'W 138°58'W 139°39"W 144°49'W
3,167 3,458 4,750 4,605 4,927 3,185 2,657 2,657 3,400 4,477 4,925 4,514 3,039 2,903 2,781 2,584
depth (m)
core (cm)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Water
Depth in
1 78 2 11 1 43 47 81 28 22 1 16 77 4 77 61
CaC03 (~)
79.1
25.5 25.2 26.5 48.2 46.3 86.2 343 180 8.34 17.0 25.8 37.2 91.1 135 90,3 80.0
Pb (p.p.m.)
Chemical composition
2.02
1.59 6.07 4.36 0.48 0.69 0.37 0.72 3.55 0.57 3.51 1.35
0.87
0.64 5.50 1.00 1.20
A~ (p.p.m.)
-
2.20
-
14.6 --11.7 0.97
0.54 -1.19 6.26
Sn (p.p.m.)
4.56
0.60 -0.16 1.12 0.91 2.71 17.7 20.9 0.14 0.75 1.02 0.24 0.52 26.2
TI (p.p.m.)
~ 169
167 102 57.6 162 399 140 189 365 44.2 50.2 43.3 70.2 78.1 >600 132 79.9
Zn (p.p.m.)
Chemical analyses of pelagic sediments, Pb, Ag, Sn, TI a n d Zn (reported on a carbonate-free basis) determined by emission s p e c t r o g r a p h y (analyst A. Horowitz). Values for CaCO3 from BOSTR6M a n d PETERSON (1969), BOSTR6M a n d VALDES (1969), BOSTR6M et al. (1969); these values were determined by gas analysis and atomic absorption ( % error ~< 10%).
Area average
5- 3 11- 1 11- 4 13- 1 14- 1 14- 9 14-11 14-12 14-13 14-16 15-11 15-15 15-16 15-21 15-22 15 24
Location
Sample
L O C A T I O N , D E P T H I N C O R E , W A T E R D E P T H , A N D C H E M I C A L C O M P O S I T I O N OF T H E E L T A N I N S A M P L E S
T A B L E II
4~ 4~
.~ 7" ,~
15°15'S 33 °20'S 15°31'S 13°50'S 21 °31'S 18°21'S 27 °37'S 24 °42'S 4 °24'S 5 °34'S 5 °26'S 5 °30'S 25°05'S 14°35'S 13 °53'S 13 °09'S 13°40'S 25 °26'S
M S N 48 M S N 60 D O D O 56 D O D O 77 D O D O 110 D O D O 117 D O D O 137 D O D O 141 D O D O 195 L S D A 106 L S D A 107 L S D A 108 L S D A 139 L S D A 142 L S D A 143 L S D A 144 L S D A 145 L S D H 22
81°08'E 72 °38'E 113°45'E 91°16'E 78°01'E 62 °04'E 71 °57'E 73 °05'E 84 °43'E 63 °43'E 59°15'E 57 °56'E 104°14'E 88 °02'E 90°48'E 93 °13'E 100°20'E 57 °38'E
4,996 4,224 5,377 5,480 4,610 3,398 2,955 3,600 4,092 4,090 4,010 2,550 5,215 2,630 5,320 5,226 5,986 5,105
depth (m)
core (cm)
3-23 7-21 2-15 5- 9 3-10 6--20 4-20 4-10 5-15 4-15 4-15 4-15 4-15 dredge 9-32 5-15 8-18 6-17
Water
Depth in
1 82 2 < 1 5 88 84 85 39 78 78 80 2 89 11 2 1 1
<
CaCOa (%)
79.2
42.5 106 45.1 39.5 97.4 162 98.8 192 39.0 43.6 86.9 75.8 55.4 168 28.0 51.8 40.5 52.8
Pb (p.p.m.)
Chemical composition
0.74
--
-0.22 -0.05 0.08 7.83 3.93 -0.08 ----0.63 -0.55
Ag (p.p.m.)
0.62
0.67 -1.35 -3.08 ---3.65 ---1.29 ---1.13 --
Sn (p.p.m.)
1.62
1.38 -2.93 1.50 4.20 ---2.98 2.17 --2.39 -3.52 2.27 3.31 2.62
TI (p.p.m.)
154
49.0 91.5 188 119 115 565 128 270 112 60.4 63.6 66.3 70.4 160 29.4 122 75.2 490
Zn (p.p.m.)
Chemical analyses of pelagic sediments, Pb, Ag, Sn, T1 and Z n (reported on a carbonate-free basis) determined by emission spectrography (analyst A. Horowitz). Values for CaCOa from BOSTR6M and PETERSON (1969), BOSTR~JMand VALDES (1969), and BOSTR~M et al. (1969); these values were determined by gas analysis and atomic absorption ( ~ error ~< 10%).
Area average
Location
Sample
L O C A T I O N , D E P T H IN C O R E s ~A/ATER A N D D E P T H C H E M I C A L C O M P O S I T I O N OF TIdE I N D I A N O C E A N S A M P L E S
T A B L E IIl
to 4~
N
=.
Z
©
0 Z >
> 7t ~7 N
>
"0
t-~
I
Location
19°54'N 21°57'N 35°30'N 34°51'N 34°09'N 33 °36'N 22°42'N 32°11'N 23°01'N 31 °53'N 30°22'N 30°17'N 29 °52'N 23 °30'N 29°53'N 29°42'N 29 °24'N 23 °48'N 28 °33'N 24 °16'N
P6511-29 P6303-14 P6303-15
27°43'N 24 °27'N 24°52'N
Group b (crest region)
P6303- 7 P6303- 8 P6511- 7 P6511-10 P6511-13 P6511-16 P6303- 9 P6511-17 P6303-10 P6511-18 P6511-19 P6511-20 P6511-21 P6303-I 1 P6511 -22 P6511-26 P6511-27 P6303-12 P6511-28 P6303-13
Group a (non-crest region)
Sample
m_
37°13'W 38 °29'W 40°27'W
23°02'W 26°32'W 12°55'W 13 °00'W 13 °53'W 14 °26'W 29°49'W 18 °46'W 31°20'W 20 °01"W 22 ° 0 7 ' W 23 °42'W 24 °56'W 33 °36'W 27°51'W 28°43"W 30 °20'W 35 °10'W 33 °44'W 37 °05'W 25 25 0~0
4,838 4,451 4,600
4,282 5,270 4,867 3,740 4,109 4,173 5,564 4,418 5,700 4,474 5,051 5,337 5,426 5,970 4,450 3,093 4,672 5,837 5,0|2 4,905
depth (m)
core (cm)
0-40 0-40 25 25 25 25 0--40 25 (~40 25 25 25 25 (~40 25 25 25 0-40 25 0-40
Water
Depth in
49 43 41
57 29 26 73 56 84 3 74 < 1 62 66 53 55 --~ 1 68 82 70 2 46 36
CaC03 (%)
58.8 45.9 43.1
37.5 32.2 20.9 49.6 74.9 94.4 45.8 53.8 48.3 21.0 39.7 25.2 32.7 51.5 21.1 87.7 16.7 46.9 27.3 42.1
Pb (p.p.m.)
Chemicalcomposition
L O C A T I O N , D E P T H 1N C O R E , W A T E R D E P T H A N D C H E M I C A L C O M P O S I T I O N OF T H E A T L A N T I C S A M P L E S
T A B L F IV
0.430 0.094
0.085 0.151 0.070 0.177 0.093 0.331 0.039 0.168 --0.091 0.067 -0.054 0.127 0.260 0.189 0.060 0.070 --
Ag (p.p.m.)
1.36 2.19
2.47 4.24 1.17 -5.72 5.12 2.01 3.95 2.10 2.81 2.20 2.33 1.42 1.68 2.90 6.54 4.16 3.36 1.70 1.87
(p.p.m.)
Sn
2.19 0.85 1.62
0.85 0.99 1.41 2.70 5.40 6.06 1.16 2.99 1.10 2.02 1.79 2.12 1.84 1.58 2.27 4.82 3.23 1.45 1.18 1.02
TI (p.p.m.)
58.3 68.7 87.8
25.2 124 51.6 64.4 48.2 134 61.0 69.1 64.0 24.7 65.0 31.6 38.9 65.0 28.7 85.5 15.8 105 26.6 60.1
(p.p.m.)
In
1"4
",O --0
27°08'N 25°06'N 26°15'N 29°27'N 25°37'N 25°29"N 25°5YN 26°07'N 26°13"N
24 °01 ' N 23 °21 ' N 26 °30'N 22 °30'N 26 °20'N 22 °06'N 21 °2YN 20 °36"N 26 ° 12"N 26 °00'N 25 °44'N
53 °15'W 56 °07'W 56 °08'W 59 °29'W 60 °20'W 61 °08'W 64 °04'W 67 °08'W 68 °54'W 73 °38'W 77 °07'W
40°00'W 42 °34'W 43 °30'W 44 °40'W 46 °19'W 46 °57'W 48 °31'W 51 o13'W 52 °28'W 25 25 0-40 25 0--40 25 25 25 0-40 0-40 0-40
25 0--40 25 0~A) 0-40 25 0-40 0-40 if40 6,115 6,177 5,576 5,883 5,580 5,401 5,464 5,123 5,444 5,228 2,777
4,340 4,169 2,826 3,950 4,867 4,266 4,333 5,224 5,384 < < < <
1 1 1 1 1 1 1 16 3 26 56
69 44 85 52 58 71 52 2 1 0.057 0.051 0.036 -0.132 -0.141 0.115 0.047 0.038 0.078 12-19
43.6 57.1 38.8 45.8 10-18
0.148 ---0.108 0.123 --0.051
20.2 38.3 60.3 50.5 46.0 32.6 34.6 46.1 34.5 47.6 16.4
127 23.5 106 30.8 30.9 22.7 54.3 60.7 70.2
12-20
2.81 2.17 3.33 2.24
0.98 3.10 4.45 1.70 2.07 1.39 3.36 -2.70 2.05 3.91
-2.03 -2.15 2.83 4.68 2.23 2.68 5.10
13-20
2.27 2.53 2.25 2.31
0.74 2.25 3.78 2.32 2.45 2.65 2.52 2.02 2.67 1.78 1.23
3.12 1.17 7.12 1.24 2.05 2.58 1.51 2.44 2.90
14-25
50.5 86.5 96.0 75.8
4.50 57.0 205 52.5 112 73.7 104 104 227 96.5 18.5
143 27.5 225 25.9 37.3 41.3 54.3 126 126
Chemical analyses of pelagic sediments, Pb, Ag, Sn, TI and Z n (reported on a carbonate-free basis) determined by emission spectrography (analyst A. Horowitz). Values for CaCO3 from BOSTR6M and PEa~aSON (1969), BOSTR6M and VALDES (1969), BOSTR6M et al. (1969); these values were determined by gas analysis and atomic absorption ( ~ error ~< 10~/0).
