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WALVIS I: Ar/Ar Geochronology and Geochemistry of existing samples from the Walvis Track and Rio Grande Rise.

Principal Investigators: Prof. Dr. Kaj Hoernle, Dr. Folkmar Hauff, Dr. Reinhard Werner

An integrated Ar/Ar geochronological and geochemical study (major and trace element and Sr-Nd-Pb- Hf-O isotopes) is carried out on existing samples from the Walvis Track and Rio Grande Rise. This data is fundamental to evaluate plume head / plume tail versus plate fracturing models for the origin of HoernleRundeIIthese massive volcanic structures which are commonly believed to reflect a mantle-plume-related hotspot track connecting the Etendeka Flood Basalts with Tristan and Gough Islands. In addition, the Walvis Ridge is considered a type locality for the enriched mantle (EM) I endmember of intraplate basalts. Our sample collection comprises >100 samples from 34 sites of various international cruises and from five DSDP sites. Preliminary data of this project on samples from the Gough and Traistan seamount chains indicate a longterm, most likely vertical zonation of the mantle source. A first set of samples for age dating is presently underway. Overall the projects aims to test for age progressive magmatism along the Walvis Track, to evaluate changes in chemical composition through time, particularly to see if there is a geochemical zonation along this volcanic lineament, and to constrain further the ultimate origin of the EM-I mantle endmember. This study serves as the basis for a more detailed survey along the Walvis Ridge with R/V Meteor / Merian in 2011.