Death and Transfiguration of a Triple Junction in the South Atlantic
M. Ligi,
E. Bonatti,
*
G. Bortoluzzi,
G. Carrara,
P. Fabretti,
D. Penitenti,
D. Gilod,
A. A. Peyve,
S. Skolotnev,
N. Turko
Three major lithospheric plates--Antarctic, South American, and
African--meet in the South Atlantic near Bouvet Island where the
Mid-Atlantic Ridge (MAR), the Southwest Indian Ridge (SWIR), and the
American Antarctic Ridge converge toward a fast evolving triple
junction. A major magmatic pulse has recently built a new, swollen
segment of the SWIR (Spiess Ridge) that is propagating toward the MAR
at a rate of 4 to 5 centimeters per year, disrupting a former
ridge-ridge-ridge (RRR) triple junction. A new triple junction will be
established about 70 kilometers to the north when the propagating
SWIR/Spiess segment will impact with the MAR, probably within the next
1 million years. The American Antarctic Ridge will take advantage of
the MAR/SWIR duel by capturing an approximately 70-kilometer stretch of
MAR, whereas the Antarctic plate will increase its size.
M. Ligi, G. Bortoluzzi, G. Carrara, P. Fabretti, D. Penitenti,
Istituto Geologia Marina, CNR, via P. Gobetti 101, Bologna, Italy.
E. Bonatti, Istituto Geologia Marina, CNR, via P. Gobetti 101, Bologna,
Italy, and Lamont Doherty Earth Observatory of Columbia University,
Palisades, NY 10964-8000, USA.
D. Gilod, Moscow State University, Moscow, Russia.
A. A. Peyve, S. Skolotnev, N. Turko, Geology Institute, Russian Academy
of Sciences, Moscow, Russia.
*
To whom correspondence should be addressed. E-mail:
marcol{at}boigm2.igm.bo.cnr.it
