The Bouvet triple junction has been proposed to have evolved as a
ridge-fault-fault (RFF) type between 20 and 10 Ma, connecting the
southernmost Mid-Atlantic Ridge (SMAR) with the Bouvet and
Conrad transforms, to the east and west, respectively. We surveyed
immediately north of these two transforms with HAWAII-MR1 sidescan
and Simrad EM12 multibeam sonars, on seafloor that would have
originally been created at the SMAR close to its junction with the two
transforms. The sonar data reveal that SMAR fabrics on the Bouvet
and Conrad sides, when corrected for plate rotation, are parallel to each
other, so they were most likely formed at the same spreading ridge and
confirm that the triple junction was indeed RFF. Our second major
result is that the SMAR fabrics are extensively cross-cut by normal
faults, over most of the 400 km surveyed along both transforms and
most intensely north of the Bouvet transform. Growth faults and
faults affecting the sediment surface in multichannel seismic images
show that the deformation has been long-lived and is probably on-
going. Since the orientations of the cross-cutting faults are similar to
those of shear zone tension fractures, we interpret these areas to be
transtensional zones. This extent of deformation adjacent to major
oceanic transforms is rare and we develop a number of ideas to help
explain its origin.
N. C. Mitchell, R. A. Livermore, P. Fabretti and G. Carrara,
The Bouvet triple junction, 20 to 10 Ma, and extensive transtensional deformation adjacent to the Bouvet and Conrad transforms,
J. Geophys. Res., 105, 8279-8296, 1999.