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

Geochimica et Cosmochimica Acta

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Abstract

Isotopic analyses of two hydrogenetic ferromanganese (Fe-Mn) crusts from volcanic edifices in the central Pacific Ocean reveal systematic variations in 87Sr 86Sr and 143Nd 144Nd, 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 87Sr 86Sr ratio of the residue is significantly less than the 87Sr 86Sr 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 87Sr 86Sr variations, 143Nd 144Nd 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 isotopieally 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. ?? 1988.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Sr and Nd isotopic variations in ferromanganese crusts from the Central Pacific: Implications for age and source provenance
Series title:
Geochimica et Cosmochimica Acta
Volume
52
Issue:
9
Year Published:
1988
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geochimica et Cosmochimica Acta
First page:
2229
Last page:
2233