EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Marie Tharp: Seafloor mapping and ocean plate tectonics

Mathilde Cannat, Deborah Smith, Daniel Fornari, Vicki Ferrini, and Javier Escartin
Mathilde Cannat et al.
  • Institut de Physique du Globe de Paris, Marine Geosciences, Paris, France (

The pioneering seafloor mapping by Marie Tharp played a key role in the acceptance of the plate tectonic theory. Her physiographic maps,  published with Bruce Heezen,  covered the Earth’s oceans and revealed with astonishing accuracy the submarine landscape. She exposed the full extent of the global mid-ocean ridge system, documented features such as seamounts and volcanic chains, trenches, and transform faults. Marie Tharp co-authored the first papers describing the major fracture zones in the Central Atlantic (Chain, Romanche, Vema). In 1952, she also discovered that the Atlantic ridge has a central valley (the axial valley), and convinced her colleague Bruce Heezen that it, which corresponds to sustained seismicity (highlighted by other researchers at the same time thanks to the worldwide networking of seismological stations), is a rift that separates the eastern and western provinces of the Atlantic Ocean. Tharp and Heezen were not yet talking about plate tectonics at this time. But when, at the beginning of the 1960s, the first magnetic anomaly maps showed that the oceans were "young", and that the age of the seabed increased with the distance from the ridges, their physiographic map became an essential element in understanding the role that these ridges play, as well as the distribution of the main current terrestrial plates. In this poster, we present original maps and sketches that document this key contribution to the understanding of the Earth's tectonics.

How to cite: Cannat, M., Smith, D., Fornari, D., Ferrini, V., and Escartin, J.: Marie Tharp: Seafloor mapping and ocean plate tectonics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12641,, 2020

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  • CC1: Comment on EGU2020-12641, William Ryan, 06 May 2020

    Thank you for your generous recognition of Marie Tharp's impact on Plate Tectonics. I was in the office next to hers when she was working on the Inian Ocean physiograpic diagram in 1963-1965.  I remember her map (attached) showing opposite offsets of the Owen Fracture Zone in the north and offsets on the SW Indian Ocean Ridge. I remember her discussing with Bruce Heezen and the other grad students that if Africa was stationary, this requied India and Antarctic to have drifted away from each other. That then requied three mid-ocean ridge rift valleys joined together at what we call a triple junctiion. She sketched this on her white globe and from her mathamatics background she explained this could be explained by rotations around separate Euler Poles. What a shame that she and Bruce never published this concept and it is only evident in her attached map.


    Bill Ryan

    • AC1: Reply to CC1, Mathilde Cannat, 13 May 2020

      dear Bill, thanks you for this insight into M. Tharp's contribution! 

      It is indeed a pity this Euler pole interpretation was not published at the time... From your witness account it seems that Marie was an active proponent of bold scientific ideas... how do you explain she was never the first author of a paper? 

      And did you witness Tharp and Heezen discussing the Plate tectonics theory at this crucial 1963-1965 period?

      Also the map you show here is different from the one I copied in my presentation, from Heezen and Tharp's  1965 Indian Ocean paper.... and it looks better in that it appears to have the N-S opening direction right for the southwest indian ridge.. in the 1965 paper the sketch has ridge perpendicular displacements everywhere... Where (if) was the map you show published? and do you understand why it differs from that in the 1965 paper?


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