Jurassic dikes of Vestfjella, western Dronning Maud Land, Antarctica: Geochemical tracing of ferropicrite sources

Ferropicrites and their differentiates make up a geochemically distinctive group of dikes that crosscut Jurassic continental flood basalts of the Karoo large igneous province at Vestfjella, western Dronning Maud Land. Antarctica. The Vestfjella ferropicrites can be divided into two geochemical types: The depleted ferropicrites have (La/Sm)(N) of 1.2-1.3, (Sm/Yb)(N) of 4.5, initial epsilon(Nd) from +7 to +8, initial epsilon(Sr) from -18 to -19, and show relative depletion of highly incompatible elements, but pronounced enrichment of V; The enriched ferropicrites have (La/Sm)(N) of 1.7, (Sm/Yb)(N) of 5.1-5.4, initial epsilon(Nd) from +3 to +4, initial epsilon(Sr) from 0 to + 1, and show general enrichment of incompatible trace elements. The immobile incompatible element signatures of the ferropicrites have not been significantly affected by alteration, fractional crystallization, or contamination. Based on primitive olivine phenocrysts (Fo(79-88)) and high epsilon(Nd) values, the depleted ferropicrites represent near-primary melts derived from anomalous hot mantle sources. Overall, geochemical compositions favor a pyroxenite source for the ferropicrites. Unusually high (V/Lu)(N) values of the depleted ferropicrites indicate an affinity to oceanic Fe-Ti gabbros and geochemical modeling favors such a recycled mantle source component in them. The enriched ferropicrites probably represent near-primary melts, but this cannot be confirmed. They may also record an exceptionally Fe-rich source component, but their high Fe contents stem at least partly from relatively low-degree melting at high pressures, as indicated by the high (La/Sm)(N) and (Sm/Yb)(N) rados. Examination of a global ferropicrite dataset reveals that the recycled Fe-Ti gabbro component is detectable in many ferropicrites. (C) 2008 Elsevier B.V. All rights reserved.