Percent error (all samples)
Average area a Average area b Average area c Area average
P6511-34 P6511-35 P6303-22 P6511-36 P6303-23 P6511-37 P6511-38 P6511-39 P6303-25 P6303-26 P6303-27
Group c (non-crest region)
P6511-30 P6303-16 P6511-31 P6303-17 P6303-18 P6511-32 P6303-19 P6303-20 P6303-21
.-O
Ix.)
7,
c)
,.q
o Z >.
z7 N
>
>
248
n. HOROWITZ
RESULTS
Tables I-IV contain the analytical results with the concentrations of Pb, Ag, Sn, T1, and Zn reported on a carbonate free basis (to remove the dilution effect of biogenous CaCO3). The biogenic contributions (tests of dead marine organisms) appear to be negligible in comparison to the elemental concentrations determined (TUREKL~N, 1965). The element/(Al + Fe + Mn) ratios have been calculated for the Eltanin samples (results not reported) because silica is a major biogenic dilutant here, in addition to CaCO3 (ANGINO, 1966). The overall concentration patterns for these samples remain essentially the same after this treatment. The results are presented in graphical form (Fig. 1-5) with concentration on a carbonate free basis plotted against distance from a ridge crest. It is assumed 200 160~
L
E
S
120 Pb(ppm} 80
40
A 0
ooOO I Pb[ppm} ~
A
..............
,' ,
RISEPAS SAMPLES
.
I 7.
:i
r
'
- Pb{ppm)
~oo
!20
ATLANTIC SAMPLES 90
Pb(ppm) 6G
30
D
~-
,
o
Fig.1. Graphical representation of Pb concentration on a carbonate free basis (C.F.B.). The solid line is the data, the dashed line is a sliding average using three samples at a time. The distance between the samples and the ridge crest was measured from a map where the sample locations were plotted and the ridge crest (central magnetic anomaly) marked. The sample distances are marked on the x-axis. In Fig.lA and B the y-axis demarks the ridge crest. In Fig.lC and D the solid vertical lines delineate the crest region and the dashed vertical line indicates the ridge crest.
Marine Geol., 9 0970) 241 259
Pb, Ag, Sn, T1 AND Zn ON ACTIVEOCEANIC RIDGES
249
Ag(ppm) 4 2 A
," % '
o ...........
-
4
~
-
:
~
.
ELTDNSN SAMPLES
Ag(pprn)
B
,
o 12
RISEPACSAMPLES
i
Aq(ppm) 8 4 - 0
40
(ppm)
D Fig.2. Graphical representation of Ag concentration on a carbonate free basis (C.F.B.). For legend see Fig.1. that the ridge crest coincides with the central magnetic anomaly as given by HEmTZLER et al. (1968). The Risepac and Atlantic samples represent single traverses and are presented in geographical position as they would appear on a map, with the ridge crest in the center. Graphs for the Eltanin and Indian Ocean samples display concentration against distance from the ridge regardless of geographical position, because they do not fall on a single traverse. The analytical errors do not change the patterns significantly. Due to the close proximity of land to some of the Indian Ocean samples, the graph for Sn is slightly misleading. The highest Sn value is from sample D O D O 195 which is extremely close to land, but also somewhat close to an active ridge. The source of the Sn appears to be terrigenous. If the traverses are broken down into crest (b group) and non-crest (a and c groups) areas, and the concentration for each area averaged, the results are more striking. The Pb, T1, and Zn values tend to be highest in the crest areas and lower in the non-crest areas. Silver (except in the Pacific and western Indian Ocean) Marine Geol., 9 (1970) 241-259
250
A.
HOROWITZ
3O
Sn(ppm)
INDIAN OCEANSAMPLES
2O
A
o
.... /
ISl
Sn(ppm)
B !
~,
RISEPACSAMPLES
ATLANTIC SAMPLES
!
120
SFl(ppm) 40
6
F
\4
Sn(ppm)
2
0
Fig.3. Graphical representation of Sn concentration on a carbonate free basis (C.F.B.). For legend see Fig.1. and especially Sn tend to show low or minimum values in the crest samples and higher values in the non-crest samples (see Table I and IV). Comparison of element concentrations from one oceanic area to another shows the concentrations for Pb, Ag, T1, and Zn are highest in the Pacific, lowest in the Atlantic, and intermediate in the Indian Ocean. The factors separating the concentrations in the Pacific from those in the Atlantic are about 1.5 times for Pb, about 3 times for Ag, about 2.7 times for T1, and about 2 times for Zn. On the other hand, Sn has the highest concentration in the Atlantic, the lowest in the Indian Ocean, and an intermediate one in the Pacific. The overall picture probably would show Sn to be lowest in the Pacific but the results are biased by one very high Sn value from sample Risepac 63 G. The concentration of Sn in the Atlantic samples is 3 times more than in the Indian Ocean samples. In order to consider the effects of sedimentation in each of these areas, the Marine Geol., 9 (1970) 241-259
Pb, Ag, Sn, T1 AND Zn ON ACTIVEOCEANICRIDGES
T I (ppm) 25
251
""N
A 30
1
Tl(ppm) I0 B
.~
o
. '~.,,--
~
.....
.. . . . . . . . . . .
" ....................
.
-
30
L~[lppm)
'i
c
ATLANTIC SAMPLES
I I
6
T~(ppm', 4
Fig.4. Graphical representation of TI concentration on a carbonate free basis (C.F.B.). For legend see Fig.1. sedimentation rates published by K u et al. (1968) were used to give more weight to samples from areas of high sedimentation and inserted in the following equation: (sedimentation rate) x (element concentration) E sedimentation rates thus producing a sedimentation rate-weighted element concentration. The values obtained may not be exact since the published sedimentation rates do not apply to the exact areas where the core samples are located. The results are given in Table V. The only variable which can be related to ridge responsibility for concentration of the elements under study, is the distance from the crest of the ridge. A series of correlation coefficients were calculated to determine the approximate effects of active ridges on element concentration (Table VI). The results indicate a negative covariation between element concentration and distance from the ridge Marine Geol., 9 (1970) 241-259
252
A. HOROWITZ
~
400 Zn(ppm)
', i A
o
-
""
LES
"'"",
-
>600ppm 600
ELTANIN SAMPLES
Zn(ppm)
,-
200 B
o
"
~
, RISEPAC SAMPLES
!
!i
6OO
I
400
C
. . . . . . . . . .
[.
~J
Zn(ppm}
24O
ISO
Zn{ppm' 120
60 0
Fig.5. Graphical representation of Zn concentration on a carbonate free basis (C.F.B.). For legend see Fig.1.
crest for Pb, Ag, TI, and Zn, i.e., higher concentrations being closer to the ridges. The amount of covariation ranges from 4 % to nearly 10 %. Correlation coefficients were determined for all combinations of Pb, Ag, Sn, TI, and Zn in order to study the associations between these elements. Correlations of the various elements with Mn and Fe were calculated to test KRAUSKOPF'S (1956) theory of hydrous oxides of Mn and Fe acting as adsorbers for trace elements, and active ridges appear to be probable sources of Fe and Mn (SKYORNYAKOVA, 1964; BOSTROMand PETERSON, 1966; etc.). Correlations were made with As because of its known volatility (ONIsHI and SANDELL, 1955; RINGWOOD, 1964; LARIMER, 1967) and because it appears to be enriched on active ridge crests (BOSTROM and VALDES, 1969); and with V because it is enriched on active ridge crests and the data were available for most of the samples (BOSTROMand PETERSON, 1969; BOSTR6M et al., 1969; BOSTRiSMand VALDES, 1969; K. Bostr6m, unpublished results, 1966-1969). Correlation coefficients were also calculated with CaCO3 to test the hypothesis that biogenic activity (tests of dead marine organisms) does not play an important role in collecting Pb, Ag, Sn, TI, and Zn. Wherever feasible, Marine Geol., 9 (1970) 241-259
Pb, Ag, Sn, T1 AND Zn ON ACTIVEOCEANICRIDGES
253
TABLE V AVERAGE ELEMENTAL CONCENTRATION (ON A CARBONATE FREE BASIS, WEIGHTED BY SEDIMENTATION RATE) FOR PORTIONS OF THE WORLD OCEANS
Area
Equatorial and southern Pacific North Atlantic Indian Ocean
Pb (p.p.m.)
Ag (p.p.m.)
Sn (p.p.m.)
TI (p.p.m.)
Zn (p.p.m.)
123 46.9 69.0
3.74 0.088 0.75
4.21 2.49 0.67
10.4 2.39 1.88
>204 74.6 125
TABLE VI CORRELATION COEFFICIENTS FOR DISTANCE VS. CONCENTRATION
Samples
Pb
Ag
Sn
TI
Zn
No. of samples
Risepac series Eltanin samples Indian Ocean samples Atlantic Ocean samples Total (all samples)
--0.058 --0.366 --0.489 --0.175 --0.291
-0.359 --0.405 --0.302 0.127 -0.297
--0.180 --0.012 0.261 0.120 0.078
--0.192 --0.354 -0.551 -0.060 -0.212
--0.181 --0.119 --0.179 0.027 --0.194
18 16 18 43 95
correlations were determined not only for the area as a whole, but also for crest (b areas) and non-crest (a and c areas) regions to see if any interelement covariations were localized in particular areas, i.e., on or off the crest. Table VII summarizes the results. Only correlation coefficients > _ 0.700 significant on the 95 ~ level or higher are shown. The value of _ 0.700 was chosen because the square of a correlation coefficient of this value will account for about 50 ~o of the covariation (CRow et al., 1960). Positive correlations for the crest areas appeared for Pb with V; T! with Zn, Mn, Fe, and V; and for Zn with T1, Mn, Fe, V, and As; negative correlations for CaCO 3 with Pb, Sn, T1, and Zn. Off the crest, positive correlations for Pb with TI, Mn, and Fe; T1 with Pb, Zn, and Mn; and for Zn with T1 and As appeared. For the areas as a whole, positive correlations were observed for Pb with TI, Mn, Fe, and V; T1 with Pb, Zn, Mn, Fe, and V; Zn with TI, Fe, and V; negative correlations were noted for CaCO 3 with Pb and Zn. The most consistent correlations (50 ~ or more of the determinations) were positive values for Pb with TI, Mn, and Fe; for TI with Pb, Zn, Mn, and Fe; and for Zn with T1, Mn, and Fe; negative values for CaCO 3 with Pb, T1, and Zn. Marine GeoL, 9 (1970) 241-259
254
A. HOROWITZ
TABLE VII STATISTICALLY
SIGNIFICANT
Sample
Pb Ag
Risepac a Risepac b Risepac c Risepac total Eltanin total Indian total Atlantic a Atlantic b Atlantic c Atlantic total
CORRELATION
COEFFICIENTS
Ag Sn
TI
Zn
Sn
Sn TI
Zn
TI
Zn
TI
Mn
Zn
Pb
**
Ag
Sn
TI
**
**
?
