Sr and Nd isotopic variations in ferromanganese crusts from the Central Pacific: Implications for age and source provenance

Journal Article · Thu Sep 01 00:00:00 EDT 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90125-1· OSTI ID:5221420

Futa, Kiyoto; Peterman, Z E ^[1]; Hein, J R ^[2]

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1. Geological Survey, Denver, CO (USA)
2. Geological Survey, Menlo Park, CA (USA)

Isotopic analyses of two hydrogenetic ferromanganese (Fe-Mn) crusts from volcanic edifices in the central Pacific Ocean reveal systematic variations in {sup 87}Sr/{sup 86}Sr and {sup 143}Nd/{sup 144}Nd, with both ratios decreasing as a function of depth into the Fe-Mn crusts. Leaching experiments suggest that Sr in the crusts is contained in at least two discrete sites. A loosely bound Sr, dominated by modern marine Sr, is removed by leaching with a 10 percent acetic acid solution. The {sup 87}Sr/{sup 86}Sr ratio of the residue is significantly less than the {sup 87}Sr/{sup 86}Sr ratio of the unleached material. The Sr-isotope ratios of leached samples are compared with the temporal variation in seawater to provide ages for layers within the Fe-Mn crusts. These data suggest that the oldest crust layers began to accrete in the early to middle Miocene. Correlated to the {sup 87}Sr/{sup 86}Sr variations, {sup 143}Nd/{sup 144}Nd ratios suggest that the Nd-isotope composition of central Pacific Ocean seawater also changed systematically over this time interval, or that the Fe-Mn crusts simply incorporated Nd from various parts of an isotopically heterogeneous ocean as the crusts were carried along with the oceanic plate. In contrast to the layered ferromanganese crust, the phosphatized volcaniclastic substrates have Sr and Nd isotope compositions that are consistent with their volcanic origin.

• OSTI ID: 5221420
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 52:9; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
OCEANIC CRUST
VOLCANIC ROCKS
PACIFIC OCEAN
CHEMICAL COMPOSITION
ISOTOPE DATING
PETROGENESIS
GEOCHEMISTRY
IRON COMPOUNDS
ISOTOPE RATIO
MANGANESE COMPOUNDS
NEODYMIUM 143
NEODYMIUM 144
SEAWATER
STRONTIUM 86
STRONTIUM 87
AGE ESTIMATION
ALKALINE EARTH ISOTOPES
ALPHA DECAY RADIOISOTOPES
BETA DECAY RADIOISOTOPES
CHEMISTRY
EARTH CRUST
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HOURS LIVING RADIOISOTOPES
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
NEODYMIUM ISOTOPES
NUCLEI
OXYGEN COMPOUNDS
RADIOISOTOPES
RARE EARTH NUCLEI
ROCKS
SEAS
STABLE ISOTOPES
STRONTIUM ISOTOPES
SURFACE WATERS
TRANSITION ELEMENT COMPOUNDS
WATER
YEARS LIVING RADIOISOTOPES
580000* - Geosciences