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Creator |
4989dd10527e94ef140e45e8c9fb07e6 |
| 22342 |
Creator |
f1077bcde0d9eb87b9fa30b4c97d8eb9 |
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Creator |
a0a25b9a30e54e79f6b57b268aa4ebb0 |
| 22342 |
Creator |
ext-c3316052bfcdce6312f3db54ece1517c |
| 22342 |
Date |
2010 |
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Is Part Of |
p0012821X |
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Is Part Of |
repository |
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abstract |
Variations in the Fe/Mn ratio and Osmium isotopes in magnesium-rich mafic rocks from
plume-related volcanic provinces have been exploited to imply the entrainment of core
material in mantle plumes and the involvement of ancient recycled oceanic lithosphere.
Here we present new major and trace element, <sup>187</sup>Os/<sup>188</sup>Os ratios
and precise Fe/Mn ratios on a suite of MgO-rich basalts, picritic basalts and ankaramites
from the 30 Ma Ethiopian flood basalt province that shed new light on these arguments.
The lavas show a range of compositions with MgO varying from 5 to 20 wt.% although
the primary magma is inferred to have an MgO content of 15–16 wt.%. The lavas are
also characterised by low Al<sub>2</sub>O<sub>3</sub> contents (7–9 wt.% at 15 wt.%
MgO), implying an origin from 150 km depth at a temperature in excess of 1600 °C,
consistent with an origin in the early phases of Afar mantle plume activity. Osmium
isotopes in samples with > 10 wt.% MgO are unradiogenic with <sup>187</sup>Os/<sup>188</sup>Os
< 0.127 while those with lower MgO define a positive correlation with Re/Os and appear
to have been contaminated by crustal material. Fe/Mn ratios determined by ICP-MS vary
from 65.4 to 78.5 in rocks with > 10 wt.% MgO and show greater variation to both higher
and lower values in less magnesian samples. These values are high compared with MORB
and Icelandic basalts, comparable with the Fe/Mn ratios of Hawaiian and other selected
ocean island basalts, and are a characteristic of the primary magma. There is no evidence
to suggest that Fe/Mn is fractionated during peridotite melting at low pressures less
than 5 GPa, implying in agreement with previous studies that high Fe/Mn ratios are
a compositional feature of the magma source region. The lack of association of radiogenic
<sup>187</sup>Os/<sup>188</sup>Os with the high Fe/Mn ratios of the Ethiopian picritic
basalts calls into question the link to possible entrainment of core material in the
source of the Afar mantle plume. Similarly, the unradiogenic <sup>187</sup>Os/<sup>188</sup>Os
ratios preclude a significant contribution from ancient recycled oceanic lithosphere.
An alternative model is suggested in which melts generated at high pressures (> 7
GPa) during the initial turbulent ascent of the Afar plume head form pyroxene rich
veins with high Fe/Mn ratios and high incompatible element contents in a peridotite
matrix. These highly fertile source regions contribute significantly to melt compositions
during the early phases of plume emplacement. |
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authorList |
authors |
| 22342 |
issue |
3-4 |
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status |
peerReviewed |
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volume |
296 |
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type |
AcademicArticle |
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type |
Article |
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label |
Rogers, Nick W. ; Davies, Marc K. ; Parkinson, Ian J. and Yirgu, Gezahegn (2010).
Osmium isotopes and Fe/Mn ratios in Ti-rich picritic basalts from the Ethiopian flood
basalt province: no evidence for core contribution to the Afar plume. Earth and Planetary
Science Letters, 296(3-4) pp. 413–422. |
| 22342 |
label |
Rogers, Nick W. ; Davies, Marc K. ; Parkinson, Ian J. and Yirgu, Gezahegn (2010).
Osmium isotopes and Fe/Mn ratios in Ti-rich picritic basalts from the Ethiopian flood
basalt province: no evidence for core contribution to the Afar plume. Earth and Planetary
Science Letters, 296(3-4) pp. 413–422. |
| 22342 |
Title |
Osmium isotopes and Fe/Mn ratios in Ti-rich picritic basalts from the Ethiopian flood
basalt province: no evidence for core contribution to the Afar plume |
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in dataset |
oro |