?
*
?
**
**
**
•
9
*
*
**
**
Zn
*
9
*
*
Blank ....... -: L 0.700 or not significant; ? == ~ 0.700 to ± 0.740; * = k 0.741 to + 0.899; ** == ~: 0.900 to -E 0.999. Symbols underlined: significant on 9 5 ~ level; all others significant on 9 9 ~ level. The letters N.D. indicate that the correlation was not calculated due to insufficient As data.
DISCUSSION The results indicate that the elements in question can be divided into two groups, the first c o n t a i n i n g Pb, TI, Zn, and sometimes Ag, and the second g r o u p c o n t a i n i n g A g a n d Sn. The distribution p a t t e r n s for Pb, T1, and Zn (except for T1 in the I n d i a n Ocean and Pb in the Risepac series) consistently show peaks in the crest regions o r areas o f high heat flow. The same p a t t e r n emerges from concentration averages for the crest (b group) a n d non-crest (a a n d c g r o u p s ) r e g i o n s . C o r r e l a t i o n coefficients for distance from the crest and c o n c e n t r a t i o n indicate a relationship between the ridges a n d the a p p e a r a n c e o f high c o n c e n t r a t i o n s o f Pb, TI, a n d Zn. These same elements also correlate well with Fe, M n , a n d V, which p r o b a b l y have a source on active oceanic ridges. Possibly Pb, TI, a n d Zn are a d d e d to deep sea sediments, to some extent, by volcanic e m a n a t i o n s from active oceanic ridges. Active ridges only affect the A g distribution in the Pacific and western I n d i a n Ocean. C o r r e l a t i o n s for distance from the crest with c o n c e n t r a t i o n s u p p o r t this view. However, A g does not correlate well with Fe, Mn, V, or As. N o n - r i d g e sources m a y account for the observed d i s t r i b u t i o n p a t t e r n s for A g in the A t l a n t i c and eastern I n d i a n Ocean. O n the o t h e r hand, Sn seems to have a purely non-ridge source in all areas studied. The d i s t r i b u t i o n p a t t e r n s and average crest and noncrest c o n c e n t r a t i o n s all tend to show low or m i n i m u m values for Sn on ridge crests. Distance vs. c o n c e n t r a t i o n correlations for Sn indicate little or no relationship between active ridges a n d the a p p e a r a n c e o f Sn. A s is the case for Ag, Sn does n o t correlate well with Fe, Mn, a n d V. Marine Geol., 9 (1970) 241-259
Pb, Ag, Sn, T1 AND Zn ON ACTIVEOCEANIC RIDGES
Fe Pb
V Ag
Sn
m
TI
? m
• * •
•
? •*
Zn
Pb
As Ag
Sn
TI
Ag
Sn
TI
Zn
*
*
**
**
**
*
**
*
?
**
**
*
*
N.D. N.D. N.D. N.D.N.D. *
N.D.
? •
Pb
• *
? **
Zn
m *
?
*
255
N.D.
N.D.
N.D.N.D.
N.D. N.D. N.D. N.D.N.D.
?
It should be pointed out that volcanic emanations from active oceanic ridges are not the only sources for Pb, Ag, TI, and Zn. The greatest concentration of these elements are derived from terrigenous sources such as continental outwash, windborn dust, glacial marine outwash, biogenous sources, cosmic sources, deposition and scavenging from sea water (including authigenic mineral formation), post-depositional alteration and migration of material buried in sediments, and submarine weathering of emplaced rocks. The ridges could probably not be expected to deliver more than 1 0 ~ of the element concentrations judging from the correlations for distance from the crest vs. element concentrations which indicated a covariation of from 4 ~o to 10 ~ . It is possible that the ridges supply Pb, Ag, Sn, T1, and Zn to pelagic sediments in all oceans but the other sources provide so much material that the ridge effects cannot be observed, as in the case of Pb in the Risepac series and T1 in the Indian Ocean. The high negative correlations of CaCO3 with Pb, T1, and Zn, and CaCO 3 with Ag in the Pacific, indicate that the concentration of these elements on active ridges probably is not due to deposition of skeletal remains. They also cast doubt on the theory that winnowing (KuENEN, 1950) is the cause of the observed concentration maxima. The bulk of CaCO3 in pelagic sediments is commonly larger than the clay size fraction and if winnowing were a factor, it would be expected that the finer clay particles would be removed while the coarser fraction remained behind. The negative correlations seem to indicate that the coarser fraction was removed, thus indicating that winnowing is not likely to have occurred, or, at least, did not cause the observed concentration maxima. Marine Geol., 9 (1970) 241-259
256
A. HOROWITZ
As a first approximation, the concentrations of Pb, Ag, Sn, Tl, and Zn listed in Table V are suggested as the oceanic sediment averages for the equatorial and southern Pacific, the Indian Ocean, and the North Atlantic. The elements that may be added to the sediments by vulcanism on active oceanic ridges all have their highest concentrations in the Pacific, with intermediate concentrations in the Indian Ocean, and lowest concentrations in the Atlantic. These differences may be a function of non-biogenic sedimentation rates which are highest in the Atlantic, intermediate in the Indian Ocean, and lowest in the Pacific, thus causing the observed differences by dilution. They cannot be a function of dilution by biogenic remains because the concentrations have been recalculated on a carbonate free basis (Table I-IV). The TI concentrations are an exception being highest in the Pacific, lowest in the Indian Ocean, and intermediate in the Atlantic. There are three possible explanations for the observed variations. The first is that the efficiency of the depositing mechanisms varies from one oceanic area to another, as observed for As (BOSTROMand VALDES, 1969) and Hg (BOSTROM and FISHER, 1969). The second is that the elements in question are brought to the surface, in part, by convection cells originating in the mantle, and are deposited on or near the crests of active ridges (this leads to the conclusion that the mantle may be inhomogeneous as far as Pb, Ag, Sn, TI, and Zn are concerned). The third can be related to HEss' (1962) theory that the active oceanic ridges are ephemeral features. If so, the quantity and composition of the material added to oceanic sediments will change as a ridge becomes older. As indicated by the concentrations of Pb, Ag, T1, and Zn, as well as the concentrations of such elements as Hg, As, Fe, Mn, etc., it appears that the East Pacific-Antarctic Ridge system is the most active, the Mid-Atlantic Ridge north of the equator is the least active, and the Indian Ocean Ridge system is of intermediate activity. The estimation of ridge activity according to elemental concentrations seems in accord with the geophysical data now available for the active ridge areas under study. The heat flow in the Pacific Ocean floor where the Risepac samples were taken is the highest, whereas that in the North Atlantic where the P6511 and P6303 samples were taken is the lowest and the Indian Ocean samples come from areas of intermediate heat flow (VON HERZEN and LANGSETH, 1965). The same correlations appear for sea-floor spreading rates. The spreading rate for the Risepac sample area is 6 cm/year, for the Eltanin sample area the average rate is 3.66 cm/ year, for the Indian Ocean the average rate is 2.03 cm/year, and for the North Atlantic the average rate is 1.33 cm/year (HEIRTZLERet al., 1968). It appears that the geochemical data for ridge derived elements mirrors the geophysical data. The higher the heat flow in a region, and the faster the spreading rate, the higher the concentration of ridge derived elements. If the activity of a ridge is the controlling factor in the ability of a ridge to add Pb, Ag, Sn, Tl, and Zn to the sediments, it could be maintained that the activity of all ridges is too low to bring Sn to the surface; the East Pacific-Antarctic Rise and the western Indian Ocean Ridge system Marine Geol., 9 (1970) 241-259
Pb, Ag, Sn, TI AND Zn ON ACTIVE OCEANIC RIDGES
257
are still sufficiently active to supply Ag contrary to the northern Mid-Atlantic Ridge which is too inactive. The northern Mid-Atlantic Ridge, in fact, appears so inactive that the Zn pattern shows almost no effect from ridge additions. The correlation coefficients calculated for Pb, Ag, Sn, T1, and Zn with Mn and Fe showed statistically significant correlations for Pb, T1, and Zn with Mn and Fe, thus lending support to the theory that these elements may be concentrated, in part, by adsorption on hydrous oxides of Mn and Fe as suggested by KRAUSKOPF (1956). Silver and Sn did not show any correlations with Mn and Fe. Co-' precipitation probably cannot explain the high correlations between Pb, TI, and Zn with Mn and Fe, as well as correlations between TI and Zn, Pb and TI, etc. because of large charge differences or incompatible ionic radii.
CONCLUSIONS
(1) The distribution of Pb, T1, and Zn is affected by processes connected with active oceanic ridges in all areas studied, while Ag distribution is affected only in the Pacific and western Indian Ocean and the distribution of Sn seems unaffected by processes on active oceanic ridges. (2) According to the concentrations of Pb, Ag, T1, and Zn, the East PacificAntarctic Ridge system is apparently the most active of the ridges studied, the Indian Ocean Ridge system is of intermediate activity, and the northern MidAtlantic Ridge is the least active. This seems to agree with the geophysical data for these areas. (3) The ridges appear to contribute no more than 10 %, and probably less, of the total concentration of Pb, Ag, TI, and Zn on active ridges. (4) Winnowing apparently has little or no effect in causing the observed concentration maxima of Pb, Ag, T1, and Zn on active ridges. (5) Lead, T1, and Zn appear to be concentrated, at least to some extent, by adsorption on hydrous oxides of Mn and Fe.
