Antarctic Science
- Antarctic Science / Volume 3 / Issue 04 / December 1991, pp 419-432
- Copyright © Antarctic Science Ltd 1991
- DOI: http://dx.doi.org/10.1017/S0954102091000512 (About DOI), Published online: 14 May 2004
Alkaline-ultramafic lamprophyre dykes from the Vestfold Hills, Princess Elizabeth Land (East Antarctica): primitive magmas of deep mantle origin
AbstractAlkaline dykes tentatively dated at [similar]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. (Received October 1 1990)(Accepted August 1 1991) Key Words: alkaline dyke; geochemistry; lamprophyre; mineralogy; petrology. Correspondence: p1 Dept. Cartes et Syntheses, BRGM, Ave. de Concyr, BP6009 Orléans, France |
