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Rosaria Palmeri, Università di Siena (Italy)
Sonia Sandroni, Università di Siena (Italy)
Gaston Godard, Université Paris VII (France)
Carlo Alberto Ricci, Università di Siena (Italy)
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In northern Victoria Land (Antarctica), at the Pacific termination of the Transantarctic Mountains, a major suture zone separates the inboard Wilson Terrane, characterized by low- to high-grade metamorphism, from two low-grade outboard terranes, the Bowers and the Robertson Bay Terranes (e.g. Ricci & Tessensohn, 2003). This Wilson?Bowers boundary, a complex fault zone, runs more than 400 km from the Ross Sea coast to the Pacific Ocean and is characterized by the presence of discontinuous bodies of mafic-to-ultramafic rocks with a metamorphic grade ranging from medium-P amphibolite facies to ultrahigh-P eclogite facies (Kleinschmidt et al., 1987; Ricci & Tessensohn, 2003; Palmeri et al., 2007). The boundary is best exposed in two areas, namely the Lanterman Range and the Mountaineer Range (Capponi et al., 1999).
In the Lanterman Range, the high-to-ultrahigh-P rocks are part of the Gateway Hills Metamorphic Complex, which discontinuously outcrops between the external Bowers Terrane and the internal complexes of the Wilson Terrane (Talarico et al., 1998). The latter is characterized by a low-to-medium-P regime metamorphism and by abundant intrusions of the Granite Harbour Intrusive (Ricci et al., 1997). The Dessent Metamorphic Complex is a narrow tectonic slice of the Mountaineer Range, which as the Lanterman Range, occurs between the metavolcanic rocks of the Bowers Terrane at the eastern side and the Wilson Terrane at the western side. The Dessent metamorphic Complex shows abundant mafic rocks (as the Gateway Hills metamorphic Complex) but only a medium-P metamorphism (as the rocks of the Bernstein Metamorphic Complex of the Lanterman Range).
The Bernstein Metamorphic Complex and the Gateway Hills Metamorphic Complex of Lanterman Range, together with the Dessent Metamorphic Complex of the Mountaineer Range, are regarded as a subduction zone mélange (Ricci et al., 1997) and so represent key units for the understanding of the subduction?collision system during the palaeo-Pacific lithosphere subduction under the Gondwana margin.
New petrographic investigations on amphibolites from the Dessent Metamorphic Complex evidenced some peculiar assemblages as the tschermakite+gedrite+garnet+staurolite paragenesis so far unknown along the suture zone. The assemblage talc+anthophyllite+Mg-hornblende+chlorite could also testify the presence of metamorphosed ultramafic rocks. New petrological and geochemical investigations on these mafic-to-ultramafic rocks from the Dessent Metamorphic Complex are presented here. The results are compared with the rocks from the Lanterman Range to increase the knowledge on the "high-T mélange" that occurs in the suture zone along the palaeo-pacific margin of Gondwana.
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