ACKNOWLEDGEMENTS
I thank Dr. Kurt Bostr~m for his advice and support throughout this research and the writing of this manuscript, and for making his samples and unpublished analytical results available. Special thanks are due to Dr. Oiva Joensuu for developing the analytical procedures used. I would also like to thank Drs. C. Emiliani, C. Harrison, J. Prospero, and S. Gartner for critically reading the manuscript and also Mr. B. Weber of the University of Miami Computing Center for running the correlation coefficients. This work was supported by National Science Foundation grants NSF GA-1356 and NSF GA-4569, the American Chemical Society PRF-#2874-A2 Marine Geol., 9 (1970) 241-259
258
A. HOROWITZ
and the Rosenstiel School of Marine and Atmospheric Sciences for the computer programming.
T h i s s u p p o r t is g r a t e f u l l y a c k n o w l e d g e d .
REFERENCES ANGINO, E., 1966. Geochemistry of Antarctic pelagic sediments. Geochim. Cosmochim. Acta, 30: 939-961. ARRIJENItJS, G. and BONATTI, E., 1965. Neptunism and vulcanism in the ocean. In: M. SEARS (Editor), Progress in Oceanography, 3. Pergamon, London, pp.7-23. BOSTRrM, K. and FISHER, D., 1969. Distribution of mercury in East Pacific sediments. Geochim. Cosmochim. Acta, 33: 743-745. BOSTRrM, K. and PETERSON, M., 1966. Precipitates from hydrothermal exhalations on the East Pacific Rise. Econ. Geol., 61: 1258-1265. BOSTR6M, K. and PETERSON, M., 1969. The origin of aluminum-poor sediments in areas of high heat flow on the East Pacific Rise. Marine GeoL, 7: 427~147. BOSTRt3M, K. and VALDES, S., 1969. Distribution of arsenic in deep-sea sediments and rocks. Lithos, 2(4): 351-360. BOSTRrM, K., PETERSON, M., JOENSUU, O. and FISHER, D., 1969. Aluminum-poor ferromanganoan sediments on active oceanic ridges. J. Geophys. Res., 74(12): 3261-3270. CROW, E., DAVIS, F. and MAXFIELD, M., 1960. Statistics Manual. Dover Pubt., New York, N.Y., 288 pp. FISHER, D. and BOSTRrM, K., 1969. Uranium-rich sediments on the East Pacific Rise. Nature, 224(5214): 64-65. GOLDSCnMIDT, V., 1938. Geochemistry. (After his death edited by A. MUIR). Clarendon, Oxford, 730 pp. HEIRTZLER, J., DICKSON, G., HERRON, E., PITMANIII, W. and LE PlCnON, X., 1968. Marine magnetic anomalies, geomagnetic field reversals, and motions of the ocean floor and continents. J. Geophys. Res., 73(6): 2119-2135. HESS, H., 1962. History of the ocean basins. In: A. E. J. ENGEL, H. A. JAMESand B. F. LEONARD (Editors), Petrologic Studies (volume in honor of A. F. Buddington). Geol. Soc. Am., New York, N.Y., pp. 599-620. HORN, M. and ADAMS,T., 1966. Computer-derived geochemical balances and element abundances. Geochim. Cosmochim. Acta, 30: 279-297. ISACKS, B., OLIVER, J. and SYI~ES, L., 1968. Seismology and the new global tectonics. J. Geophys. Res., 73(18): 5855-5899. KRAUSKOPF, K., 1956. Factors controlling the concentration of thirteen rare metals in sea water. Geochim. Cosmochim. Acta, 9: 1-32. Ku, T., BROECKER, W. and OPDYKE, N., 1968. Comparison of sedimentation rates measured by paleomagnetic and the ionium methods of age determination. Earth Planetary Sci. Letters, 4: 1-16. KUENEN, PH., 1950. Marine Geology. Wiley, New York, N.Y., 568 pp. LARIMER, J., 1967. Chemical fractionation in meteorites, 1. Condensation of the elements. Geochim. Cosmochim. Acta, 31: 1215-1239. ONISHL H. and SANDELL, E., 1955. Geochemistry of arsenic. Geochim. Cosmochim. Acta, 7: 1-33. POLDERVAART, A., 1955. Chemistry of the earth's crust. Geol. Soc. Am., Spec. Papers, 62: l 19-144. REVELLE, R. and EMERY, K., 1951. Barite concretions from the ocean floor. Bull. Geol. Soc. Am., 62: 707-724. RINGWOOD, A., 1964. The chemical composition and origin of the earth. In: P. M. HURLEY (Editor), Advances in Earth Science. M.I.T. Press, Cambridge., Mass., pp. 287-357. RtJBEY, W., 1951. Geologic history of sea water. Bull. Geol. Soc. Am., 62:111 l-1148. SI,ZYORNYA~OVA, I., 1964. Dispersed iron and manganese in Pacific Ocean sediments, lntern. Geol. Rev., 7(12): 2161-2174. TAYLOR, S., 1964. Abundances of chemical elements in the continental crust: a new table. Geochim. Cosmochim. Acta, 28: 1273-1286.
Marine Geol., 9 (1970) 241-259
P b , A g , S n , TI AND Z n ON ACTIVE OCEANIC RIDGES
259
TUREKIAN,K., 1965. Some aspects of the geochemistry of marine sediments. In: J. RILEY and G. SKIRROW (Editors), Chemical Oceanography. Academic Press, New York, N.Y., pp. 81-126. TUREKIAN,K. and WEDEPOHL,K., 1961. Distribution of the elements in some major units of the earth's crust. Bull. Geol. Soc. 4m., 72: 175-192. VINE,F., 1966. Spreading of the ocean floor: new evidence. Science, 154: 1405. VON HERZEN,R. and LANGSETH,M., 1966. Present status of oceanic heat-flow measurements. Phys. Chem. Earth, 6: 365407. WEDEPOHL, K., 1960. Spuren-analytische Untersuchungen in Tiefseetonen aus dem Atlantik. Geochim. Cosmochim. Acta, 18: 200-231.
Marine GeoL, 9 (1970) 241-259
T H E D I S T R I B U T I O N OF Pb, Ag, Sn, Tl, A N D Zn IN SEDIMENTS O N ACTIVE OCEANIC R I D G E S 1 ARTHUR HOROWITZ Institute of Marine and Atmospheric Sciences, University of Miami, Miami, Fla. (U.S.A.)
(Received February 23, 1970) (Resubmitted May 5, 1970)
SUMMARY
Ninety-five sediment samples, taken from traverses across active oceanic ridges, were analyzed by emission spectrography for Pb, Ag, Sn, Tl, and Zn. The concentration patterns produced from these analyses indicate that processes associated with active oceanic ridges partially affect the distribution of Pb, T1, and Zn, while the distribution of Ag is affected only in the Pacific and western Indian Ocean, and Sn distribution is not related to any active ridge process. The covariation between distance from a ridge and concentration indicates that the ridge effects are not more than l0 ~o. Average concentrations (weighted by sedimentation rates) were determined for Pb, Ag, Sn, T1, and Zn in parts of the Pacific, the Atlantic, and the Indian Ocean. On the basis of the high elemental concentrations of Pb, T1, and Zn in the Pacific, the intermediate concentrations in the Indian Ocean, and the low concentrations in the Atlantic, it is inferred that the East Pacific-Antarctic Ridge system is the most active, the north Mid-Atlantic Ridge is the least active, and the Indian Ocean Ridge system is of intermediate activity; all of which seems to be in accord with presently available geophysical data for the same regions. INTRODUCTION Geochemical balance calculations indicate that pelagic sediments contain larger concentrations of certain elements than can be attributed to continental weathering (GOLDSCHMIDT, 1938; RUBEY, 1951; WEDEPOHL, 1960; TUREKIAN and WEDEPOHL, 1961; HORN and ADAMS, 1966). HORN and ADAMS (1966) calculated geochemical balances for 55 elements but failed to bring Cl, S, Mn, Br, B, Pb, As, Mo, I, Se, and Sb into balance. They conclude that "a significant percentage of their total mass in the sedimentary and oceanic domain were derived from a 1 Contribution No. 1248 from the University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, Miami, Fla. (U.S.A.). Marine Geol., 9 (1970) 241-259
242
A. HOROWITZ
volcanic source". This suggestion is not a new one: in 1878 C. W. yon Gtimbel postulated that the Mn in manganese nodules is delivered by hydrothermal springs. Similar explanations have been given by REVELLE and EMERY (1951) and by ARRHENIrOS and BONATTI(1965) for the origin of barite in some sediments in the Pacific. SKVORNYAKOVA (1964) suggested that volcanic sources are responsible for the formation of ferromanganoan sediments. BOSTR/)M and PETERSON (1966, 1969), BOSTROMet al. (1969), BOSTROMand FISHER (1969), BOSTR()Mand VALDES (1969), and FISHER and BOSTR/SM(1969) found that Fe, Mn, V, Cr, As, Hg, Cd, U, and B have their largest concentrations in areas of high heat flow; whereas A1, Si, Ti, Mo, and Co show low concentrations in the same sediments. Pb, Ag, Sn, T1, and Zn are geochemically volatile according to the data published by R1NGWOOD (1964) and LARIMER (1967). These elements may have their origin in the mantle and may be brought to the surface by degassing. Judging from a comparison of crustal and mantle abundances with meteoritic concentrations, Pb, Ag, Sn, Tl, and Zn appear to have migrated upward from the mantle, at least to some extent, during the geologic history of the earth (POLDERVAART, 1955; RINGWOOD, 1964; TAYLOR, 1964; LARIMER,1967). Production of heat and seismic activity are often manifested as volcanic and igneous activity. The highest heat flow (VoN HERZENand LANGSETH,1966) and much of the seismic activity (ISACKS et al., 1968) in the ocean floor is generally found on or near the active ridge-rise system. This system was probably formed by mantle convection cells which are active today (VINE, 1966; HEIRTZLER et al., 1968). It seems possible, therefore, that the ridge-rise system could serve as an exit for volatile elements from the mantle and crust (BosTR/JM and PETERSON, 1966, 1969; etc.). To test this hypothesis, a series of 95 sediment samples from traverses of some of the active ridges were analyzed for Pb, Ag, Sn, T1, and Zn (see Table I-IV for locations). METHODS Pb, Ag, Sn, TI, and Zn were analyzed with a Bausch and Lomb emission spectrograph. 20 mg of dried sample was mixed with 20 mg of graphite which contained an internal standard (Bi) and buffers, placed in a carbon electrode, and burned in an argon atmosphere for a period of 50 sec in a 20-A D.C. arc. All samples were analyzed twice and, if the reproducibility was 30 ~ or better, the values were averaged. A third determination was made if the difference was greater than 30 ~ . In most cases, the average reproducibility (percent error) was 20 ~ or better (see Table I-IV). With the analytical method employed, the detection limit was 1 p.p.m, for Pb, 0.03 p.p.m, for Ag, 0.5 p.p.m, for Sn, 0.5 p.p.m, for T1, and 1 p.p.m, for Zn. The values for Fe, Mn, V, As, and CaCO 3 come from BOSTR~M and PETERSON (1969), BOSTR(iM et al. (1969), BOSTR/JM and VALDES (1969), and K. Bostr6m (unpublished results, 1966-1969). Marine Geol., 9 (1970) 241-259
i
"~-a
2"
Location
51G 52G 56G 60G
63G 65G 66G 68G 69G 71G 72G 73G 74G
12 °39'S 12 °33'S 12 °30'S 13 °36'S 14°41'S 14°15'S 14 °18"S 14°14'S 14 °00'S
13 °32'S 13 °24'S 13 °02'S 12 °48'S
75G 76G 77G 81G 82G
14°01'S 13°54'S 14°02'S 14 °09'S 14°0YS
122°28'W 125°21"W 128°29'W 138°06'W 139°35'W
ll0°00'W lll°12'W 112°37'W 112°42'W 113°29'W 113°50'W 115°37'W 117°43'W 119°36'W
97°48'W 100°29'W 104°41'W 107°59'W
35-70 30-70 30-67 30-70 30-70
30-70 30-70 30-70 30-70 30-70 30-70 30-70 30-70 38-70
34--60 30-70 33-60 37-70
Depth in core (cm)
3,790 3,800 3,985 4,050 3,900
3,135 3,110 3,165 2,990 3,010 3,040 3,250 3,440 3,685
3,742 4,210 3,780 3,560
Water depth (m)
81 86 49 6 56
90 77 82 66 74 80 86 88 89
78 19 55 91
144 152 182 158
119 460 162 57.3 110
188 99.1 174 116 110 88.5 189 78.1 320
138 93.0 154 192
Chemical composition CaCOa Pb (%) (p.p.m.)
