Ages of St. Helena & Tristan Hotspot Systems

John O'Connor

Faculty of Earth Sciences, Vrije University Amsterdam


Age-progression along seamount chains and aseismic ridges, the observation leading to the birth of the mantle plume paradigm, remains unexplained some thirty years later. Active hotspots and their interactions with spreading ridges are the focus of numerous investigations. However, this approach provides only instantaneous glimpses of hotspot melting anomalies and their inferred underlying mantle plumes. Seamount chains and aseismic ridges have the advantage of providing long-term records of hotspot melting anomalies, more likely to reveal evidence for the existence – or otherwise – of a long-lived dynamic process characteristic of deep mantle plumes. Thus, detailed age and geochemical records of hotspot trails such as St. Helena and Tristan – especially as they are associated with continental breakup, volcanic margins and LIPs – could well prove to be one of the best ways of testing competing hypotheses for the origin of hotspot melting anomalies. Although time-progression has been established for the St. Helena and Tristan trails [1-3], a sufficiently detailed age/geochemical record is lacking for volcanism trailing from young ocean islands to continental margins and, in the case of Tristan, into continental flood basalts. While acquiring sufficient information about the history and distribution of S. Atlantic hotspot volcanism would be challenging, it is likely to lead to more rigorous testing of the mantle plume paradigm.

[1] O'Connor, J.M., P. Stoffers, P. van den Bogaard, and M. McWilliams, First seamount age evidence for significantly slower African plate motion since 19 to 30 Ma, Earth Planet Sci. Lett., 171, 575-589, 1999.
[2] O'Connor, J.M., and A.P. Le Roex, South Atlantic Hot Spot - Plume Volcanism: 1. Distribution of volcanism in time and space, Earth and Planet. Sci. Lett., 113, 343-364, 1992.
[3] O'Connor, J.M., and R.A. Duncan, Evolution of the Walvis Ridge and Rio Grande Rise hot spot system: Implications for African and South American plate motions over plumes, J. Geophys. Res., 95, 17, 475-17, 502, 1991.