Sr, Nd and Pb isotopic variation along the Pacific-Antarctic risecrest, 53-57°S: Implications for the composition and dynamics of the South Pacific upper mantle

Details Sr, Nd and Pb isotopic variation along the Pacific-Antarctic risecrest, 53-57°S: Implications for the composition and dynamics of the South Pacific upper mantle Sr, Nd and Pb isotopic variation along the Pacific-Antarctic risecrest, 53-57°S: Implications for the composition and dynamics of the South Pacific upper mantle

Jan 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998e%26psl.154..109c&link_type=abstract

Earth and Planetary Science Letters, vol. 154, Issue 1-4, pp.109-125

Computer Science

20

Sr-87/Sr-86, Nd-144/Nd-143, Pb-208/Pb-204, Isotope Ratios, Petrology, Mid-Ocean Ridge Basalts, Pacific-Antarctic Ridge, East Pacific Rise, South Pacific

Scientific paper

Sr, Nd and Pb isotope data for basalts from spreading axes and off-axis volcanoes near the Pacific-Antarctic risecrest, from Vacquier transform to just south of Udintsev transform, reveal an isotopically heterogeneous upper mantle. The isotopic composition of the mantle is represented by three end-members: (1) the `depleted' source of the bulk of Pacific normal-type mid-ocean ridge basalts (N-MORB); (2) an `enriched' source that produces basalts of the Hollister Ridge; and (3) a source, restricted to two adjacent sample locales, similar to that of Indian MORB. The distribution of these isotopic heterogeneities along the Pacific-Antarctic risecrest suggests two alternative hypotheses on the nature and dynamics of the south Pacific upper mantle. The whole area could be a single N-MORB mantle domain that shows a weak but continuous increase in 143 Nd/ 144 Nd from northeast to southwest across more than 2000 km of sea floor. The gradient is unrelated to the Louisville hotspot because Louisville basalts have low 143 Nd/ 144 Nd and the hotspot's influence along the ridge is spatially limited and near the high 143 Nd/ 144 Nd southwestern end of the gradient. The gradient appears consistent with a southwestward flow of the Pacific N-MORB-type mantle that has been proposed mainly on the basis of ridge morphology. That the N-MORB mantle domain is continuous across Heezen suggests that large-scale magmatic segmentation is not related to the largest structural offsets of the Pacific ridges. Alternatively, the higher 87 Sr/ 86 Sr, Nd and 8/4 of samples from southwest of the Heezen transform relative to those from the northeast could result from southwestward pumping of both plume and Indian Ocean-type mantle material by the Louisville hotspot. The Heezen transform forms a prominent tectonic and mantle domain boundary that prohibits the Louisville- and Indian Ocean-type mantle from flowing towards and contaminating the depleted Pacific-type source in the northeast.

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