Copper-nickel-rich, amalgamated ferromanganese crust-nodule deposits from Shatsky Rise, NW Pacific

Hein, J. R., Conrad, T. A., Frank, Martin, Christl, M. and Sager, W. W. (2012) Copper-nickel-rich, amalgamated ferromanganese crust-nodule deposits from Shatsky Rise, NW Pacific Geochemistry Geophysics Geosystems, 13 (10). Q10022. DOI 10.1029/2012GC004286.

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A unique set of ferromanganese crusts and nodules collected from Shatsky Rise (SR), NW Pacific, were analyzed for mineralogical and chemical compositions, and dated using Be isotopes and cobalt chronometry. The composition of these midlatitude, deep-water deposits is markedly different from northwest-equatorial Pacific (PCZ) crusts, where most studies have been conducted. Crusts and nodules on SR formed in close proximity and some nodule deposits were cemented and overgrown by crusts, forming amalgamated deposits. The deep-water SR crusts are high in Cu, Li, and Th and low in Co, Te, and Tl concentrations compared to PCZ crusts. Thorium concentrations (ppm) are especially striking with a high of 152 (mean 56), compared to PCZ crusts (mean 11). The deep-water SR crusts show a diagenetic chemical signal, but not a diagenetic mineralogy, which together constrain the redox conditions to early oxic diagenesis. Diagenetic input to crusts is rare, but unequivocal in these deep-water crusts. Copper, Ni, and Li are strongly enriched in SR deep-water deposits, but only in layers older than about 3.4 Ma. Diagenetic reactions in the sediment and dissolution of biogenic calcite in the water column are the likely sources of these metals. The highest concentrations of Li are in crust layers that formed near the calcite compensation depth. The onset of Ni, Cu, and Li enrichment in the middle Miocene and cessation at about 3.4 Ma were accompanied by changes in the deep-water environment, especially composition and flow rates of water masses, and location of the carbonate compensation depth.

Key Points
- Fe-Mn crusts can have a diagenetic component
- Mid-latitude N. Pacific deep-water Fe-Mn crusts are uniquely enriched in Cu, Th, Li
- Temporal changes in deep-ocean geochemical processes are recorded

Document Type: Article
Additional Information: WOS:000310690700005
Keywords: Palaeoceanography; age dating; deep-water; diagenetic crusts; ferromanganese crusts and nodules; biogeosciences: metals; marine geochemistry; geochemistry: major and trace element geochemistry; POLAR WANDER PATH; COBALT-RICH; DEEP-SEA; ELEMENTAL COMPOSITION; CHEMICAL-COMPOSITION; TRIPLE JUNCTION; SUBSTRATE ROCKS; SOUTH-PACIFIC; EAST PACIFIC; TRACE-METALS
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
DOI etc.: 10.1029/2012GC004286
ISSN: 1525-2027
Date Deposited: 29 Nov 2012 14:28
Last Modified: 28 Jul 2017 08:31

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