4.12 6.22 4.66 5.32
10.0 4.71 2.34 2.56 3.70
11.0 1.89 13.3 2.59 5.10 3.40 4.57 9.30 4.85
3.24 1.34 1.92 10.0
Ag (p.p.m.)
----
----
--
--
--
--
----
- -
6.42
8.90
2.71
104
--
--
---
Sn (p.p.m.)
3.09
16.1 34.0 12.5 15.5
21.0 6.80 14.5 4.82 15.2
--
2.40 14.6 35.5 17.1 24.5 15.5 40.5
36.6 3.44 10.6 13.6
TI (p.p.m.)
228 245 208 238
298 138 275 236 217
129
1 2 4
138 180 492 268 415 312 147
130 281 311 190
Zn (p.p.m.)
Chemical analyses of pelagic sediments, Pb, Ag, Sn, T1 and Zn (reported on a carbonate-free basis) determined by emission spectrography (analyst A. Horowitz). Values for CaCOz from BOSTROMand PETERSON (1969), BOSTR6M and VALDES (1969), BOSTR6M et al. (1969); these values were determined by gas analysis and atomic absorption (% error ~< 10%).
Average area a Average area b Average area c Area average
Risepac Risepac Risepac Risepac Risepac
Group c (non-crest region)
Risepac Risepac Risepac Risepac Risepac Risepac Risepac Risepac Risepac
Group b (crest region)
Risepac Risepac Risepac Risepac
Group a (non-crest region)
Sample
LOCATION, DEPTH IN CORE, WATERDEPTH, AND CHEMICALCOMPOSITIONOF THE RISEPAC SAMPLES
TABLE I
to
O m
Z
o
N
~.] >
"0
o" >
L,1 ',D
b,~ 4~.
xD
44°58'S 54°54'S 57°49'S 55°04'S 50°02'S 60°47'S 62°52'S 59°55'S 60°02'S 58°59% 60°07'S 57°07'S 56°03'S 57°35'S 56c'53'S 56°05'S
Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt. Elt.
76°30'W 114°42'W 115°13'W 89°44'W 159°43'W 160°13'W 159°55'W 152°45'W 145°17'W 125°02'W 109°55'W 119°40'W 119°55'W 138°58'W 139°39"W 144°49'W
3,167 3,458 4,750 4,605 4,927 3,185 2,657 2,657 3,400 4,477 4,925 4,514 3,039 2,903 2,781 2,584
depth (m)
core (cm)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Water
Depth in
1 78 2 11 1 43 47 81 28 22 1 16 77 4 77 61
CaC03 (~)
79.1
25.5 25.2 26.5 48.2 46.3 86.2 343 180 8.34 17.0 25.8 37.2 91.1 135 90,3 80.0
Pb (p.p.m.)
Chemical composition
2.02
1.59 6.07 4.36 0.48 0.69 0.37 0.72 3.55 0.57 3.51 1.35
0.87
0.64 5.50 1.00 1.20
A~ (p.p.m.)
-
2.20
-
14.6 --11.7 0.97
0.54 -1.19 6.26
Sn (p.p.m.)
4.56
0.60 -0.16 1.12 0.91 2.71 17.7 20.9 0.14 0.75 1.02 0.24 0.52 26.2
TI (p.p.m.)
~ 169
167 102 57.6 162 399 140 189 365 44.2 50.2 43.3 70.2 78.1 >600 132 79.9
Zn (p.p.m.)
Chemical analyses of pelagic sediments, Pb, Ag, Sn, TI a n d Zn (reported on a carbonate-free basis) determined by emission s p e c t r o g r a p h y (analyst A. Horowitz). Values for CaCO3 from BOSTR6M a n d PETERSON (1969), BOSTR6M a n d VALDES (1969), BOSTR6M et al. (1969); these values were determined by gas analysis and atomic absorption ( % error ~< 10%).
Area average
5- 3 11- 1 11- 4 13- 1 14- 1 14- 9 14-11 14-12 14-13 14-16 15-11 15-15 15-16 15-21 15-22 15 24
Location
Sample
L O C A T I O N , D E P T H I N C O R E , W A T E R D E P T H , A N D C H E M I C A L C O M P O S I T I O N OF T H E E L T A N I N S A M P L E S
T A B L E II
4~ 4~
.~ 7" ,~
15°15'S 33 °20'S 15°31'S 13°50'S 21 °31'S 18°21'S 27 °37'S 24 °42'S 4 °24'S 5 °34'S 5 °26'S 5 °30'S 25°05'S 14°35'S 13 °53'S 13 °09'S 13°40'S 25 °26'S
M S N 48 M S N 60 D O D O 56 D O D O 77 D O D O 110 D O D O 117 D O D O 137 D O D O 141 D O D O 195 L S D A 106 L S D A 107 L S D A 108 L S D A 139 L S D A 142 L S D A 143 L S D A 144 L S D A 145 L S D H 22
81°08'E 72 °38'E 113°45'E 91°16'E 78°01'E 62 °04'E 71 °57'E 73 °05'E 84 °43'E 63 °43'E 59°15'E 57 °56'E 104°14'E 88 °02'E 90°48'E 93 °13'E 100°20'E 57 °38'E
4,996 4,224 5,377 5,480 4,610 3,398 2,955 3,600 4,092 4,090 4,010 2,550 5,215 2,630 5,320 5,226 5,986 5,105
depth (m)
core (cm)
3-23 7-21 2-15 5- 9 3-10 6--20 4-20 4-10 5-15 4-15 4-15 4-15 4-15 dredge 9-32 5-15 8-18 6-17
Water
Depth in
1 82 2 < 1 5 88 84 85 39 78 78 80 2 89 11 2 1 1
<
CaCOa (%)
79.2
42.5 106 45.1 39.5 97.4 162 98.8 192 39.0 43.6 86.9 75.8 55.4 168 28.0 51.8 40.5 52.8
Pb (p.p.m.)
Chemical composition
0.74
--
-0.22 -0.05 0.08 7.83 3.93 -0.08 ----0.63 -0.55
Ag (p.p.m.)
0.62
0.67 -1.35 -3.08 ---3.65 ---1.29 ---1.13 --
Sn (p.p.m.)
1.62
1.38 -2.93 1.50 4.20 ---2.98 2.17 --2.39 -3.52 2.27 3.31 2.62
TI (p.p.m.)
154
49.0 91.5 188 119 115 565 128 270 112 60.4 63.6 66.3 70.4 160 29.4 122 75.2 490
Zn (p.p.m.)
Chemical analyses of pelagic sediments, Pb, Ag, Sn, T1 and Z n (reported on a carbonate-free basis) determined by emission spectrography (analyst A. Horowitz). Values for CaCOa from BOSTR6M and PETERSON (1969), BOSTR~JMand VALDES (1969), and BOSTR~M et al. (1969); these values were determined by gas analysis and atomic absorption ( ~ error ~< 10%).
Area average
Location
Sample
L O C A T I O N , D E P T H IN C O R E s ~A/ATER A N D D E P T H C H E M I C A L C O M P O S I T I O N OF TIdE I N D I A N O C E A N S A M P L E S
T A B L E IIl
to 4~
N
=.
