Structural Architecture of Northern Victoria Land (antarctica) in the Perspective of the Paleo-Pacific Margin of Gondwana

Northern Victoria Land (Antarctica) was part of the active proto-Pacific plate margin of Gondwana, which has been site of protracted convergence during the Paleozoic. This study supplies new insights into the structural architecture of the Transantarctic Mountains in northern Victoria Land, with original structural data on the boundary area between the Bowers and Robertson Bay terranes. This area is characterized by the occurrence of the Millen Schist (MS) belt, that is a high strain equivalent of the adjoining terranes. At present the boundary between the terranes and the MS is marked by two faults with regional relevance: the Leap Year and the Handler faults. Our study reveals that such faults represent an oblique slip system, characterized by positive flower structures, and overprint a transitional pre-existing ductile deformational boundary. Both Leap Year and Handler faults are associated to a significant syn-tectonic fluids circulation, mineralization, and a significant rock-fluid interaction that resemble the one responsible for the gold mineralization, described in the Bowers Mts (northern Victoria Land). The MS belt is made up of two tectonic elements, superposed in a duplex thrust system, with a top-to-NE sense of tectonic transport. This thrust overprints the ductile structures of the MS, that are usually interpreted as due to the Ross-Delamerian Orogeny. Moreover, the CAT is overprinted by LYF and HFS and this testifies to an ongoing transpressional regime. Hence, the overall structural architecture of the Bowers-Robertson boundary is the result of a long-lasting SW-NE oblique contractional regime that started during the Ross-Delamerian Orogeny and was still active after that. The increasing abundance of data indicating a post-Ross contractional event suggests a prolongation into Antarctica of the Lachlan Orogeny of southeastern Australia. The similarity in the structural architecture, in the setting of the gold mineralization and the convergence in rock type and age support a correlation of both the Bowers and the Robertson Bay terranes with the Stawell Zone of the Lachlan Fold Belt. In our new tectonic scenario the Lanterman Fault (northern Victoria Land) plays the same role as the Moyston Fault (southeastern Australia) and the Leap Year and Handler faults are the correlatives of "intra-zone faults" of the Stawell Zone.