Geochronology and geochemistry of Ferrar rocks from North Victoria Land, Antarctica.
Brotzu, Pietro; Capaldi, Giuseppe; Civetta, Lucia; Orsi, Giovanni; Gallo, Gabriella; Melluso, Leone
European Journal of Mineralogy Volume 4 Number 3 (1992), p. 605 - 618
published: Jun 11, 1992
manuscript accepted: Nov 7, 1991
manuscript received: Apr 5, 1991
ArtNo. ESP147050403019, Price: 29.00 €
Abstract K-Ar determinations on two igneous units from North Victoria Land, Antarctica, representative of the Ferrar Dolerite and Kirkpatrick Basalt, yield dates ranging from 144 to 180 Ma. The oldest date is in agreement with a Rb- Sr isochron age of 182 Ma provided by most of the analysed samples. It is considered to represent the age of the magmatic activity which produced the two suites ; younger dates are attributed to argon loss subsequent to cooling. The chemical compositions of the rocks range from basaltic andesite to dacite. Major-element mass-balance, trace-element modelling, isotopic and geothermometric data, all imply a closed-system differentiation history from basaltic andesite to dacite. The basaltic andesites are characterized by high initial 87Sr/86Sr ratios (clustering around 0.7114) and low initial 143Nd/144Nd ratios (0.5121), high concentrations of incompatible elements, and relatively low abundances of Na2O, Nb, Ti and P. The normalized trace element contents of the least evolved basaltic andesite studied are intermediate between those of low-TiO2 and high-TiO2 lavas from the Mesa Range to the south. Major and trace element modelling shows that the studied basaltic andesites can be derived by crystal fractionation processes from the least differentiated Iow-TiO2 rocks and, in turn, may generate high-TiO2 rocks by crystal fractionation