Z
©
0 Z >
> 7t ~7 N
>
"0
t-~
I
Location
19°54'N 21°57'N 35°30'N 34°51'N 34°09'N 33 °36'N 22°42'N 32°11'N 23°01'N 31 °53'N 30°22'N 30°17'N 29 °52'N 23 °30'N 29°53'N 29°42'N 29 °24'N 23 °48'N 28 °33'N 24 °16'N
P6511-29 P6303-14 P6303-15
27°43'N 24 °27'N 24°52'N
Group b (crest region)
P6303- 7 P6303- 8 P6511- 7 P6511-10 P6511-13 P6511-16 P6303- 9 P6511-17 P6303-10 P6511-18 P6511-19 P6511-20 P6511-21 P6303-I 1 P6511 -22 P6511-26 P6511-27 P6303-12 P6511-28 P6303-13
Group a (non-crest region)
Sample
m_
37°13'W 38 °29'W 40°27'W
23°02'W 26°32'W 12°55'W 13 °00'W 13 °53'W 14 °26'W 29°49'W 18 °46'W 31°20'W 20 °01"W 22 ° 0 7 ' W 23 °42'W 24 °56'W 33 °36'W 27°51'W 28°43"W 30 °20'W 35 °10'W 33 °44'W 37 °05'W 25 25 0~0
4,838 4,451 4,600
4,282 5,270 4,867 3,740 4,109 4,173 5,564 4,418 5,700 4,474 5,051 5,337 5,426 5,970 4,450 3,093 4,672 5,837 5,0|2 4,905
depth (m)
core (cm)
0-40 0-40 25 25 25 25 0--40 25 (~40 25 25 25 25 (~40 25 25 25 0-40 25 0-40
Water
Depth in
49 43 41
57 29 26 73 56 84 3 74 < 1 62 66 53 55 --~ 1 68 82 70 2 46 36
CaC03 (%)
58.8 45.9 43.1
37.5 32.2 20.9 49.6 74.9 94.4 45.8 53.8 48.3 21.0 39.7 25.2 32.7 51.5 21.1 87.7 16.7 46.9 27.3 42.1
Pb (p.p.m.)
Chemicalcomposition
L O C A T I O N , D E P T H 1N C O R E , W A T E R D E P T H A N D C H E M I C A L C O M P O S I T I O N OF T H E A T L A N T I C S A M P L E S
T A B L F IV
0.430 0.094
0.085 0.151 0.070 0.177 0.093 0.331 0.039 0.168 --0.091 0.067 -0.054 0.127 0.260 0.189 0.060 0.070 --
Ag (p.p.m.)
1.36 2.19
2.47 4.24 1.17 -5.72 5.12 2.01 3.95 2.10 2.81 2.20 2.33 1.42 1.68 2.90 6.54 4.16 3.36 1.70 1.87
(p.p.m.)
Sn
2.19 0.85 1.62
0.85 0.99 1.41 2.70 5.40 6.06 1.16 2.99 1.10 2.02 1.79 2.12 1.84 1.58 2.27 4.82 3.23 1.45 1.18 1.02
TI (p.p.m.)
58.3 68.7 87.8
25.2 124 51.6 64.4 48.2 134 61.0 69.1 64.0 24.7 65.0 31.6 38.9 65.0 28.7 85.5 15.8 105 26.6 60.1
(p.p.m.)
In
1"4
",O --0
27°08'N 25°06'N 26°15'N 29°27'N 25°37'N 25°29"N 25°5YN 26°07'N 26°13"N
24 °01 ' N 23 °21 ' N 26 °30'N 22 °30'N 26 °20'N 22 °06'N 21 °2YN 20 °36"N 26 ° 12"N 26 °00'N 25 °44'N
53 °15'W 56 °07'W 56 °08'W 59 °29'W 60 °20'W 61 °08'W 64 °04'W 67 °08'W 68 °54'W 73 °38'W 77 °07'W
40°00'W 42 °34'W 43 °30'W 44 °40'W 46 °19'W 46 °57'W 48 °31'W 51 o13'W 52 °28'W 25 25 0-40 25 0--40 25 25 25 0-40 0-40 0-40
25 0--40 25 0~A) 0-40 25 0-40 0-40 if40 6,115 6,177 5,576 5,883 5,580 5,401 5,464 5,123 5,444 5,228 2,777
4,340 4,169 2,826 3,950 4,867 4,266 4,333 5,224 5,384 < < < <
1 1 1 1 1 1 1 16 3 26 56
69 44 85 52 58 71 52 2 1 0.057 0.051 0.036 -0.132 -0.141 0.115 0.047 0.038 0.078 12-19
43.6 57.1 38.8 45.8 10-18
0.148 ---0.108 0.123 --0.051
20.2 38.3 60.3 50.5 46.0 32.6 34.6 46.1 34.5 47.6 16.4
127 23.5 106 30.8 30.9 22.7 54.3 60.7 70.2
12-20
2.81 2.17 3.33 2.24
0.98 3.10 4.45 1.70 2.07 1.39 3.36 -2.70 2.05 3.91
-2.03 -2.15 2.83 4.68 2.23 2.68 5.10
13-20
2.27 2.53 2.25 2.31
0.74 2.25 3.78 2.32 2.45 2.65 2.52 2.02 2.67 1.78 1.23
3.12 1.17 7.12 1.24 2.05 2.58 1.51 2.44 2.90
14-25
50.5 86.5 96.0 75.8
4.50 57.0 205 52.5 112 73.7 104 104 227 96.5 18.5
143 27.5 225 25.9 37.3 41.3 54.3 126 126
Chemical analyses of pelagic sediments, Pb, Ag, Sn, TI and Z n (reported on a carbonate-free basis) determined by emission spectrography (analyst A. Horowitz). Values for CaCO3 from BOSTR6M and PEa~aSON (1969), BOSTR6M and VALDES (1969), BOSTR6M et al. (1969); these values were determined by gas analysis and atomic absorption ( ~ error ~< 10~/0).
Percent error (all samples)
Average area a Average area b Average area c Area average
P6511-34 P6511-35 P6303-22 P6511-36 P6303-23 P6511-37 P6511-38 P6511-39 P6303-25 P6303-26 P6303-27
Group c (non-crest region)
P6511-30 P6303-16 P6511-31 P6303-17 P6303-18 P6511-32 P6303-19 P6303-20 P6303-21
.-O
Ix.)
7,
c)
,.q
o Z >.
z7 N
>
>
248
n. HOROWITZ
RESULTS
Tables I-IV contain the analytical results with the concentrations of Pb, Ag, Sn, T1, and Zn reported on a carbonate free basis (to remove the dilution effect of biogenous CaCO3). The biogenic contributions (tests of dead marine organisms) appear to be negligible in comparison to the elemental concentrations determined (TUREKL~N, 1965). The element/(Al + Fe + Mn) ratios have been calculated for the Eltanin samples (results not reported) because silica is a major biogenic dilutant here, in addition to CaCO3 (ANGINO, 1966). The overall concentration patterns for these samples remain essentially the same after this treatment. The results are presented in graphical form (Fig. 1-5) with concentration on a carbonate free basis plotted against distance from a ridge crest. It is assumed 200 160~
L
E
S
120 Pb(ppm} 80
40
A 0
ooOO I Pb[ppm} ~
A
..............
,' ,
RISEPAS SAMPLES
.
I 7.
:i
r
'
- Pb{ppm)
~oo
!20
ATLANTIC SAMPLES 90
Pb(ppm) 6G
30
D
~-
,
o
Fig.1. Graphical representation of Pb concentration on a carbonate free basis (C.F.B.). The solid line is the data, the dashed line is a sliding average using three samples at a time. The distance between the samples and the ridge crest was measured from a map where the sample locations were plotted and the ridge crest (central magnetic anomaly) marked. The sample distances are marked on the x-axis. In Fig.lA and B the y-axis demarks the ridge crest. In Fig.lC and D the solid vertical lines delineate the crest region and the dashed vertical line indicates the ridge crest.
Marine Geol., 9 0970) 241 259
Pb, Ag, Sn, T1 AND Zn ON ACTIVEOCEANIC RIDGES
249
Ag(ppm) 4 2 A
," % '
o ...........
-
4
~
-
:
~
.
ELTDNSN SAMPLES
Ag(pprn)
B
,
o 12
RISEPACSAMPLES
i
Aq(ppm) 8 4 - 0
40
(ppm)
D Fig.2. Graphical representation of Ag concentration on a carbonate free basis (C.F.B.). For legend see Fig.1. that the ridge crest coincides with the central magnetic anomaly as given by HEmTZLER et al. (1968). The Risepac and Atlantic samples represent single traverses and are presented in geographical position as they would appear on a map, with the ridge crest in the center. Graphs for the Eltanin and Indian Ocean samples display concentration against distance from the ridge regardless of geographical position, because they do not fall on a single traverse. The analytical errors do not change the patterns significantly. Due to the close proximity of land to some of the Indian Ocean samples, the graph for Sn is slightly misleading. The highest Sn value is from sample D O D O 195 which is extremely close to land, but also somewhat close to an active ridge. The source of the Sn appears to be terrigenous. If the traverses are broken down into crest (b group) and non-crest (a and c groups) areas, and the concentration for each area averaged, the results are more striking. The Pb, T1, and Zn values tend to be highest in the crest areas and lower in the non-crest areas. Silver (except in the Pacific and western Indian Ocean) Marine Geol., 9 (1970) 241-259
250
A.
HOROWITZ
3O
Sn(ppm)
INDIAN OCEANSAMPLES
2O
A
o
.... /
ISl
Sn(ppm)
B !
~,
RISEPACSAMPLES
ATLANTIC SAMPLES
!
120
SFl(ppm) 40
6
F
\4
Sn(ppm)
2
0
Fig.3. Graphical representation of Sn concentration on a carbonate free basis (C.F.B.). For legend see Fig.1. and especially Sn tend to show low or minimum values in the crest samples and higher values in the non-crest samples (see Table I and IV). Comparison of element concentrations from one oceanic area to another shows the concentrations for Pb, Ag, T1, and Zn are highest in the Pacific, lowest in the Atlantic, and intermediate in the Indian Ocean. The factors separating the concentrations in the Pacific from those in the Atlantic are about 1.5 times for Pb, about 3 times for Ag, about 2.7 times for T1, and about 2 times for Zn. On the other hand, Sn has the highest concentration in the Atlantic, the lowest in the Indian Ocean, and an intermediate one in the Pacific. The overall picture probably would show Sn to be lowest in the Pacific but the results are biased by one very high Sn value from sample Risepac 63 G. The concentration of Sn in the Atlantic samples is 3 times more than in the Indian Ocean samples. In order to consider the effects of sedimentation in each of these areas, the Marine Geol., 9 (1970) 241-259
Pb, Ag, Sn, T1 AND Zn ON ACTIVEOCEANICRIDGES
T I (ppm) 25
251
""N
A 30
1
Tl(ppm) I0 B
.~
o
. '~.,,--
~
.....
.. . . . . . . . . . .
" ....................
.
