Geochemistry of Fe-Mn crusts in sediments of the Central Indian Ridge
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| Natura: | Dataset Open Access |
| Lingua: | en |
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PANGAEA
1998
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| _version_ | 1867170456865341440 |
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| author | Kuhn, Thomas Bau, Michael Blum, Nevin Halbach, Peter |
| author_facet | Kuhn, Thomas Bau, Michael Blum, Nevin Halbach, Peter |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | Layered Fe-Mn crusts from the off-axis region of the first segment of the Central Indian Ridge north of the Rodrigues Triple Junction were studied geochemically and mineralogically. Vernadite (delta-MnO2) is the main mineral oxide phase. 230Thxs and Co concentrations suggest high growth rates of up to 29 mm/Myr and a maximum age of the basal crust layer of 1 Ma. Whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation, Co, Pb, Ni and Ti concentrations are strikingly lower. Concentrations and distribution of the strictly trivalent rare-earths and yttrium (REY) are typical of hydrogenetic ferromanganese oxide precipitates, but in marked contrast, the crusts are characterized by negative CeSN (shale normalized) anomalies and (Ce/Pr)SN ratios less than unity. Profiles through the crusts reveal only minor variations of the REY distribution and (Ce/Pr)SN ratios range from 0.45 to 0.68 (compared to ratios of up to 2 for typical hydrogenetic crusts from the Central Indian Basin). The apparent bulk partition coefficients between the crusts and seawater suggest that for the strictly trivalent REY the adsorption-desorption equilibrium has been reached. Positive Ce anomalies in the partition coefficient patterns reveal preferential uptake of Ce, but to a lesser extent than in normal hydrogenetic crusts. A new parameter (excess Ce, Cexs) to quantify the degree of decoupling of Ce from REY(III) is established on the basis of partition coefficients. Cexs/Cebulk ratios suggest that the CIR crusts formed by precipitation of Fe-Mn oxides from a hydrothermal plume and that in hydrothermal plumes and normal seawater the enrichment of Ce results from the same oxidative sorption process. The growth rates, calculated with 230Thxs data as well as with the Co formula, are inversely related to Cexs. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_735050 |
| institution | PANGAEA |
| language | en |
| publishDate | 1998 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | Geochemistry of Fe-Mn crusts in sediments of the Central Indian Ridge Kuhn, Thomas Bau, Michael Blum, Nevin Halbach, Peter BCR; Box corer (Reineck); HYDROTRUNC; KL; PC; Piston corer; Piston corer (BGR type); Rodriguez Triple Junction; SO92; SO92_26PC; SO92_27PC; SO92_31GTV; SO92_36GTV; SO92_38GK; SO92_54GK; SO92_55KL; SO92_58KL; SO92_60GTV; SO92_60GTV/13; SO92_60GTV/15; SO92_72PC; SO92_74GTV; SO92_81PC; SO92_95PC; Sonne; Television-Grab; TVG Layered Fe-Mn crusts from the off-axis region of the first segment of the Central Indian Ridge north of the Rodrigues Triple Junction were studied geochemically and mineralogically. Vernadite (delta-MnO2) is the main mineral oxide phase. 230Thxs and Co concentrations suggest high growth rates of up to 29 mm/Myr and a maximum age of the basal crust layer of 1 Ma. Whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation, Co, Pb, Ni and Ti concentrations are strikingly lower. Concentrations and distribution of the strictly trivalent rare-earths and yttrium (REY) are typical of hydrogenetic ferromanganese oxide precipitates, but in marked contrast, the crusts are characterized by negative CeSN (shale normalized) anomalies and (Ce/Pr)SN ratios less than unity. Profiles through the crusts reveal only minor variations of the REY distribution and (Ce/Pr)SN ratios range from 0.45 to 0.68 (compared to ratios of up to 2 for typical hydrogenetic crusts from the Central Indian Basin). The apparent bulk partition coefficients between the crusts and seawater suggest that for the strictly trivalent REY the adsorption-desorption equilibrium has been reached. Positive Ce anomalies in the partition coefficient patterns reveal preferential uptake of Ce, but to a lesser extent than in normal hydrogenetic crusts. A new parameter (excess Ce, Cexs) to quantify the degree of decoupling of Ce from REY(III) is established on the basis of partition coefficients. Cexs/Cebulk ratios suggest that the CIR crusts formed by precipitation of Fe-Mn oxides from a hydrothermal plume and that in hydrothermal plumes and normal seawater the enrichment of Ce results from the same oxidative sorption process. The growth rates, calculated with 230Thxs data as well as with the Co formula, are inversely related to Cexs. |
| title | Geochemistry of Fe-Mn crusts in sediments of the Central Indian Ridge |
| topic | BCR; Box corer (Reineck); HYDROTRUNC; KL; PC; Piston corer; Piston corer (BGR type); Rodriguez Triple Junction; SO92; SO92_26PC; SO92_27PC; SO92_31GTV; SO92_36GTV; SO92_38GK; SO92_54GK; SO92_55KL; SO92_58KL; SO92_60GTV; SO92_60GTV/13; SO92_60GTV/15; SO92_72PC; SO92_74GTV; SO92_81PC; SO92_95PC; Sonne; Television-Grab; TVG |
| url | https://doi.org/10.1594/PANGAEA.735050 |