Ultrahigh-pressure metamorphism at the Lanterman Range (northern Victoria Land, Antarctica)



Northern Victoria Land is a key area for the Ross Orogen—a Palaeozoic fold belt formed at the palaeo-Pacific margin of Gondwana and also known as the Delamerian and Tyennan Orogeny in southern Australia, and Tasmania, respectively. A narrow and discontinuous high- to ultrahigh-pressure (HP/UHP) belt, consisting of mafic and ultramafic rocks (including garnet-bearing types) within a metasedimentary sequence of gneisses and quartzites, is exposed at the Lanterman Range (northern Victoria Land), at the boundary between two main lithotectonic terranes (the Wilson and Bowers terranes). Mesostructural and microstructural relations between eclogitic boudins and country gneisses are, in some areas, characterized by interlayering with sharp contacts on a cm scale. Geological, petrological and geochronological studies indicate that mafic, ultramafic and felsic host rocks underwent a common metamorphic evolution with an UHP eclogite–facies stage ≈ 500 Ma ago at temperatures of up to ≈ 850°C and pressures up to 3.3 GPa. The retrograde P–T path is similar and, indeed, it overlaps in every lithology; it is a nearly isothermal path from UHP conditions up to deep crustal levels, and becomes a cooling–unloading path from intermediate to shallow levels. The discovery of UHP rocks at the Lanterman Range yields eclogite–facies rocks of this area among the rare UHP rocks of the world and represents the only known locality in Antarctica and along the entire palaeo-Pacific margin of Gondwana during the Ross–Delamerian–Tyennan Orogen. Copyright © 2010 John Wiley & Sons, Ltd.