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| Titel |
Evidence of prolonged felsic magmatism within the Karoo large igneous province |
| VerfasserIn |
Matti Kurhila, Ilona Romu, Irmeli Mänttäri, Tom Andersen, Arto Luttinen |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250111211
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| Publikation (Nr.) |
 EGU/EGU2015-11300.pdf |
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| Zusammenfassung |
| The Karoo large igneous province (LIP) extends from southern Africa to East Antarctica, and
marks the onset of rifting of these two continents. The main stage of volcanic activity
occurred ~182180 Ma ago, and was mostly mafic in composition. We report new thermal
ionization (TIMS) and secondary ion (SIMS) mass spectrometric U-Pb ages on zircon from
felsic lavas in Lebombo monocline, southern Mozambique and from granitoid intrusions in
Vestfjella, Dronning Maud Land, Antarctica.
Utpostane granite in southern Vestfjella yields a TIMS age of 180.7±1.5 Ma,
complying with the main stage of magmatism in the Karoo LIP. Three rhyolitic beds
intercalating mafic volcanic layers of the Lebombo monocline give SIMS ages of
182±3 Ma, 178±3 Ma, and 172±2 Ma, respectively. The zircon in the oldest of
these can be divided in two groups: (a) internally homogeneous, low U and Pb
zircon and (b) oscillatorily zoned, relatively high U and Pb zircon. The ages of
these groups are ~179 Ma and ~184 Ma, respectively, but they overlap within
error limits, and thus a combined age for this sample is preferred. Finally, an alkali
feldspar granite xenolith from a lamproite dike in Vestfjella has a SIMS age of 165±1
Ma.
Lu-Hf isotopes were analyzed from zircons in the 172 Ma rhyolite sample. They show
fairly homogeneous Hf isotope composition, with initial ÉHf values between +4 and +10.
The corresponding crustal residence ages for the zircons vary between ~300 and ~500 Ma,
implying source recycling. In light of the new data it is thus evident that, while most of the
Karoo LIP may have emplaced within a short time frame, igneous activity continued for at
least ~15 Ma. |
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