-
30
L~[lppm)
'i
c
ATLANTIC SAMPLES
I I
6
T~(ppm', 4
Fig.4. Graphical representation of TI concentration on a carbonate free basis (C.F.B.). For legend see Fig.1. sedimentation rates published by K u et al. (1968) were used to give more weight to samples from areas of high sedimentation and inserted in the following equation: (sedimentation rate) x (element concentration) E sedimentation rates thus producing a sedimentation rate-weighted element concentration. The values obtained may not be exact since the published sedimentation rates do not apply to the exact areas where the core samples are located. The results are given in Table V. The only variable which can be related to ridge responsibility for concentration of the elements under study, is the distance from the crest of the ridge. A series of correlation coefficients were calculated to determine the approximate effects of active ridges on element concentration (Table VI). The results indicate a negative covariation between element concentration and distance from the ridge Marine Geol., 9 (1970) 241-259
252
A. HOROWITZ
~
400 Zn(ppm)
', i A
o
-
""
LES
"'"",
-
>600ppm 600
ELTANIN SAMPLES
Zn(ppm)
,-
200 B
o
"
~
, RISEPAC SAMPLES
!
!i
6OO
I
400
C
. . . . . . . . . .
[.
~J
Zn(ppm}
24O
ISO
Zn{ppm' 120
60 0
Fig.5. Graphical representation of Zn concentration on a carbonate free basis (C.F.B.). For legend see Fig.1.
crest for Pb, Ag, TI, and Zn, i.e., higher concentrations being closer to the ridges. The amount of covariation ranges from 4 % to nearly 10 %. Correlation coefficients were determined for all combinations of Pb, Ag, Sn, TI, and Zn in order to study the associations between these elements. Correlations of the various elements with Mn and Fe were calculated to test KRAUSKOPF'S (1956) theory of hydrous oxides of Mn and Fe acting as adsorbers for trace elements, and active ridges appear to be probable sources of Fe and Mn (SKYORNYAKOVA, 1964; BOSTROMand PETERSON, 1966; etc.). Correlations were made with As because of its known volatility (ONIsHI and SANDELL, 1955; RINGWOOD, 1964; LARIMER, 1967) and because it appears to be enriched on active ridge crests (BOSTROM and VALDES, 1969); and with V because it is enriched on active ridge crests and the data were available for most of the samples (BOSTROMand PETERSON, 1969; BOSTR6M et al., 1969; BOSTRiSMand VALDES, 1969; K. Bostr6m, unpublished results, 1966-1969). Correlation coefficients were also calculated with CaCO3 to test the hypothesis that biogenic activity (tests of dead marine organisms) does not play an important role in collecting Pb, Ag, Sn, TI, and Zn. Wherever feasible, Marine Geol., 9 (1970) 241-259
Pb, Ag, Sn, T1 AND Zn ON ACTIVEOCEANICRIDGES
253
TABLE V AVERAGE ELEMENTAL CONCENTRATION (ON A CARBONATE FREE BASIS, WEIGHTED BY SEDIMENTATION RATE) FOR PORTIONS OF THE WORLD OCEANS
Area
Equatorial and southern Pacific North Atlantic Indian Ocean
Pb (p.p.m.)
Ag (p.p.m.)
Sn (p.p.m.)
TI (p.p.m.)
Zn (p.p.m.)
123 46.9 69.0
3.74 0.088 0.75
4.21 2.49 0.67
10.4 2.39 1.88
>204 74.6 125
TABLE VI CORRELATION COEFFICIENTS FOR DISTANCE VS. CONCENTRATION
Samples
Pb
Ag
Sn
TI
Zn
No. of samples
Risepac series Eltanin samples Indian Ocean samples Atlantic Ocean samples Total (all samples)
--0.058 --0.366 --0.489 --0.175 --0.291
-0.359 --0.405 --0.302 0.127 -0.297
--0.180 --0.012 0.261 0.120 0.078
--0.192 --0.354 -0.551 -0.060 -0.212
--0.181 --0.119 --0.179 0.027 --0.194
18 16 18 43 95
correlations were determined not only for the area as a whole, but also for crest (b areas) and non-crest (a and c areas) regions to see if any interelement covariations were localized in particular areas, i.e., on or off the crest. Table VII summarizes the results. Only correlation coefficients > _ 0.700 significant on the 95 ~ level or higher are shown. The value of _ 0.700 was chosen because the square of a correlation coefficient of this value will account for about 50 ~o of the covariation (CRow et al., 1960). Positive correlations for the crest areas appeared for Pb with V; T! with Zn, Mn, Fe, and V; and for Zn with T1, Mn, Fe, V, and As; negative correlations for CaCO 3 with Pb, Sn, T1, and Zn. Off the crest, positive correlations for Pb with TI, Mn, and Fe; T1 with Pb, Zn, and Mn; and for Zn with T1 and As appeared. For the areas as a whole, positive correlations were observed for Pb with TI, Mn, Fe, and V; T1 with Pb, Zn, Mn, Fe, and V; Zn with TI, Fe, and V; negative correlations were noted for CaCO 3 with Pb and Zn. The most consistent correlations (50 ~ or more of the determinations) were positive values for Pb with TI, Mn, and Fe; for TI with Pb, Zn, Mn, and Fe; and for Zn with T1, Mn, and Fe; negative values for CaCO 3 with Pb, T1, and Zn. Marine GeoL, 9 (1970) 241-259
254
A. HOROWITZ
TABLE VII STATISTICALLY
SIGNIFICANT
Sample
Pb Ag
Risepac a Risepac b Risepac c Risepac total Eltanin total Indian total Atlantic a Atlantic b Atlantic c Atlantic total
CORRELATION
COEFFICIENTS
Ag Sn
TI
Zn
Sn
Sn TI
Zn
TI
Zn
TI
Mn
Zn
Pb
**
Ag
Sn
TI
**
**
?
?
*
?
**
**
**
•
9
*
*
**
**
Zn
*
9
*
*
Blank ....... -: L 0.700 or not significant; ? == ~ 0.700 to ± 0.740; * = k 0.741 to + 0.899; ** == ~: 0.900 to -E 0.999. Symbols underlined: significant on 9 5 ~ level; all others significant on 9 9 ~ level. The letters N.D. indicate that the correlation was not calculated due to insufficient As data.
DISCUSSION The results indicate that the elements in question can be divided into two groups, the first c o n t a i n i n g Pb, TI, Zn, and sometimes Ag, and the second g r o u p c o n t a i n i n g A g a n d Sn. The distribution p a t t e r n s for Pb, T1, and Zn (except for T1 in the I n d i a n Ocean and Pb in the Risepac series) consistently show peaks in the crest regions o r areas o f high heat flow. The same p a t t e r n emerges from concentration averages for the crest (b group) a n d non-crest (a a n d c g r o u p s ) r e g i o n s . C o r r e l a t i o n coefficients for distance from the crest and c o n c e n t r a t i o n indicate a relationship between the ridges a n d the a p p e a r a n c e o f high c o n c e n t r a t i o n s o f Pb, TI, a n d Zn. These same elements also correlate well with Fe, M n , a n d V, which p r o b a b l y have a source on active oceanic ridges. Possibly Pb, TI, a n d Zn are a d d e d to deep sea sediments, to some extent, by volcanic e m a n a t i o n s from active oceanic ridges. Active ridges only affect the A g distribution in the Pacific and western I n d i a n Ocean. C o r r e l a t i o n s for distance from the crest with c o n c e n t r a t i o n s u p p o r t this view. However, A g does not correlate well with Fe, Mn, V, or As. N o n - r i d g e sources m a y account for the observed d i s t r i b u t i o n p a t t e r n s for A g in the A t l a n t i c and eastern I n d i a n Ocean. O n the o t h e r hand, Sn seems to have a purely non-ridge source in all areas studied. The d i s t r i b u t i o n p a t t e r n s and average crest and noncrest c o n c e n t r a t i o n s all tend to show low or m i n i m u m values for Sn on ridge crests. Distance vs. c o n c e n t r a t i o n correlations for Sn indicate little or no relationship between active ridges a n d the a p p e a r a n c e o f Sn. A s is the case for Ag, Sn does n o t correlate well with Fe, Mn, a n d V. Marine Geol., 9 (1970) 241-259
Pb, Ag, Sn, T1 AND Zn ON ACTIVEOCEANIC RIDGES
Fe Pb
V Ag
Sn
m
TI
? m
• * •
•
? •*
Zn
Pb
As Ag
Sn
TI
Ag
Sn
TI
Zn
*
*
**
**
**
*
**
*
?
**
**
*
*
N.D. N.D. N.D. N.D.N.D. *
N.D.
? •
Pb
• *
? **
Zn
m *
?
*
255
N.D.
N.D.
N.D.N.D.
N.D. N.D. N.D. N.D.N.D.
?
