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Paleobathymetry of the crest of spreading ridges related to the age of ocean basins — comment
454
Earth and Planetary Science Letters, 35 (1977) 454-456 © Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
[4]
PALEOBATHYMETRY OF THE CREST OF SPREADING RIDGES RELATED TO THE AGE OF OCEAN BASINS - COMMENT
PETER A. RONA NOAA - Atlantic Oceanographic and Meteorological Laboratories, Miami, Fla. (USA)
Received April 7, 1977
J.J. Veever's paper [1] and prior work based on the age-depth relation of oceanic crust [ 2 - 4 ] treat the mean crestal depth of oceanic ridges. In treating the depth of an oceanic ridge simply as variation about a mean, they overlook a systematic variation in depth that exists along the axes of oceanic ridges. Crestal depth along the axis of an oceanic ridge varies as a function of geographic latitude, generally increasing from the pole to the equator of rotation of the lithospheric plates bounding the oceanic ridge [5]. When this systematic variation in crestal depth along the axes of oceanic ridges was noted [5], it was unclear whether the depth variation was related to pole of plate rotation or geographic pole, because the present poles of plate rotation tend to lie close to the geographic poles (Table 1). Menard and Dorman [6] have recently shown that the depth variation is related to geographic latitude. For example, the crestal depth of the Mid-Atlantic Ridge increases as the cosine of the latitude from about 1 km below sea level at 60°N to 3 kin below sea level at 10°N (Fig. 1); the depth of the ridge crest is irregular in an equatorial transition zone between about 10°N and 5°S; the depth of the ridge crest then decreases from about 3 kin below sea level at 5°S to 2 km below sea level at 52°S (Table 1). A compilation of crestal depths along the axes of other oceanic ridges (Table 1) based on the data of Anderson et al. [4], indicates that a latitude-depth relation also holds for the Southwest Indian Ridge, the Cadsberg-Central Indian Ridge, a segment of the Southeast Indian Ridge (segment 1 in Table 1), the Pacific-Antarctic Ridge, and a segment of the East Pacific Rise (segment 4 in Table 1).
Exceptions to the depth-latitude relation include segments of the Southeast Indian Ridge (segments 2, 3, in Table 1), and of the East Pacific Rise (segments l, 2, 3, in Table 1). The latitude-depth relation, the systematic increase in crestal depth of oceanic ridges toward the equator, is obviously independent of the age-depth relation, because age is supposed to be the same along the axis of a given oceanic ridge. The latitude-depth relation appears to be maintained as oceanic crust subsides about an oceanic ridge according to the agedepth relation. For example, the inclination of the axes of maximum depth of the eastern and western basins of the North Atlantic and of the axis of the crest of the Mid-Atlantic Ridge are sub-parallel (Fig. 1) [5], evidencing the independent and simultaneous operation of the latitude-depth and age-depth relations. The observation of the systematic variation of crestal depth, along the axes of oceanic ridges does not conflict with the work of Veevers [1] and others [ 2 - 4 ] based on the age-depth relation, but indicates that processes other than thermal contraction of the lithosphere as a function of age are required to explain the latitude-depth relation [6], as well as exceptions to that relation.
References
1 J.J. Veevers, Paleobathymetry of the crest of spreading ridges related to the age of ocean basins, Earth Planet. Sc£ Lett. 34 (1977) 100-106. 2 H.W. Menard, Elevation and subsidence of oceanic crust, Earth Planet. Sci. Lett. 6 (1969) 275-284.
69°S 69°S 69°S 57 ° N 57°N 41°N
PA/AN
PA/AN PA/AN
(.ORr.)
• ATITUC)'~
48"
'46"
42"
40"
3~"
34"
32 e
~
'
30"
~
65°S-60°S 60°S-33°S 33 ° S-23 ° S 20°S-2°N 2°N-20°N
60°S-62°S
50°S-60°S
49°S-50°S
25°S-49°S
10°N-25°S
51°S-25°S
52°S-51°S
60°N-39°N 39°N-10°N 10° N-5 ° S 5°S-52°S
EAST AXIS - - ~ 3~"
100°E 100°E 86°W 86°W 108°W
100°E
32°E
32°E
32°E
45°E
13°W
13°W
128°E 23°E 37°W 37°W
long.
Latitude span
"
21 •
-
~ ~e
24 •
DEPTH AT iNNER MARGIN O F HIGH FRACTUIED PLATEAU
170°E-150°W 150°W-l12°W 112°W - 114°W 114°W-102°W 102°W-105°W
155°E-168°E
140°E-150°E
110°E-140°E
70°E-110°E
57°E-70°E
30°E-70°E
5°E-30°E
30°W-30°W 30°W-40°W 40°W - 12°W 12°W-5°E
Longitude span
2~"
ao*
* 'l8" i
2.0-2.8 2.8-2.8 2.8-2.8 2.9-2.9 2.9-2.7
2.0-2.0
irregular
3.0-2.5
2.8-3.0
2.5-2.8
2.2-2.8
2.0-2.2
1.0-1.8 1.8-3.0 irregular 3.0-2.0
Depth change [4] (km)
IQe
,4-
* 1 6000
I000
O
,:~e~ 7000
northeast horizontal horizontal horizontal south
horizontal
irregular
west
southeast
south
northeast
east
south south irregular north
Direction of deepening of oceanic ridge crest
Fig. 1. Curves through data points along the axis of the crest of the Mid-Atlantic Ridge (dashed line) and along the axes of maximum depth of the eastern and western basins (solid lines) of the North Atlantic [5 ].
