New Rb-Sr mineral ages temporally link plume events with accretion at the margin of Gondwana

Five of six Rb-Sr muscovite mineral isochron ages from the Scotia Metamorphic Complex of the South
Orkney Islands, West Antarctica, average 190 ± 4 Ma. The muscovite ages are interpreted to date foliation-formation
and thus also accretion and subduction at the Gondwana margin. Coincident picrite and ferropicrite magmatism,
indicative of melts from deep-seated depleted mantle, permits a causative link between accretion and the arrival of the
Karoo – Ferrar – Chon Aike mantle plume in the Early Jurassic. Three biotite Rb-Sr mineral isochron ages are
consistently younger and average 176 ± 5 Ma. The biotite ages may record post-metamorphic cooling or more likely
retrogressive metamorphic effects during uplift.