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| Titel |
Nd, Sr and Pb isotopic systematics of the Oldoinyo Lengai volcano |
| VerfasserIn |
Anna Balashova, Hannes B. Mattsson, Jörg Keller |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145100
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| Publikation (Nr.) |
 EGU/EGU2017-8999.pdf |
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| Zusammenfassung |
| The Oldoinyo Lengai volcano is characterized by a large range of radiogenic isotope
compositions. The magmatic system of the Oldoinyo Lengai volcano have experienced two
main stages of activity. During the first stage, the magmas originated from an EMI-like
source (87Sr/86Sr = 0.70495-0.75154, 143Nd/144Nd = 0.51248-0.51254,206Pb/204Pb =
18.715-19.078, 207Pb/204Pb = 15.539-15.575, and 208Pb/204Pb = 39.123-39.361). This is in
contrast with products of the second (recent) stage, which are characterized by more
radiogenically depleted isotopic compositions (87Sr/86Sr = 0.70418-0.70467, 143Nd/144Nd =
0.51254-0.51270,206Pb/204Pb = 18.771-19.872, 207Pb/204Pb = 15.561-15.693, and
208Pb/204Pb = 38.760-39.751). The compositional shift can be explained by interaction
(partial remelting and assimilation) between ijolite-series type cumulates belonging to the
first stage of activity at Oldoinyo Lengai, and melilititic to nephelinitic magmas with isotope
characteristics similar to magmas erupted within the neighbouring Lake Natron –
Engaruka monogenetic volcanic field. Isotope mixing calculations and fractional
crystallization modelling indicate that the recent products of Oldoinyo Lengai are
likely the result of partial assimilation in a proportion of 70 to 30. The evolved
rocks, erupted during the transition between the first and the second stage, have
intermediate isotopic compositions, which can be explained by isotope mixing of
Oldoinyo Lengai cumulates and LNE-MVF type magmas in proportion of 90:10
(87Sr/86Sr = 0.70425-0.70487, 143Nd/144Nd = 0.51250-0.51256,206Pb/204Pb =
18.052-18.738, 207Pb/204Pb = 15.440-15.540, and 208Pb/204Pb = 38.238-39.206). |
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