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| Titel |
87Sr/86Sr in spinel peridotites from Borée, Massif Central, France: melt depletion and metasomatism in the sub-continental lithospheric mantle |
| VerfasserIn |
Caroline Barnett, Jason Harvey |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135689
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| Publikation (Nr.) |
 EGU/EGU2016-16586.pdf |
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| Zusammenfassung |
| Radiogenic isotopes and elemental concentrations in peridotite xenoliths may be used to
model the timing and degree of partial melting in the upper mantle, but this primary melt
depletion signature may be overwritten by subsequent episodes of melt or fluid infiltration.
Spinel peridotites from the Maar de Borée, Massif Central, France have mainly poikilitic
protogranular textures and clear petrographic evidence of a melt phase apparently unrelated
to host basalt infiltration. Bulk rock major and compatible trace element concentrations are
consistent with varying degrees of partial melting but incompatible trace element
concentrations indicate cryptic metasomatism in some samples. Lithophile trace
element mass balance cannot always be reconciled by the inclusion of the chemically
characterized melt phase and suggest a contribution from a trace abundance grain boundary
phase1.
87Sr/86Sr values for unleached bulk rocks and clinopyroxene mineral separates are higher
than those for their leached equivalents, consistent with the removal of a radiogenic grain
boundary phase. While unleached bulk rock 87Sr/86Sr is sometimes indistinguishable (within
error) from its constituent unleached clinopyroxene, in two samples they show distinct
patterns, as do the REE trends in these two xenoliths.
BO01-01 bulk-rock is LREE-enriched (La/YbN = 3.6)2, and constituent clinopyroxene
shows a similar relative enrichment trend. Bulk-rock 87Sr/86Sr is 0.70342±1 while
that of clinopyroxene is lower at 0.70332±2. Clinopyroxene modal abundance is
11%.
BO01-03 bulk-rock is only slightly LREE-enriched (La/YbN = 1.2) and both bulk-rock
and clinopyroxene show a generally flatter profile. Bulk-rock 87Sr/86Sr is 0.70285±1 while
that of clinopyroxene is in this case higher at 0.70296±2. Clinopyroxene modal abundance is
also higher at 15%, consistent with a greater contribution by clinopyroxene to the bulk-rock
Sr-isotope budget.
The results appear to be inconsistent with a simple model of single-stage melt extraction
followed by single-stage trace element enrichment and imply a more complex sequence of
possibly multiple melt depletion and metasomatic events, similar to those described by
previous authors, and likely to include infiltration of C-O-S-H-rich fluids and/or silicate
melt.3,4,5,6,7
Bodinier et al. (1996) Geochim Cosmochim Ac, 60, 545 – 550.
Palme & O’Neill (2004) Treatise Geochem 2(01), 1-38.
Zangana et al. (1997) Contrib Mineral Petrol, 127, 187 – 203.
Lenoir et al. (2000) Earth Planet Sci Lett, 181, 359 – 375.
Harvey et al. (2010) Geochim Cosmochim Ac, 74, 293 – 320.
Harvey et al. (2012) J Petrol, 53, 1709 – 1742.
Harvey et al. (2015) Geochim Cosmochim Ac, 166, 210 – 233. |
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