50"
54"
52"
AXISwEsTOFANDMAXIMUMEB AA sT S,NsORPT,N H
?QO0
R-, R-2
6000
5OOO
3000
2OOO
IO00
NZ/PA CO/PA
NZ/PA
44"
ll°N
IN/AN
L
1 I°N
IN/AN
R-6
li°N
IN/AN
~
19°N
IN/AF
~
19°S
AF/AN
0
19°S
AF/AN
AF/SAM
AF/SAM
69°N 80°N 57 ° N 57°N
EU/NAM AF/NAM
Mid-Atlantic Ridge 1 Mid-Atlantic Ridge 2 Mid-Atlantic Ridge 3 Mid-Atlantic Ridge 4 Southwest Indian Ridge 1 Southwest Indian Ridge 2 Carlsberg-Central Indian Ridge Southeast Indian Ridge 1 Southeast Indian Ridge 2 Southeast Indian Ridge 3 Pacific-Antarctic Ridge 1 Pacific-Antarctic Ridge 2 East Pacific Rise 1 East Pacific Rise 2 East Pacific Rise 3 East Pacific Rise 4
lat.
Pole of plate rotation [7]
Bounding plates [7]
Oceanic ridge
Variation in crestal depth of oceanic ridges with geographic and plate parameters
TABLE 1
ol (31
456 3 J.G. Sclater, R.N. Anderson and M.L. Bell, Elevation of ridges and evolution of the Central Eastern Pacific, J. Geophys. Res. 76 (1971) 7888-7915. 4 R.N. Anderson, D. McKenzie and J.G. Sclater, Gravity, bathymetry and convection in the earth, Earth Planet. ScL Lett. 18 (1973) 391-407. 5 P.A. Rona, Depth distribution in ocean basins and plate tectonics, Nature 231 (1971) 179-180.
6 H.W. Menard and L.M. Dorman, On the variation of ocean depth with latitude, EOS, Trans. Am. Geophys. Union 57 (1976) 933. 7 J.B. Minster, T.H. Jordan, P. Molnar and E. Haines, Numerical modelling of instantaneous plate tectonics, Geophys. J.R. Astron. Soc. 36 (1974) 541-576.
Earth and Planetary Science Letters, 35 (1977) 454-456 © Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
[4]
PALEOBATHYMETRY OF THE CREST OF SPREADING RIDGES RELATED TO THE AGE OF OCEAN BASINS - COMMENT
PETER A. RONA NOAA - Atlantic Oceanographic and Meteorological Laboratories, Miami, Fla. (USA)
Received April 7, 1977
J.J. Veever's paper [1] and prior work based on the age-depth relation of oceanic crust [ 2 - 4 ] treat the mean crestal depth of oceanic ridges. In treating the depth of an oceanic ridge simply as variation about a mean, they overlook a systematic variation in depth that exists along the axes of oceanic ridges. Crestal depth along the axis of an oceanic ridge varies as a function of geographic latitude, generally increasing from the pole to the equator of rotation of the lithospheric plates bounding the oceanic ridge [5]. When this systematic variation in crestal depth along the axes of oceanic ridges was noted [5], it was unclear whether the depth variation was related to pole of plate rotation or geographic pole, because the present poles of plate rotation tend to lie close to the geographic poles (Table 1). Menard and Dorman [6] have recently shown that the depth variation is related to geographic latitude. For example, the crestal depth of the Mid-Atlantic Ridge increases as the cosine of the latitude from about 1 km below sea level at 60°N to 3 kin below sea level at 10°N (Fig. 1); the depth of the ridge crest is irregular in an equatorial transition zone between about 10°N and 5°S; the depth of the ridge crest then decreases from about 3 kin below sea level at 5°S to 2 km below sea level at 52°S (Table 1). A compilation of crestal depths along the axes of other oceanic ridges (Table 1) based on the data of Anderson et al. [4], indicates that a latitude-depth relation also holds for the Southwest Indian Ridge, the Cadsberg-Central Indian Ridge, a segment of the Southeast Indian Ridge (segment 1 in Table 1), the Pacific-Antarctic Ridge, and a segment of the East Pacific Rise (segment 4 in Table 1).
