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| Titel |
The role of mantle plumes in the formation of Large Igneous Provinces: A noble gas isotope study from the Etendeka province of Namibia |
| VerfasserIn |
Nicole A. Stroncik, Marc-Sebastian Krienitz, Samuel Niederman, Robert B. Trumbull, Chris Harris |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076924
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| Zusammenfassung |
| The magmatic history of the Earth is characterised by the episodic appearance of enormous
magmatic events, during which large volumes of mainly mafic magmas are generated and
emplaced by processes distinct from seafloor spreading or subduction. The so-called Large
Igneous Provinces (LIPs) produced during these events are mainly created within less than 10
Ma, with the bulk of magmatism occurring in the first Ma. The favoured explanation for LIP
formation is magmatism resulting from plume head decompressional melting. However, the
evidence for this theory is mixed and has been challenged lately. Conventional geochemical
tracers (Sr, Nd or Pb isotopes or trace elements) generally used to characterise the mantle
sources of a magmatic sample are relatively ambiguous in this context, because (1)
various mantle reservoirs can contribute to LIP formation and it is unclear which
of them are located in the deep mantle, (2) magmas can be contaminated during
their ascent through the lithosphere and crust and (3) trace element patterns are
also controlled by the degree and depth of melting. In this respect, the principal
advantages of noble gases as geochemical tracers for magmatic processes are related
to (1) their chemical inertness - they are only modified by nuclear, melting and
degassing processes, (2) the large and indicative isotope variations between the
various terrestrial reservoirs and (3) their relatively low abundance in the solid
Earth.
Here we present He, Ne, and O-isotope data from fresh olivines as well as REE and Sr,
Nd, and Pb isotope whole rock data derived from dolerite dykes and related rocks from the
southern Etendeka province of Namibia. The He-isotope data show a range from
radiogenic values of 0.15 ± 0.01 RAto mantle values of 12.03 ± 0.28 RA. The
radiogenic He isotope ratios are indicative of crustal contamination during magmatic
evolution, which is generally supported by the Ne and O isotope data. The upper
range of the He isotope data is higher than the typical MORB value (8 ± 1 RA),
indicating the involvement of a more primitive mantle source in the formation of
the investigated magmas. Such an involvement is also supported by the observed
co-variations between the He isotopes and the Sr and Pb isotopes as well as the REEs. |
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