Petrography, Major and Trace Element Geochemistry of the Discovery Seamounts

• Main Author: Hoffmann, Paulina Ewa
• Format: Thesis
• Language: English
• Published: 2012
• Subjects: Course of study: MSc Geoscience; South Atlantic Ocean; Ocean Island
• Online Access: https://oceanrep.geomar.de/id/eprint/19931/; https://oceanrep.geomar.de/id/eprint/19931/1/HoffmannMasters1012.pdf

The Discovery Seamounts form a major bathymetric high in the South Atlantic southwestern of South Africa. Until now the seamounts were poorly explored: in two expeditions only five dredges could recover volcanic material from the seafloor. During the cruise MSM 19/3 with R/V Maria S. Merian in December 2011 ten more dredges recovered volcanic material from the seamounts. These samples were petrographically examined and analyzed for major and trace element contents (XRF and ICP-MS). Due to advanced stages of alteration, some of the newly obtained samples are both richer in secondary volatile and P2O5 contents than the previously described samples. The most evolved lavas occur in the northeast (trachybasalts, basaltic trachyandesites, trachyandesites and trachytes), whereas the southwestern part of the Discovery Seamounts is dominated by more primitive lavas with basanitic/tephritic and basaltic compositions. The samples are all alkaline in character, were erupted in an intraplate setting and show a highly enriched OIB-like trace element pattern. Some trace elements even show higher values than other South Atlantic ocean island basalts. The Discovery Seamounts lie within the belt of the Dupal anomaly, whose origin is still a controversy. Different hypotheses on the origin of these anomalous enriched lavas have been published, including the presence of the Discovery Plume causing the enrichment of the magma source region. The enrichment in specific trace elements indicates that the EM1-mantle endmember as a possible source of the magma source region. The new data contribute to an improved understanding of the petrogenesis and geochemistry of the Discovery Seamounts.