Table 1 Average compositions of normal and enriched types of basalts from mid-ocean ridges and seamounts
Normal
Enriched
Oxide wt%
Pacific
Atlantic
Galapagos
Seamounts
Pacific Picritic
Pacific Ferrobasalt
Pacific High-silica
Pacific
Atlantic
Galapagos
Seamounts
SiO 2
50.49
50.64
50.41
50.03
48.80
50.61
55.37
50.10
51.02
49.17
50.19
TiO 2
1.78
1.43
1.54
1.28
0.97
2.36
2.10
1.86
1.46
1.94
1.74
Al 2 O 3
14.55
15.17
14.75
15.97
17.12
13.30
12.92
15.69
15.36
16.86
16.71
FeO *
10.87
10.45
11.19
9.26
8.00
13.61
13.11
9.78
9.56
9.21
8.77
MnO
0.20
0.19
nd
0.15
0.14
0.23
0.21
0.19
0.18
0.15
MgO
7.22
7.53
7.49
8.06
10.28
5.92
3.64
7.00
7.31
6.93
6.80
CaO
11.58
11.62
11.69
12.21
11.93
10.43
8.05
11.17
11.54
10.90
10.67
Na 2 O
2.74
2.51
2.28
2.68
2.32
2.74
3.33
3.04
2.52
3.16
3.38
K 2 O
0.13
0.11
0.10
0.08
0.03
0.16
0.44
0.43
0.36
0.66
0.75
P 2 O 5
0.17
0.14
0.14
0.13
0.07
0.22
0.40
0.24
0.19
0.32
0.33
Sum
99.62
99.61
99.60
99.73
100
99.39
99.40
99.37
99.31
99.14
99.34
K/Ti
7.49
7.70
6.24
6.10
3.0
7.04
13.80
22.26
23.67
32.77
39.05
N ¼
2303
2148
867
623
10
706
97
304
972
65
197
Analyses done by electron microprobe on natural glasses at the Smithsonian Institution in Washington, D.C. (by W. Melson and T.O’Hearn) except the picritic samples that were analyzed at
the USGS in Denver, Co. Enriched MORB in this compilation are any that have K/Ti values greater than 13. High-silica lavas have SiO 2 values between 52 and 64.
K/Ti ¼ (K 2 O/TiO 2 ) Â 100. N ¼ number of samples used in average. FeO * ¼ total Fe as FeO.
358 MID-OCEAN RIDGE GEOCHEMISTRY AND PETROLOGY
Normal
Enriched
Oxide wt%
Pacific
Atlantic
Galapagos
Seamounts
Pacific Picritic
Pacific Ferrobasalt
Pacific High-silica
Pacific
Atlantic
Galapagos
Seamounts
SiO 2
50.49
50.64
50.41
50.03
48.80
50.61
55.37
50.10
51.02
49.17
50.19
TiO 2
1.78
1.43
1.54
1.28
0.97
2.36
2.10
1.86
1.46
1.94
1.74
Al 2 O 3
14.55
15.17
14.75
15.97
17.12
13.30
12.92
15.69
15.36
16.86
16.71
FeO *
10.87
10.45
11.19
9.26
8.00
13.61
13.11
9.78
9.56
9.21
8.77
MnO
0.20
0.19
nd
0.15
0.14
0.23
0.21
0.19
0.18
0.15
MgO
7.22
7.53
7.49
8.06
10.28
5.92
3.64
7.00
7.31
6.93
6.80
CaO
11.58
11.62
11.69
12.21
11.93
10.43
8.05
11.17
11.54
10.90
10.67
Na 2 O
2.74
2.51
2.28
2.68
2.32
2.74
3.33
3.04
2.52
3.16
3.38
K 2 O
0.13
0.11
0.10
0.08
0.03
0.16
0.44
0.43
0.36
0.66
0.75
P 2 O 5
0.17
0.14
0.14
0.13
0.07
0.22
0.40
0.24
0.19
0.32
0.33
Sum
99.62
99.61
99.60
99.73
100
99.39
99.40
99.37
99.31
99.14
99.34
K/Ti
7.49
7.70
6.24
6.10
3.0
7.04
13.80
22.26
23.67
32.77
39.05
N ¼
2303
2148
867
623
10
706
97
304
972
65
197
Analyses done by electron microprobe on natural glasses at the Smithsonian Institution in Washington, D.C. (by W. Melson and T.O’Hearn) except the picritic samples that were analyzed at
the USGS in Denver, Co. Enriched MORB in this compilation are any that have K/Ti values greater than 13. High-silica lavas have SiO 2 values between 52 and 64.
K/Ti ¼ (K 2 O/TiO 2 ) Â 100. N ¼ number of samples used in average. FeO * ¼ total Fe as FeO.
358 MID-OCEAN RIDGE GEOCHEMISTRY AND PETROLOGY