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Alkaline-ultramafic lamprophyre dykes from the Vestfold Hills, Princess Elizabeth Land (East Antarctica): primitive magmas of deep mantle origin

Published online by Cambridge University Press:  14 May 2004

C.P. Delor
Affiliation:
Department of Geology, University of Western Australia, Nedlands WA 6009, Australia Dept. Cartes et Syntheses, BRGM, Ave. de Concyr, BP6009 Orléans, France
N.M.S. Rock
Affiliation:
Department of Geology, University of Western Australia, Nedlands WA 6009, Australia

Abstract

Alkaline dykes tentatively dated at ∼1.3 Ga cut the Vestfold Hills in a consistent N–S to N15°E direction. They form a spectrum between more abundant ultramafic lamprophyres (UML) corresponding broadly to H2O–CO2-rich nephelinites, and alkaline lamprophyres (AL), representing H2O–CO2-rich basanites. Olivine (Fo46–93, averaging Fo75) is abundant only in the UML, but both types carry primary diopsidic clinopyroxene with complex zoning; amphibole (pargasite, hastingsite, kaersutite with up to 8.6% TiO2); titanian phlogopite (up to 10% TiO2); feldspars (orthoclase, anorthoclase, albite and andesine), nepheline (K-poor and Si-rich), ilmenite (up to 1% MgO and MnO), chrome titanomagnetite, and carbonate (magnesian calcite, ferroan dolomite, breunnerite). Lamprophyric peculiarities include the local coexistence of three feldspars, extremely Ti-rich amphiboles and micas, and the presence of globular structures and possibly primary carbonates. Some dykes carry small but abundant lherzolite xenoliths, others carry chromian diopside (1% Cr2O3) and En58–76 orthopyroxene xenocrysts. The dykes represent primitive, mantle-derived magmas which have undergone varying but generally low degrees of polybaric fractionation, together perhaps with mixing of more primitive and fractionated batches, during their ascent through the crust.

Type
Papers—Earth Sciences and Glaciology
Copyright
© Antarctic Science Ltd 1991

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