Exceptions to the depth-latitude relation include segments of the Southeast Indian Ridge (segments 2, 3, in Table 1), and of the East Pacific Rise (segments l, 2, 3, in Table 1). The latitude-depth relation, the systematic increase in crestal depth of oceanic ridges toward the equator, is obviously independent of the age-depth relation, because age is supposed to be the same along the axis of a given oceanic ridge. The latitude-depth relation appears to be maintained as oceanic crust subsides about an oceanic ridge according to the agedepth relation. For example, the inclination of the axes of maximum depth of the eastern and western basins of the North Atlantic and of the axis of the crest of the Mid-Atlantic Ridge are sub-parallel (Fig. 1) [5], evidencing the independent and simultaneous operation of the latitude-depth and age-depth relations. The observation of the systematic variation of crestal depth, along the axes of oceanic ridges does not conflict with the work of Veevers [1] and others [ 2 - 4 ] based on the age-depth relation, but indicates that processes other than thermal contraction of the lithosphere as a function of age are required to explain the latitude-depth relation [6], as well as exceptions to that relation.
References
1 J.J. Veevers, Paleobathymetry of the crest of spreading ridges related to the age of ocean basins, Earth Planet. Sc£ Lett. 34 (1977) 100-106. 2 H.W. Menard, Elevation and subsidence of oceanic crust, Earth Planet. Sci. Lett. 6 (1969) 275-284.
69°S 69°S 69°S 57 ° N 57°N 41°N
PA/AN
PA/AN PA/AN
(.ORr.)
• ATITUC)'~
48"
'46"
42"
40"
3~"
34"
32 e
~
'
30"
~
65°S-60°S 60°S-33°S 33 ° S-23 ° S 20°S-2°N 2°N-20°N
60°S-62°S
50°S-60°S
49°S-50°S
25°S-49°S
10°N-25°S
51°S-25°S
52°S-51°S
60°N-39°N 39°N-10°N 10° N-5 ° S 5°S-52°S
EAST AXIS - - ~ 3~"
100°E 100°E 86°W 86°W 108°W
100°E
32°E
32°E
32°E
45°E
13°W
13°W
128°E 23°E 37°W 37°W
long.
Latitude span
"
21 •
-
~ ~e
24 •
DEPTH AT iNNER MARGIN O F HIGH FRACTUIED PLATEAU
170°E-150°W 150°W-l12°W 112°W - 114°W 114°W-102°W 102°W-105°W
155°E-168°E
140°E-150°E
110°E-140°E
70°E-110°E
57°E-70°E
30°E-70°E
5°E-30°E
30°W-30°W 30°W-40°W 40°W - 12°W 12°W-5°E
Longitude span
2~"
ao*
* 'l8" i
2.0-2.8 2.8-2.8 2.8-2.8 2.9-2.9 2.9-2.7
2.0-2.0
irregular
3.0-2.5
2.8-3.0
2.5-2.8
2.2-2.8
2.0-2.2
1.0-1.8 1.8-3.0 irregular 3.0-2.0
Depth change [4] (km)
IQe
,4-
* 1 6000
I000
O
,:~e~ 7000
northeast horizontal horizontal horizontal south
horizontal
irregular
west
southeast
south
northeast
east
south south irregular north
Direction of deepening of oceanic ridge crest
Fig. 1. Curves through data points along the axis of the crest of the Mid-Atlantic Ridge (dashed line) and along the axes of maximum depth of the eastern and western basins (solid lines) of the North Atlantic [5 ].
50"
54"
52"
AXISwEsTOFANDMAXIMUMEB AA sT S,NsORPT,N H
?QO0
R-, R-2
6000
5OOO
3000
2OOO
IO00
NZ/PA CO/PA
NZ/PA
44"
ll°N
IN/AN
L
1 I°N
IN/AN
R-6
li°N
IN/AN
~
19°N
IN/AF
~
19°S
AF/AN
0
19°S
AF/AN
AF/SAM
AF/SAM
69°N 80°N 57 ° N 57°N
EU/NAM AF/NAM
Mid-Atlantic Ridge 1 Mid-Atlantic Ridge 2 Mid-Atlantic Ridge 3 Mid-Atlantic Ridge 4 Southwest Indian Ridge 1 Southwest Indian Ridge 2 Carlsberg-Central Indian Ridge Southeast Indian Ridge 1 Southeast Indian Ridge 2 Southeast Indian Ridge 3 Pacific-Antarctic Ridge 1 Pacific-Antarctic Ridge 2 East Pacific Rise 1 East Pacific Rise 2 East Pacific Rise 3 East Pacific Rise 4
lat.
Pole of plate rotation [7]
Bounding plates [7]
Oceanic ridge
Variation in crestal depth of oceanic ridges with geographic and plate parameters
TABLE 1
ol (31
456 3 J.G. Sclater, R.N. Anderson and M.L. Bell, Elevation of ridges and evolution of the Central Eastern Pacific, J. Geophys. Res. 76 (1971) 7888-7915. 4 R.N. Anderson, D. McKenzie and J.G. Sclater, Gravity, bathymetry and convection in the earth, Earth Planet. ScL Lett. 18 (1973) 391-407. 5 P.A. Rona, Depth distribution in ocean basins and plate tectonics, Nature 231 (1971) 179-180.
6 H.W. Menard and L.M. Dorman, On the variation of ocean depth with latitude, EOS, Trans. Am. Geophys. Union 57 (1976) 933. 7 J.B. Minster, T.H. Jordan, P. Molnar and E. Haines, Numerical modelling of instantaneous plate tectonics, Geophys. J.R. Astron. Soc. 36 (1974) 541-576.