Abstract:
The Canary Island primitive basaltic magmas 31 are thought to be derived from a
HIMU-type upwelling mantle containing isotopically depleted (NMORB) component and
having interacted with an enriched (EM)-type component whose origin is still a subject of
debate. We have studied the relationships between Ni, Mn and Ca concentrations in olivine
phenocrysts (85.6-90.0 mol.% Fo, 1722-3915 ppm Ni, 1085-1552 ppm Mn, 1222-3002 ppm
Ca) from the most primitive subaerial and ODP Leg 157 high-silica (picritic to olivine
basaltic) lavas with their bulk rock Sr-Nd-Pb isotope compositions (87Sr/86Sr = 0.70315-
0.70331, 143Nd/144Nd = 0.51288-0.51292, 206Pb/204Pb = 19.55-19.93, 207Pb/204Pb = 15.60-
15.63, 208Pb/204Pb = 39.31-39.69). Our data point toward the presence of both a peridotitic and
a pyroxenitic component in the magma source. Using the model [Sobolev et al. (2007) The
amount of recycled crust in sources of mantle-derived melts. Science 316: 412-417] in which
the reaction of Si-rich melts originated during partial melting of eclogite (a high pressure
product of subducted oceanic crust) with ambient peridotitic mantle forms olivine-free
reaction pyroxenite, we obtain an endmember composition for peridotite with 87Sr/86Sr =
0.70337, 143Nd/144Nd = 0.51291, 206Pb/204Pb = 19.36, 207Pb/204Pb = 15.61, 208Pb/204Pb = 39.07
(EM-type endmember) and pyroxenite with 87Sr/86Sr = 0.70309, 143Nd/144Nd = 0.51289,
206Pb/204Pb = 20.03, 207Pb/204Pb = 15.62, 208Pb/204Pb = 39.84 (HIMU-type endmember).
Mixing of melts from these endmembers in proportions ranging from 70% peridotite and 30%
pyroxenite to 28% peridotite and 72% pyroxenite can generate the compositions of the most primitive Gran Canaria shield stage lavas. Combining our results with those from the low
silica rocks from the western Canary Islands [Gurenko et al. (2009) Enriched, HIMU-type
peridotite and depleted recycled pyroxenite in the Canary plume: a mixed-up mantle. EPSL
277: 514-524], at least four distinct components are required. We propose that they are (1)
HIMU-type pyroxenitic component (representing recycled ocean crust of intermediate age)
from the plume center, (2) HIMU-type peridotitic component (ancient recycled ocean crust
stirred into the ambient mantle) from the plume margin, (3) depleted, MORB-type pyroxenitic component (young recycled oceanic crust) in the upper mantle entrained by the plume, and (4)
EM-type peridotitic component from the asthenosphere or lithosphere above the plume center.
Description:
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Contributions to Mineralogy and Petrology 159 (2010): 689-702, doi:10.1007/s00410-009-0448-8.
