Approximate surface projection on South Atlantic Ocean of the Bouvet triple junction where the white lines of the three mid-oceanic ridges intercept. Other nearby associated named fracture zones are also shown in orange. Click to expand map and obtain interactive feature details.[1]
There are two prominenttransform valleys in the area: Conrad transform and Bouvet transform. Both transforms are named asfracture zones.[4] Conrad transform is named afterUSNS Robert D. Conrad (T-AGOR-3).[4] Bouvet Island is the highest point on the southern wall of the Bouvet transform and was formed 2.0–2.5 million years ago.[5]
There has been complex development over time with the first Bouvet triple junction being formed about 119–124Ma, the second about 93–105 Ma, and the third at 25–30 Ma.[6]Up to 10 million years ago this third junction of the Mid-Atlantic Ridge and the two deep transform valleys of Conrad and Bouvet met in one point. Thus the triple junction was of the ridge-fault-fault (RFF) type.[7] Conrad transform, known as the Conrad fracture zone,[2] stretching to the west, connected the end of the Mid-Atlantic Ridge to the South American-Antarctic Ridge. Bouvet transform, known as the Bouvet fracture zone,[2] linked it to the Southwest Indian Ridge on the eastern side,[7] and this is known to be the oldest part of the current triple junction at 8 Ma.[8]
Currently the Conrad transform and Bouvet transform are no longer connected to each other. The Mid-Atlantic Ridge is retreating northward, at a rate of 11 mm/a (0.43 in/year)[citation needed]. New spreading sections of the South American-Antarctic Ridge and the Southwest Indian Ridge are growing northward from the eastern end of Conrad transform and the western end of Bouvet transform respectively, striving for the shifting triple point. Thus the Mid-Atlantic Ridge is opening like azipper. The new spreading sections are somewhat unusual:
One new spreading section of the South American-Antarctic Ridge is not perpendicular to Conrad fault, violating the perpendicular pattern of alternating spreading ridges and transform faults generally seen on slowly spreading oceanic ridges.
The new part of the Southwest Indian Ridge is masked by the recently formed Spiess Seamount,[7] which is also known as Spiess Ridge,[9] and this means that it is not possible to classify the junction definitely as R-R-R as it may still be R-F-F transitioning to R-R-R,[7] being for the last 1 Ma ridge–fault–ridge, (R-F-R).[8] This volcanic seamount is now more than 2 million years old,[8] and is the highest point in the area after Bouvet Island. Spiess Seamount was named afterCaptainFritz Spieß [de] of theGerman Meteor expedition of 1926.[9]
Migdisova, NA; Sobolev, AV; Sushchevskaya, NM; Dubinin, EP; Kuz’min, DV (2017). "Mantle heterogeneity at the Bouvet triple junction based on the composition of olivine phenocrysts".Russian Geology and Geophysics.58 (11):1289–304.Bibcode:2017RuGG...58.1289M.doi:10.1016/j.rgg.2017.02.004.
Buikin, AI; Verchovsky, AB; Migdisova, NA (2018). "N–C–Ar–He isotopic systematics of quenched tholeiitic glasses from the Bouvet triple junction area".Geochemistry International.56 (13):1368–83.Bibcode:2018GeocI..56.1368B.doi:10.1134/S0016702918130037.
Sclater, J.G.; Bowin, C.; Hey, R.; Hoskins, H.; Peirce, J.; Phillips, J.; Tapscott, C. (1976). "The Bouvet triple junction".Journal of Geophysical Research.81 (11):1857–1869.Bibcode:1976JGR....81.1857S.doi:10.1029/JB081i011p01857.
Mitchell, N.C.; Livermore, R.A. (1998). "Spiess Ridge: An axial high on the slow spreading Southwest Indian Ridge".Journal of Geophysical Research: Solid Earth.103 (B7):15457–15471.Bibcode:1998JGR...10315457M.doi:10.1029/98JB00601.
