| Abstract: | Field investigation together with a number of geochemical petrographical analyses, as well as absolute K-Ar age determinations and geophysical data, allow the recognition of an evolutionary sequence of geodynamic events which have affected the northern region of Antarctic Peninsula and the adjacent islands.A significant volcanic calc-alkaline belt, which developed on the northwestern margin of the Antarctic Peninsula during the Cretaceous to Middle Tertiary, is indicative of active subduction of the Antarctic plate in that area. This activity decreases during the Lower Miocene, giving way to an expansive phase represented by the Bransfield Rift. These extensional processes are dominant during the Pliocene, creating a rift system in southeastern Bransfield towards Larsen. Both the Bransfield and Larsen systems comprise one “fan-like rift system”, associated with the Prince Gustav Rift and the Scotia Arc micro-plate. Ejection of abundant pyroclastic material generated a large plateau of palagonite hyaloclastites of basaltic alkaline composition. During the Pleistocene-Recent, the extensional activity continued, as evidenced by the active volcanic fractures represented in Bransfield by the Deception, Penguin and Bridgeman volcanic centres; in the Prince Gustav Rift by Paulet Islands and others, and in Larsen by the Coley, Seal Nunatak and Argo volcanic centres. The latter is characterized by basaltic olivine-alkaline effusions. These rifts and the continental blocks are affected by a series of fractures with a N60°–70°W strike, which could be directly associated with the Hero Fracture Zone extending northwest of the South Shetland Islands Trench. |
