CONTINENTAL FRAGMENTATION ALONG THE SOUTH SCOTIA RIDGE TRANSCURRENT PLATE BOUNDARY (NE ANTARCTIC PENINSULA)

The study of the South Scotia Ridge on the basis of swath bathymetry, multichannel seismic and magnetometry profiles, obtained during the HE SANT 92/93 cruise and complemented with satellite gravimetry and seism icity data illustrates the tectonics of the region. The thinned contin ental crust fragments of the ridge are bounded by oceanic crust of the Scotia Sea to the North and Powell Basin to the South. The northern b oundary represents the contact between the Scotia and Antarctic plates . This boundary is a sinistral transpressional fault with transtension al segments and moderate recent tectonic activity. Another fault locat ed at the: southern boundary appears inactive and does not reveal any features that would enable the kinematics to be determined. Both fault s have associated steep scarps since they separate oceanic and contine ntal crust types. The most significant active deformation lies in the axial depression of the ridge, within a band delineated by fault syste ms with WSW-ENE and SW-NE strikes. These faults develop pull-apart bas ins, which separate the northern and southern blocks of the: ridge. Th e northern block is being fragmented from the Antarctic Plate by a zon e of transtensive faults, and is probably a crustal element independen t of the Antarctic Plate. The axial depression, which crosses the ridg e slightly obliquely, is characterized by deep basins locally more tha n 5000 m deep and associated high seismicity. The fault geometry and e arthquake focal mechanisms indicate an active sinistral transtensive r egime for the fault system, although it may locally have transpressive regimes depending on the fault plane and the stress field orientation s. The internal basins are characterized by an asymmetric development showing itself as depositional wedges generally thickening northward. Deposits onlap the southern margins and are affected by normal faults in the northern margins. The seismicity around the Scotia Plate shows that the present stresses are compressive along the northern boundary with the South American Plate (sigma(1) SW-NE and subhorizontal) and a long the western boundary with the Antarctic Plate (sigma(1) WNW-ESE a nd subhorizontal). For the South Scotia Ridge, however, sigma(1) is st eeply inclined and sigma(3) is subhorizontal with a NW-SE trend. The s tress distribution in Bransfield Strait is similar to the ridge and th e recent extension could be partially explained by the westward contin uation of the active fault system of the central South Scotia Ridge. T he fragmentation of continental crustal blocks, due to the tectonic ac tivity along the transcurrent plate boundaries, is a mechanism that co ntributes to the deformation of the northeastern end of the Antarctic Peninsula. This area appears appropriate for the analysis of continent al plate fragmentation processes.