Electron microprobe characterization of ash layers in sediments from the central Bransfield basin (Antarctic Peninsula): evidence for at least two volcanic sources
Bransfield Strait, a narrow active rift with three submarine basins, separates the South Shetland Islands from northern Antarctic Peninsula. Volcanism in Bransfield Strait commenced prior to 0.75 Ma and continues, with recent subaerial eruptions at Deception, Bridgeman and Penguin islands, submarine hydrothermal activity and numerous young basaltic seamounts located along the rift axis. Gravity cores were collected from five locations within the central Bransfield basin. Diatomaceous mud interbedded with terrigenous detritus and discrete ash layers up to 10 cm thick are the commonest sediment types in all the cores. The major element compositions of glass shards within the ash layers are, apart from the uppermost layer, compositionally similar to pyroclastic units preserved on Deception Island, a young (<0.75 Ma) active stratovolcano. The uppermost ash layer cannot be closely matched compositionally to any known source in the Antarctic–Scotia Sea–southern South America region. Its presence indicates that a volcanic centre other than Deception Island contributed ash to the Bransfield basin. Based on the shallow stratigraphical position of the compositionally distinctive ash layer, only a few decimetres beneath the seafloor, its source volcano was probably active in historical times (<few hundred years).(Received January 14 2002)
(Accepted August 19 2002)
Key Words: ash layers; Bransfield Strait; Deception Island; geochemistry.