3-D magnetotelluric image of offshore magmatism at the Walvis Ridge and rift basin

Marion Jegen, Anna Avdeeva, Christian Berndt, Gesa Franz, Björn Heincke, Sebastian Hölz, Anne Neska, Anna Marti, Lars Planert, J. Chen, Heidrun Kopp, Kiyoshi Baba, Oliver Ritter, Ute Weckmann, Naser Meqbel, Jan Behrmann

Research output: Contribution to journalArticleResearchpeer-review

11 Citations (Scopus)

Abstract

The Namibian continental margin marks the starting point of the Tristan da Cunha hotspot trail, the Walvis Ridge. This section of the volcanic southwestern African margin is therefore ideal to study the interaction of hotspot volcanism and rifting, which occurred in the late Jurassic/early Cretaceous. Offshore magnetotelluric data image electromagnetically the landfall of Walvis Ridge. Two large-scale high resistivity anomalies in the 3-D resistivity model indicate old magmatic intrusions related to hot-spot volcanism and rifting. The large-scale resistivity anomalies correlate with seismically identified lower crustal high velocity anomalies attributed to magmatic underplating along 2-D offshore seismic profiles. One of the high resistivity anomalies (above 500 Ωm) has three arms of approximately 100 km width and 300 km to 400 km length at 120° angles in the lower crust. One of the arms stretches underneath Walvis Ridge. The shape is suggestive of crustal extension due to local uplift. It might indicate the location where the hot-spot impinged on the crust prior to rifting. A second, smaller anomaly of 50 km width underneath the continent ocean boundary may be attributed to magma ascent during rifting. We attribute a low resistivity anomaly east of the continent ocean boundary and south of Walvis Ridge to the presence of a rift basin that formed prior to the rifting.

Original languageEnglish
Pages (from-to)98-108
Number of pages11
JournalTectonophysics
Volume683
DOIs
Publication statusPublished - 30 Jun 2016
Externally publishedYes

Keywords

  • Hotspot
  • Magmatic intrusions
  • Marine magnetotellurics
  • Passive margins
  • Tristan da Cunha
  • Walvis Ridge

Programme Area

  • Programme Area 4: Mineral Resources

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