Magmatic History and the High-Grade Geological Evolution of the Vestfold Hills, East Antarctica

Detailed mapping of intrusive relations that are preserved in Archaean orthogneisses in the Vestfold Hills has allowed a reconstruction of the magmatic history of the terrane, which in turn constrains the nature and timing of metamorphism and deformation. Field observations indicate that a number of spatially, temporally and compositionally distinct intrusions were emplaced throughout the Crooked Lake magmatic episode (2501 and 2477 Ma). When combined with new structural observations the distribution of Crooked Lake orthogneiss constrains the scale of tectonic repetition to be localised, with fold wavelengths of ca. 500 m or less. Regional-scale tectonic repetitions of major units as previously reported have not been supported by our mapping, which instead shows that the amount of strain associated with the main folding and fabric producing event (D₂) is heterogeneous. In a region of relatively high strain, a previously defined gneiss unit, the Tryne meta-volcanics, is demonstrated to be a tectonic intercalation of lithologies rather than a volcanic succession. Early structural domains preserved in low strain areas illustrate that the oldest gneisses, such as the Chelnok Paragneiss, retain vestiges of a tectonic history predating the ca. 2500 Ma (D₁-M₁ and D₂-M₂) high-grade events. The comprehensive geological framework determined for the Vestfold Hills is unlike the history so far established for the reworked Archaean crust in the adjacent Rauer Group and these terranes are considered to have been separate entities at the end of the Archaean.