Copyright by Nysha Chaderton 2009 - The University of Texas at ...

and Westbrook, 1987), are thought to be responsible for the 3,000 m of rise on the
prism’s interior. Brown and Westbrook (1987) identified the presence of WNW-
ESE Atlantic basement ridges beneath the prism using long-range side-scan sonar
images and seabeam bathymetry. Their investigations show a correlation between
the orientation of these basement ridges and the structural features of the prism.
The west- and east-facing thrust faults and associated piggyback basins and
sediment ridges are oriented roughly parallel to the deformation front. However,
at oblique angles to these roughly north-south features are the NW-SE-trending
extensional faults of the Barbados Ridge, which have a similar orientation to that
of these basement ridges. Compression and thrust faulting occur on the west side
of the Barbados Ridge, where basement ridges act as a buttress to westward
movement, causing thrusting and uplift to occur.
Inner Forearc Deformation Front
The Inner Forearc Deformation Front (IFDF) delimits the east margin of
the Tobago Forearc Basin and forms the boundary between the highly deformed
sediments of the accretionary prism and the relatively undeformed sediments of
the Tobago Forearc Basin (Figures 4.4 and 4.6). It is characterized by east dipping
thrust faults that are the result of interaction between the downgoing Atlantic
Plate and the strong crystalline basement.
Tobago Forearc Basin
The Tobago Forearc Basin, filled with as much as 12 km of sediment,
shows little evidence of deformation at its center (Figure 4.6). Several small-scale
normal faults along the west and north margins of the basin, confined to the
youngest part of the section have very minor throw and appear to terminate at a
common shallow horizon. It is not uncommon for normal faults to occur on the
stable flanks of forearc basins, and it has been speculated that they form as a
53