Magmatic evolution of a dying spreading axis

Evidence for the interaction of tectonics and mantle heterogeneity from the fossil Phoenix Ridge, Drake Passage

K. M. Haase*, C. Beier, S. Fretzdorff, P. T. Leat, R. A. Livermore, T. L. Barry, J. A. Pearce, F. Hauff

*Corresponding author for this work

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

New 40Ar-39Ar ages of 5.6 to 1.3Ma for lavas from the fossil Phoenix Ridge in the Drake Passage show that magmatism continued for at least 2Ma after the cessation of spreading at 3.3±0.2Ma. The Phoenix Ridge lavas are incompatible element-enriched relative to average MORB and show an increasing enrichment with decreasing age, corresponding to progressively decreasing degrees of partial melting of spinel peridotite after spreading stopped. The low-degree partial melts increasingly tap a mantle source with radiogenic Sr and Pb but unradiogenic Nd isotope ratios implying an ancient enrichment. The post-spreading magmas apparently form by buoyant ascent of enriched and easily fusible portions of the upper mantle. Only segments of fossil spreading ridges underlain by such enriched and fertile mantle show post-spreading volcanism frequently forming bathymetric highs. The Phoenix Ridge lavas belong to the Pacific, rather than the Atlantic, mantle domain in regional Sr-Nd-Pb space. Our new data show that the southern Pacific Ocean mantle is heterogeneous containing significant enriched portions that are preferentially tapped at low melt fractions. Isotopic mapping reveals that Pacific-type upper mantle flows eastward through Drake Passage and surrounds the subducting Phoenix Plate beneath the Bransfield Basin.

Original languageEnglish
Pages (from-to)115-125
Number of pages11
JournalChemical Geology
Volume280
Issue number1-2
DOIs
Publication statusPublished - 7 Jan 2011
Externally publishedYes

Keywords

  • Basalt
  • Incompatible elements
  • Mantle upwelling
  • Mid-ocean ridges
  • Partial melting

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