EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Geological mapping in the offshore domain: unravelling the tectonic history of the Scotia Sea

Anouk Beniest1,2 and Wouter P. Schellart1
Anouk Beniest and Wouter P. Schellart
  • 1Vrije Universiteit Amsterdam, Faculty of Science, Earth Sciences, Amsterdam, Netherlands (
  • 2GEOMAR, Helmholtz-Zentrum für Ozeanforschung, Kiel, Germany

We produced the first geological map of the Scotia Sea area based on the available geophysical and geological data. Combining magnetic, Bouguer gravity anomaly and high-resolution bathymetric data with geological data from dredged samples allowed us to map lithologies and structural features in this mostly submerged and complex tectonic area. This geological map allowed us to integrate a very inter-disciplinary dataset, thereby reviewing the available data and addressing some of the still persisting geological challenges and controversies in the area.

One of the most important and persistent discussions is the nature and age of the Central Scotia Sea. We mapped this part of the Scotia Sea as basaltic-andesitic lithology partly covered by thick, oceanic sediments. This differs in lithology from the West and East Scotia Sea, which we mapped as a basaltic lithology. Based on our lithological map, its unusual thickness and the presence of the Ancestral South Sandwich Arc (ASSA, early Oligocene-late Miocene) we argue that Central Scotia Sea has an Eocene to earliest Oligocene age.

Cross-sections combining the geology, crustal structure and mantle tomography reveal high velocity anomalies and colder mantle material below the structural highs along the South Scotia Ridge (Terror Rise, Pirie Bank, Bruce Bank and Discovery Bank) and below the South Sandwich Islands. We interpreted those as the southern, stagnated part of the subducting slab of the South Sandwich Trench, following the geometry of Jane Basin and the currently active subducting slab at the South Sandwich Trench. Low velocity anomalies are observed below Drake Passage and the East Scotia Sea, which are interpreted as warmer toroidal mantle flow around the slab edges below the Chilean trench and the South Sandwich trench.

Based on our geological map and integrated cross-sections we propose a multi-phase evolution of the Scotia Sea area with Eocene or older oceanic crust for the Central Scotia Sea. A first wide-rift-phase initiated before 30 Ma in the West Scotia Ridge, Protector Basin, Dove Basin and Jane Basin either as a result of the diverging South American and Antarctic continents and/or due to subduction rollback that commenced soon after subduction initiation that eventually caused the ASSA to form. The first full spreading center developed in the West Scotia Sea, aided by the warmer toroidal mantle flow causing spreading to be abandoned in the other basins (~30 Ma). A second rift phase in the fore-arc, in between the ASSA and the South Sandwich trench (~20 Ma), initiated through a redistribution of far-field forces as a result of continuous trench retreat. The warmer toroidal mantle concentrated on the East Scotia Ridge resulting in the second spreading system (15 Ma), abandoning the West Scotia Ridge spreading system 6-10 Ma.

We show that it is possible to create a geological map in a very remote area with an extreme environment with the available geological and geophysical data. This new way of producing geological maps in the offshore domain provides a better insight into the geological history of geologically complex areas that are largely submerged.

How to cite: Beniest, A. and Schellart, W. P.: Geological mapping in the offshore domain: unravelling the tectonic history of the Scotia Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2083,, 2020

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Display material version 1 – uploaded on 17 Apr 2020
  • CC1: Comment on EGU2020-2083, Annique van der Boon, 17 Apr 2020

    What a nice presentation, I really like the interactive format, and great easter egg!

  • CC2: Comment on EGU2020-2083, Gabriella Alodia, 07 May 2020

    Hi Anouk!

    I really like your map and curious about your method. Have you got a published paper or some sort in which I could have a look at it in more details? Thanks!

    • AC1: Reply to CC2, Anouk Beniest, 07 May 2020

      Hey Gabriella, Thanks for asking! It is not publisjed yet! It has been submitted and currently under review. I mapped the area manually. I loaded all georeferenced geophysical data files into QGIS, so this includes, bathymetry, magnetic data and Bouguer gravity anomaly and then I also plotted the locations of heat flow measurements and rock sample locations (dredged and cored) to get an idea about what geophysical signature would correspond with certain rock types. I also looked at seismic line and bathymetry to identify areas with a thick sediment cover, because that lowers the Bouguer gravity anomaly signal and may also weaken the magnetic signal. And then I started colouring. The rock samples were really useful, they were my tie-points to the geophysical signal.