Enriched mantle - Dupal signature in the genesis of the Jurassic Ferrar tholeiites from Prince Albert Mountains (Victoria Land, Antarctica)

The major, trace (including rare earth) element abundances, and Sr-Nd-Pb isotopic compositions, have been analysed for andesitic basalt and andesitic sills and lavas of the Jurassic Ferrar Magmatic Province, Prince Albert Mountains, Antarctica. The typical "crustal signature" of the Ferrar magmatism, characterized by relatively high SiO2, LREE and LILE contents in these samples, is associated with high Sr-87/Sr-86 and low Nd-143/Nd-144. Systematic correlations of major and trace elements indicate that fractional crystallization mas important. However, increases in incompatible elements are positively correlated with initial Sr-87/Sr-86, suggestive of crustal assimilation processes. The observed correlations between initial Sr-87/Sr-86 and LREE enrichments have been modelled by an AFC process, starting from the least evolved sample and assuming the compositions of the orthogranulites of Victoria Land as contaminants. The REE patterns of the least evolved Ferrar rocks approach those of E-type MORE, differing only by higher LREE/IREE. The enrichment in LREE, accompanying high initial Sr-87/Sr-86, Pb-207/Pb-204 and low Nd-143/Nd-144 compared with E-type MORE, can be explained by interaction of "primary Ferrar basalt" with crystalline basement. We propose a petrological model whereby Ferrar magmas were generated through high degrees of melting of an E-type MORE mantle source, and subsequently these "primary" melts underwent AFC processes inheriting a crustal signature. The Sr-Nd-Pb isotopic compositions required by the AFC model for the primary Ferrar basalt are similar to those of the Dupal signature of the oceanic basalts of the Southern Hemisphere (Hart 1984). Transantarctic Mountains would have been located inside the Dupal anomaly in pre-Gondwana dispersion times.