Lead isotope evidence for young trace element enrichment in the oceanic upper mantle

Details Lead isotope evidence for young trace element enrichment in the oceanic upper mantle Lead isotope evidence for young trace element enrichment in the oceanic upper mantle

Oct 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992natur.359..623h&link_type=abstract

Nature (ISSN 0028-0836), vol. 359, no. 6396, p. 623-627.

Computer Science

20

Basalt, Earth Mantle, Lead Isotopes, Lithosphere, Ocean Bottom, Trace Elements, Geochemistry, Mid-Ocean Ridges, Neodymium Isotopes, Strontium Isotopes

Scientific paper

A recent study of Cameroon line lavas indicated large in situ fractionations of U and Th relative to Pb in the upper mantle about 10 exp 8 yrs ago. Nd, Sr, and Pb isotope data for a variety of central Atlantic islands are presented, and it is shown that similar offsets in Pb isotope ratios are found in lavas from the islands of Madeira and Trinidade. Like the Cameroon lavas, these lavas are characterized by high U/Pb and Ce/Pb, low K/U, and are located in areas of old oceanic lithosphere. But in contrast to the Cameroon line, the Madeira lavas are derived from an enriched MORB-type source with low Pb-207/Pb-204 and Sr-87/Sr-86 and high Nd-143/Nd-144. The Pb isotope data can be explained if the U/Pb ratios in the sources are comparable to those observed for the lavas and the U/Pb fractionation occurred at the time of formation of the local oceanic lithosphere. The U/Pb fractionation must have occurred at shallow depths in the mantle near a spreading ridge and the resulting enriched source regions have since remained fixed relative to the migrating lithosphere.

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