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

• Published in: Antarctic Science
• Main Authors: Delor, C.P., Rock, N.M.S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1991
• Subjects: Antarc*; Antarctic Science; Antarctica; East Antarctica; Princess Elizabeth Land
• Online Access: http://dx.doi.org/10.1017/s0954102091000512; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102091000512

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 H 2 O–CO 2 -rich nephelinites, and alkaline lamprophyres (AL), representing H 2 O–CO 2 -rich basanites. Olivine (Fo 46–93 , averaging Fo 75 ) 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% TiO 2 ); titanian phlogopite (up to 10% TiO 2 ); 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% Cr 2 O 3 ) and En 58–76 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.