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Middle Jurassic ultramafic lamprophyre dyke within the Ferrar magmatic province, Pensacola Mountains, Antarctica

Published online by Cambridge University Press:  25 June 2018

P. T. Leat ,
T. R. Riley ,
B. C. Storey ,
S. P. Kelley  and
I. L. Millar
P. T. Leat*
Affiliation:
British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
T. R. Riley
Affiliation:
British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
B. C. Storey
Affiliation:
British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
S. P. Kelley
Affiliation:
Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
I. L. Millar
Affiliation:
British Antarctic Survey, c/o NERC Isotope Geoscience Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK
*
*E-mail: [email protected]
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Abstract

An ultramafic lamprophyre dyke is described from the otherwise tholeiitic Ferrar magmatic province of Antarctica. We report an Ar-Ar age of 183 ± 2.2 Ma for the dyke, indistinguishable from those of the Ferrar tholeiites. However, the dyke has mineralogical and major and trace element compositions, and radiogenic isotopes ratios, very different from the Ferrar tholeiites. The sample consists of olivine and rare clinopyroxene phenocrysts with perovskite and spinel microphenocrysts in a groundmass of amphibole, nepheline and biotite. Carbonatitic globules contain calcite, dolomite, Fe-rich carbonate, nepheline, biotite, orthoclase, pyrite, clinopyroxene, apatite and silicate glass, and were formed by liquid immiscibility. The rock is mildly potassic and classifies as an ouachitite. It is strongly enriched in both moderately and highly incompatible trace elements and is the first high-Ti rock to be described from the Ferrar magmatic province. The rock has similar initial 143Nd/144Nd to OIB, notably Bouvet, Crozet and Réunion, but significantly higher initial 87Sr/86Sr. The lamprophyre magma is interpreted as having been generated by low-degree partial fusion of metasomatized lithospheric mantle as a result of heat conducted from an underlying Jurassic mantle plume. The same mantle plume was probably also responsible for generating one of the world’s largest layered gabbro bodies, the Dufek-Forrestal intrusions.

Keywords

ultramaficlamprophyredykeFerrarPensacola MountainsAntarctica
Type
Research Article
Information
Mineralogical Magazine , Volume 64 , Issue 1 , February 2000 , pp. 95 - 111
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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