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Zircons gneisses and migmatites collected from the Antarctic Peninsula have different core–rim hafnium isotope ratio relationships depending on whether evidence for zircon dissolution is present or absent. Two samples contain inherited zircon that is partially dissolved. In these samples, the 176Hf/177Hf rations of the inherited zircon and new magmatic zircon rims are, on average, indistinguishable and consistent with in situ melting. In such cases the hafnium isotopic composition of the melt was probably strongly influenced by the dissolved zircon component at the source. Variation in 176Hf/177Hf within the magmatic zircon rims from grain to grain suggests that Hf isotopes were only partially homogenized during melt migration; alternatively, zircon growth may have taken place within small volumes of partial melt. Other samples do not preserve textural evidence for zircon dissolution during melt generation; in these samples the 176Hf/177Hf values of the inherited zircon and new magmatic zircon rims are different. The zircon rims apparently suggest a source of less evolved hafnium than that contained within the inherited zircon. Whether this relates to a separate juvenile source or, alternatively, is derived from minerals other than zircon at the source, cannot be resolved. Inherited zircon, irrespective of age, has been strongly influenced by the reworking of a juvenile Late Mesoproterozoic source, suggesting that such crust underlies the Antarctic Peninsula. Our results therefore suggest that Hf isotope analyses provide great potential for future studies investigating the source and processes involved in the generation of crustal melts. [ABSTRACT FROM AUTHOR]

U-Pb detrital zircon geochronology from the upper Cambrian to Devonian part of the Ellsworth Mountains succession, Antarctica, yields dominant late Mesoproterozoic and late Neoproterozoic-Cambrian age populations that are consistent with a provenance from within Gondwana. Hf isotope compositions reveal a source predominantly within west Gondwana and identify a change in provenance up-stratigraphy that coincides with the change of sedimentation setting from active rift to passive margin, which has been independently determined by stratigraphic, structural, and geochemical arguments. For the Late Cambrian Frasier Ridge Formation, late Mesoproterozoic grains have positive Hf values, suggesting derivation from juvenile crust, and late Neoproterozoic-Cambrian grains have Hf values greater than -5, consistent with remelting of similar juvenile late Mesoproterozoic crust during the Pan African-Ross orogenies. Provenance during rifting was from proximal sources from within west Gondwana, most likely, southernmost Africa and basement to the Ellsworth-Whit-more Mountains block. At higher stratigraphic levels where deposition occurred along a passive margin, in the early Ordovician Mount Twiss Member and middle Devonian Mount Wyatt Earp Formation, late Neo-proterozoic-Cambrian grains have Hf values less than -5; this means that early Meso-proterozoic-Archean crust was remelted to generate these zircons. Provenance was from a more expansive source region within west Gondwana, and probably included the Kaapvaal and Congo cratons of south and west Africa. Isolated outcrops of sedimentary rock of uncertain age at Mount Woollard and the Whitmore Mountains have detrital zircon signatures similar to the Frasier Ridge Formation, suggesting correlation with these Late Cambrian deposits. Sedimentary rock from the Stewart Hills contains some late Mesoproterozoic grains with lower Hf values than the previously mentioned samples. This suggests that the Stewart Hills sample has a provenance from within east Gondwana and was possibly deposited on the East Antarctic craton prior to the Ross orogeny and is not part of the displaced Ellsworth-Whitmore Mountains crustal block. [ABSTRACT FROM AUTHOR]