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

Thursday, 18 December 2014
Susan Schnur, Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States, Anthony A P Koppers, Oregon State University, College of Earth, Ocean, and Atmospheric Science, Corvallis, OR, United States, Cornelia Class, Lamont -Doherty Earth Observatory, Palisades, NY, United States and William W Sager, University of Houston, Earth and Atmospheric Sciences, Houston, TX, United States
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.