The early Paleozoic Antarctic margin of Gondwana: a synthetic model after twenty years of investigations

The convergence process between the Paleo-Pacific oceanic plate and the Gondwana continental margin during the early Paleozoic led to the construction of the Ross Orogen of the Transantarctic Mountains. For their termination in Victoria Land, variably exotic terranes are the leitmotiv for current geodynamic models. However, recent studies support a different view of the lithospheric sectors compounding this part of the orogen: i. a previously undocumented, Cambrian oceanic magmatic arc (the Tiger arc), along the present northernmost Ross Sea coast, ii. a Robertson Bay crustal sector including continental material, to the west of the Tiger arc, iii. the Bowers arc-backarc complex, developed at the border of iv. the Wilson continental arc, representing the main part of the active Gondwana margin. The updated model presented here includes a first retreat of the subduction zone that gave way to the stretching of the forearc of the Wilson magmatic arc, the trenchward arc migration, the opening of a marginal basin (Bowers backarc) behind the new arc (Bowers arc) and the inception of an additional local subduction zone. Then, resuming of contractional processes led to the closure of the backarc and the underthrusting at high pressure conditions of some of its portions. In the late stage, fast exhumation was coupled in the north with erosion and sediment shed to the north-east, and with extension and potassic magmatism in the south.