It should be pointed out that volcanic emanations from active oceanic ridges are not the only sources for Pb, Ag, TI, and Zn. The greatest concentration of these elements are derived from terrigenous sources such as continental outwash, windborn dust, glacial marine outwash, biogenous sources, cosmic sources, deposition and scavenging from sea water (including authigenic mineral formation), post-depositional alteration and migration of material buried in sediments, and submarine weathering of emplaced rocks. The ridges could probably not be expected to deliver more than 1 0 ~ of the element concentrations judging from the correlations for distance from the crest vs. element concentrations which indicated a covariation of from 4 ~o to 10 ~ . It is possible that the ridges supply Pb, Ag, Sn, T1, and Zn to pelagic sediments in all oceans but the other sources provide so much material that the ridge effects cannot be observed, as in the case of Pb in the Risepac series and T1 in the Indian Ocean. The high negative correlations of CaCO3 with Pb, T1, and Zn, and CaCO 3 with Ag in the Pacific, indicate that the concentration of these elements on active ridges probably is not due to deposition of skeletal remains. They also cast doubt on the theory that winnowing (KuENEN, 1950) is the cause of the observed concentration maxima. The bulk of CaCO3 in pelagic sediments is commonly larger than the clay size fraction and if winnowing were a factor, it would be expected that the finer clay particles would be removed while the coarser fraction remained behind. The negative correlations seem to indicate that the coarser fraction was removed, thus indicating that winnowing is not likely to have occurred, or, at least, did not cause the observed concentration maxima. Marine Geol., 9 (1970) 241-259
256
A. HOROWITZ
As a first approximation, the concentrations of Pb, Ag, Sn, Tl, and Zn listed in Table V are suggested as the oceanic sediment averages for the equatorial and southern Pacific, the Indian Ocean, and the North Atlantic. The elements that may be added to the sediments by vulcanism on active oceanic ridges all have their highest concentrations in the Pacific, with intermediate concentrations in the Indian Ocean, and lowest concentrations in the Atlantic. These differences may be a function of non-biogenic sedimentation rates which are highest in the Atlantic, intermediate in the Indian Ocean, and lowest in the Pacific, thus causing the observed differences by dilution. They cannot be a function of dilution by biogenic remains because the concentrations have been recalculated on a carbonate free basis (Table I-IV). The TI concentrations are an exception being highest in the Pacific, lowest in the Indian Ocean, and intermediate in the Atlantic. There are three possible explanations for the observed variations. The first is that the efficiency of the depositing mechanisms varies from one oceanic area to another, as observed for As (BOSTROMand VALDES, 1969) and Hg (BOSTROM and FISHER, 1969). The second is that the elements in question are brought to the surface, in part, by convection cells originating in the mantle, and are deposited on or near the crests of active ridges (this leads to the conclusion that the mantle may be inhomogeneous as far as Pb, Ag, Sn, TI, and Zn are concerned). The third can be related to HEss' (1962) theory that the active oceanic ridges are ephemeral features. If so, the quantity and composition of the material added to oceanic sediments will change as a ridge becomes older. As indicated by the concentrations of Pb, Ag, T1, and Zn, as well as the concentrations of such elements as Hg, As, Fe, Mn, etc., it appears that the East Pacific-Antarctic Ridge system is the most active, the Mid-Atlantic Ridge north of the equator is the least active, and the Indian Ocean Ridge system is of intermediate activity. The estimation of ridge activity according to elemental concentrations seems in accord with the geophysical data now available for the active ridge areas under study. The heat flow in the Pacific Ocean floor where the Risepac samples were taken is the highest, whereas that in the North Atlantic where the P6511 and P6303 samples were taken is the lowest and the Indian Ocean samples come from areas of intermediate heat flow (VON HERZEN and LANGSETH, 1965). The same correlations appear for sea-floor spreading rates. The spreading rate for the Risepac sample area is 6 cm/year, for the Eltanin sample area the average rate is 3.66 cm/ year, for the Indian Ocean the average rate is 2.03 cm/year, and for the North Atlantic the average rate is 1.33 cm/year (HEIRTZLERet al., 1968). It appears that the geochemical data for ridge derived elements mirrors the geophysical data. The higher the heat flow in a region, and the faster the spreading rate, the higher the concentration of ridge derived elements. If the activity of a ridge is the controlling factor in the ability of a ridge to add Pb, Ag, Sn, Tl, and Zn to the sediments, it could be maintained that the activity of all ridges is too low to bring Sn to the surface; the East Pacific-Antarctic Rise and the western Indian Ocean Ridge system Marine Geol., 9 (1970) 241-259
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are still sufficiently active to supply Ag contrary to the northern Mid-Atlantic Ridge which is too inactive. The northern Mid-Atlantic Ridge, in fact, appears so inactive that the Zn pattern shows almost no effect from ridge additions. The correlation coefficients calculated for Pb, Ag, Sn, T1, and Zn with Mn and Fe showed statistically significant correlations for Pb, T1, and Zn with Mn and Fe, thus lending support to the theory that these elements may be concentrated, in part, by adsorption on hydrous oxides of Mn and Fe as suggested by KRAUSKOPF (1956). Silver and Sn did not show any correlations with Mn and Fe. Co-' precipitation probably cannot explain the high correlations between Pb, TI, and Zn with Mn and Fe, as well as correlations between TI and Zn, Pb and TI, etc. because of large charge differences or incompatible ionic radii.
CONCLUSIONS
(1) The distribution of Pb, T1, and Zn is affected by processes connected with active oceanic ridges in all areas studied, while Ag distribution is affected only in the Pacific and western Indian Ocean and the distribution of Sn seems unaffected by processes on active oceanic ridges. (2) According to the concentrations of Pb, Ag, T1, and Zn, the East PacificAntarctic Ridge system is apparently the most active of the ridges studied, the Indian Ocean Ridge system is of intermediate activity, and the northern MidAtlantic Ridge is the least active. This seems to agree with the geophysical data for these areas. (3) The ridges appear to contribute no more than 10 %, and probably less, of the total concentration of Pb, Ag, TI, and Zn on active ridges. (4) Winnowing apparently has little or no effect in causing the observed concentration maxima of Pb, Ag, T1, and Zn on active ridges. (5) Lead, T1, and Zn appear to be concentrated, at least to some extent, by adsorption on hydrous oxides of Mn and Fe.
ACKNOWLEDGEMENTS
I thank Dr. Kurt Bostr~m for his advice and support throughout this research and the writing of this manuscript, and for making his samples and unpublished analytical results available. Special thanks are due to Dr. Oiva Joensuu for developing the analytical procedures used. I would also like to thank Drs. C. Emiliani, C. Harrison, J. Prospero, and S. Gartner for critically reading the manuscript and also Mr. B. Weber of the University of Miami Computing Center for running the correlation coefficients. This work was supported by National Science Foundation grants NSF GA-1356 and NSF GA-4569, the American Chemical Society PRF-#2874-A2 Marine Geol., 9 (1970) 241-259
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and the Rosenstiel School of Marine and Atmospheric Sciences for the computer programming.
T h i s s u p p o r t is g r a t e f u l l y a c k n o w l e d g e d .
REFERENCES ANGINO, E., 1966. Geochemistry of Antarctic pelagic sediments. Geochim. Cosmochim. Acta, 30: 939-961. ARRIJENItJS, G. and BONATTI, E., 1965. Neptunism and vulcanism in the ocean. In: M. SEARS (Editor), Progress in Oceanography, 3. Pergamon, London, pp.7-23. BOSTRrM, K. and FISHER, D., 1969. Distribution of mercury in East Pacific sediments. Geochim. Cosmochim. Acta, 33: 743-745. BOSTRrM, K. and PETERSON, M., 1966. Precipitates from hydrothermal exhalations on the East Pacific Rise. Econ. Geol., 61: 1258-1265. BOSTR6M, K. and PETERSON, M., 1969. The origin of aluminum-poor sediments in areas of high heat flow on the East Pacific Rise. Marine GeoL, 7: 427~147. BOSTRt3M, K. and VALDES, S., 1969. Distribution of arsenic in deep-sea sediments and rocks. Lithos, 2(4): 351-360. BOSTRrM, K., PETERSON, M., JOENSUU, O. and FISHER, D., 1969. Aluminum-poor ferromanganoan sediments on active oceanic ridges. J. Geophys. Res., 74(12): 3261-3270. CROW, E., DAVIS, F. and MAXFIELD, M., 1960. Statistics Manual. Dover Pubt., New York, N.Y., 288 pp. FISHER, D. and BOSTRrM, K., 1969. Uranium-rich sediments on the East Pacific Rise. Nature, 224(5214): 64-65. GOLDSCnMIDT, V., 1938. Geochemistry. (After his death edited by A. MUIR). Clarendon, Oxford, 730 pp. HEIRTZLER, J., DICKSON, G., HERRON, E., PITMANIII, W. and LE PlCnON, X., 1968. Marine magnetic anomalies, geomagnetic field reversals, and motions of the ocean floor and continents. J. Geophys. Res., 73(6): 2119-2135. HESS, H., 1962. History of the ocean basins. In: A. E. J. ENGEL, H. A. JAMESand B. F. LEONARD (Editors), Petrologic Studies (volume in honor of A. F. Buddington). Geol. Soc. Am., New York, N.Y., pp. 599-620. HORN, M. and ADAMS,T., 1966. Computer-derived geochemical balances and element abundances. Geochim. Cosmochim. Acta, 30: 279-297. ISACKS, B., OLIVER, J. and SYI~ES, L., 1968. Seismology and the new global tectonics. J. Geophys. Res., 73(18): 5855-5899. KRAUSKOPF, K., 1956. Factors controlling the concentration of thirteen rare metals in sea water. Geochim. Cosmochim. Acta, 9: 1-32. Ku, T., BROECKER, W. and OPDYKE, N., 1968. Comparison of sedimentation rates measured by paleomagnetic and the ionium methods of age determination. Earth Planetary Sci. Letters, 4: 1-16. KUENEN, PH., 1950. Marine Geology. Wiley, New York, N.Y., 568 pp. LARIMER, J., 1967. Chemical fractionation in meteorites, 1. Condensation of the elements. Geochim. Cosmochim. Acta, 31: 1215-1239. ONISHL H. and SANDELL, E., 1955. Geochemistry of arsenic. Geochim. Cosmochim. Acta, 7: 1-33. POLDERVAART, A., 1955. Chemistry of the earth's crust. Geol. Soc. Am., Spec. Papers, 62: l 19-144. REVELLE, R. and EMERY, K., 1951. Barite concretions from the ocean floor. Bull. Geol. Soc. Am., 62: 707-724. RINGWOOD, A., 1964. The chemical composition and origin of the earth. In: P. M. HURLEY (Editor), Advances in Earth Science. M.I.T. Press, Cambridge., Mass., pp. 287-357. RtJBEY, W., 1951. Geologic history of sea water. Bull. Geol. Soc. Am., 62:111 l-1148. SI,ZYORNYA~OVA, I., 1964. Dispersed iron and manganese in Pacific Ocean sediments, lntern. Geol. Rev., 7(12): 2161-2174. TAYLOR, S., 1964. Abundances of chemical elements in the continental crust: a new table. Geochim. Cosmochim. Acta, 28: 1273-1286.
Marine Geol., 9 (1970) 241-259
P b , A g , S n , TI AND Z n ON ACTIVE OCEANIC RIDGES
259
TUREKIAN,K., 1965. Some aspects of the geochemistry of marine sediments. In: J. RILEY and G. SKIRROW (Editors), Chemical Oceanography. Academic Press, New York, N.Y., pp. 81-126. TUREKIAN,K. and WEDEPOHL,K., 1961. Distribution of the elements in some major units of the earth's crust. Bull. Geol. Soc. 4m., 72: 175-192. VINE,F., 1966. Spreading of the ocean floor: new evidence. Science, 154: 1405. VON HERZEN,R. and LANGSETH,M., 1966. Present status of oceanic heat-flow measurements. Phys. Chem. Earth, 6: 365407. WEDEPOHL, K., 1960. Spuren-analytische Untersuchungen in Tiefseetonen aus dem Atlantik. Geochim. Cosmochim. Acta, 18: 200-231.
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