Precambrian metaigneous xenoliths of Vestfjella: Implications for lithospheric architecture in western Dronning Maud Land, Antarctica

Lamproiteand basalt-hosted xenoliths from Kjakebeinet (73o47’ S, 14o53’ W) and Muren (73o43’ S, 15o02’ W), south Vestfjella, represent unique samples of the unexposed continental crust at the rifted margin of western Dronning Maud Land. The lamproite-hosted xenolith suite indicates 1) heterogeneity of the crust, 2) mainly igneous protoliths, and 3) granulite facies metamorphic conditions. Two leucocratic tonalite gneiss samples yielded U-Pb SHRIMP zircon ages of ~1.3–1.0 Ga (J. Jacobs, personal communication, 2006). The mafic granulites exhibit compositional affinities to Proterozoic lower crustal xenoliths from Lesotho, South Africa [1], and to mantle-derived lower crustal material in general [2]. Interpretation of mineral–whole-rock Sm-Nd isotope data on the mafic granulites is complicated by lamproite overprint; the data are accordant with equilibration of the Sm-Nd -system during Grenvillian and Jurassic magmatic events. In contrast, whole-rock Sm-Nd isotopic data on basalt-hosted leucocratic metatonalite xenoliths show highly negative Nd values (ca. –50 @ 180 Ma) indicative of Archean origin [3]. Overall, the present results imply proximity of the Archean-Proterozoic lithospheric boundary in south Vestfjella. New U-Pb SIMS zircon data on the basalt-hosted and lamproite-hosted felsic metaigneous xenoliths will be available in May 2008 and are expected to facilitate precise dating of tectonic and magmatic events related to the evolution of the poorly exposed crust of East Antarctica.