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1 British Antarctic Survey, Natural Environment Research Council, Madingley
Road, High Cross, Cambridge CB3 0ET, UK
2 NERC Isotope Geosciences Laboratory, Keyworth, Nottingham NG12 5GG, UK
* E-mail: t.riley{at}bas.ac.uk
Jurassic dykes of western Dronning Maud Land (Antarctica) form a minor
component of the Karoo large igneous province. An extensive local dyke swarm
intrudes Neoproterozoic gneisses and Jurassic syenite plutons on the margins
of the Jutulstraumen palaeo rift in the Svedrupfjella region. The dykes were
intruded in three distinct episodes (
204, 176 and 170 Ma). The
204 Ma dykes are overwhelmingly low-Ti, olivine tholeiites including some
primitive (picritic) compositions (MgO >12 wt.%;
Fe2O3 >12 wt.%; Cr >1000 ppm; Ni >600 ppm).
This 204 Ma event precedes the main Karoo volcanic event by 25 Ma, so any
correlations to the wider province are difficult to make. However, it may
record the earliest phase of rift activity along the Jutulstraumen. The 176 Ma
dyke event is more intimately associated with the two syenite plutons. The
dykes are alkaline (basanite/tephrite) and were small-degree melts from an
enriched, locally derived source and underwent at least some degree of
interaction with a syenitic contaminant. This 176 Ma dyke event is
widespread elsewhere in the Karoo (southern Africa and Dronning Maud Land).
Later-stage (170 Ma) felsic (phonolite-comendite) dykes intrude the 176 Ma
basanite-tephrite suite and represent the last phase of magmatic activity in
the region.
KEYWORDS: Gondwana, basanite, tephrite, phonolite, syenite, rift
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