Explaining Tristan-Gough Plume Dynamics with New Age Data from Multiple Age-Progressive Seamount Sub-Tracks in the Young Walvis Ridge Guyot Province

Abstract:

Together, the Etendeka flood basalt province of Namibia, the old Walvis Ridge and the young Walvis Ridge guyot province constitute a 130 Myr record of hotspot volcanism in the South Atlantic. Previous age-dating along the Walvis Ridge has revealed a strong linear age progression (~30 mm/a, Rohde et al. 2013) that is consistent with modeled relative spreading rates between the African and South American plates (~33 mm/a over the past 3 Myr, NUVEL-1 model). However, tracing the path of the African plate over the Tristan-Gough hotspot is more complicated in the guyot province because the seamounts do not form a single trail. Instead we see a region of diffuse volcanism with multiple discontinuous linear sub-tracks of seamounts and coeval volcanism at edifices located up to 400 km apart. We present here the results of 24 new ⁴⁰Ar/³⁹Ar step-heating experiments on groundmass and phenocryst separates from trachybasalts, trachy-andesites, trachytes and similarly evolved rocks dredged from the guyot province in 2012. The age-dating results represent nine seamounts in the southern half of the guyot province, most of which have never been studied before. We will combine the new ages with previous high-resolution ages from nearby seamounts to constrain plate motion rates recorded by each of the sub-tracks. We will compare the results with previously-established absolute plate motion models in order to shed light on the relationship between plume dynamics and the unusual spatial distribution of volcanism in this region.