Deep Sea Minerals - Vol 2 - Manganese Nodules
Formation environment for manganese nodules
Hydrogenetic nodules
4000
Hydro- and diagenetic nodules
Water depth in metres
Porous sediment Consolidated sediment Basalt
Diagenetic nodules
6500
Accretion of colloidal manganese from seawater
Migration of Mn 2+ ions and other cations from seawater into pore water for diagenetic formation of nodules
Source: Modified from Koschinsky, Jocobs University, Bremen
Figure 3. Formation of manganese nodules. This process takes place in water depths of 4 000 to 6 500 metres.
Hydrogenetic nodules grow extremely slowly, at a rate of about 1 to 10 mm per million years, while diagenetic nodules grow at rates of several hundred mm per million years. Most nodules
form by both hydrogenetic and diagenetic precipitation and, therefore, grow at intermediate rates of several tens of mm per million years (Figure 4).
Cumulative nodule growth rate l ti n l gr t r t
Nodule growth rate from core to rim o ule gro th rate fro core to rim
Milimetre/million year il metre/million year
Milimetre/million year Milimetre/mill on year
Growth rate as measured Growth rate as measured
Growth rate as measured Growth rate as measured
20
20
20
20
Core
Core
15
15
15
15
Core
Core
10
10
10
10
Rim
Rim
5
5
5
5
Rim
Rim
0
0
0
0
0
0
2
2
4
4
6
6
8
8
10
10
12
12
0
0
2
2
4
4
6
6
8
8
10
10
12
12
Growth age in million years Growth age in million years
Mill on years
Million years
Figure 4. Growth age and growth rate of nodules. Growth age versus cumulative growth rate (left) and growth rate versus model age (right) in nodules from the Campbell Nodule Field, New Zealand. Extrapolated ages are based on measured 10Be/9Be ratios and the extrapolated 10Be/9Be ratio of the rim. (ii) Model Ages are based on measured 10Be/9Be ratios and an assumed initial 10Be/9Be ratio. (iii) Growth Ages (in m.y.) are based on the elapsed time from initiation of growth (i.e., core to rim). Graham et al. 2004.
MANGANESE NODULES 9
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