Magmatic belts in accretionary margins, a key for tectonic evolution: the Tonalite Belt of North Victoria Land (East Antarctica)

Occurring in the Early Palaeozoic palaeomargin of the East Antarctica Craton, the Tonalite Belt of North Victoria Land is a narrow linear magmatic belt up to 200 km long, made up of strongly foliated tonalitic and granodioritic intrusions. They were synkinematically emplaced into the Lanterman-Murchison Shear Zone, a major tectonic structure across which different tectono-metamorphic terranes were accreted during the Late Cambrian Ross Orogeny. The deformational and kinematic features of the intrusions indicate that strain and displacement during terrane accretion were partitioned into oblique thrust, high-angle thrust and strike-slip shear zones. From this it is deduced that a transpressional regime prevailed during Early Palaeozoic deformation and terrane accretion. This and other magmatic belts which exploited major tectonic structures in collisional margins, such as the Coast Plutonic Complex of NW America, are basic keys for understanding deformational processes and kinematic regimes during terrane accretion. Moreover, the occurrence of such types of magmatic belts might be regarded as a reliable indication of large scale strike-slip motion between accreting terranes in an oblique convergent setting