Seismic Imaging of the Magallanes-Fagnano Fault System (Tierra del Fuego Region)

YAGUPSKY, D.L.; TASSONE, A.; LODOLO, E.; MENICHETTI, M.; VILAS, J. F.

Buenos Aires

Simposio; Geosur 2004; 2004

The Magallanes Fagnano Fault System (MFS) is one of the principal tectonic lineament of the modern sinistral transform boundary between the South America and Scotia plates (Fuenzalida, 1972; Dalziel, 1989). This 3000 km-long boundary runs from the Antarctica-South America-Scotia triple junction in the vicinity of the Taitao Peninsula to the Tierra del Fuego Atlantic offshore, crossing the southernmost tip of South America along the Magallanes Strait, the Seno Almirantazgo (Winslow, 1982) and the northern margin of lago Fagnano (Klepeis, 1994; Lodolo et al., 2002 a and b). It continues under the lineal depression of the Turbio and Irigoyen rivers (Lodolo et al., 2002b), reaching the Atlantic shoreline in coincidence with the estuary of the Irigoyen river (Ghiglione, et al. 2002; Lodolo et al., 2003). In the continental platform the MFS strikes E-NE (Lodolo et al., 2002a and b; this work) and parallels the northern slope of both the North Scotia Ridge and the Burdwood Bank. It was proposed (Klepeis, 1994) that the present MFS might have undergone strike-slip movements before the Oligocene development of the transform boundary between the Scotia and South American plates along the North Scotia Ridge. Since Middle Cretaceous, the inner parts of Fueguinian Andes would have undergone transcurrent tectonics in the Beagle Channel region (Cunningham, 1993 and 1995), and other strike-slip lineaments, paralleling the MFS, are found in the Tierra del Fuego region. Herein we present new geophysical data which allow us to characterize the behavior of different segments of the MFS in the offshore areas within the Argentine platform. This new information is analyzed in combination with the available geological and geophysical data from the eastern (Burdwood Bank) and western regions (onland Tierra del Fuego). Four seismic profiles which traverse the strike of the MFS are shown in Fig. 1. Two principal pull-apart basins (Western and Eastern Basins, Fig. 1), associated with the MFS, were recognized: Both basins are strongly asymmetric and are bounded by a sub-vertical discontinuity which reaches the ocean floor. The sedimentary architecture of the two basins is similar, indicating a common tectonic evolution. Similar asymmetric basins are typically found along transform plate boundaries and displaying increasing sedimentary thickness towards the fault and normal-strike extension (Ben-Avraham, 1992).