Marie Tharp: Seafloor mapping and ocean plate tectonics

The pioneering seafloor mapping and visualization 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.

Marie Tharp co-authored the first papers describing the major fracture zones in the Central Atlantic (Chain, Romanche, Vema), and her work directly contributed to the recognition of the role of mid-ocean ridges in plate tectonics and oceanic accretion.

Heezen &Tharp physiographic diagram of the North Atlantic, painted by H.C. Berann in 1968 And at Lamont in July 2001, after she received the Lamont- Doherty Heritage Award. Photo credit: Bruce Gilbert

Marie Tharp, July 30, 1920 (Ypsilanti, Michigan) in New York just after she was hired in Maurice Ewing’s lab at Lamont –August 23, 2006 (Nyack, New York). document: the 2019 GMRT grid. for the Azores region, and as a comparison, a 3D view over the same region using the most recent global bathymetric mapping detailed and probably more evocative than maps would have been. As an illustration we show their 1957 physiographic diagram look outdated, yet given the scarcity of actual bathymetric soundings Tharp and Heezen had to work with, they are remarkably Tharp and Heezen opted for physiographic diagrams instead of maps to represent their bathymetric compilations. These diagrams

1957 Heezen &Tharp physiographic diagram of the Azores region, Atlantic Ocean

2019 GMRT grid Version 3.7 Ryan, W.B.F. et al., 2009, Global Multi-Resolution Topography synthsis, Geochem. Geophys. Geosyst., 10, Q03014, doi: 10.1029/2008GC002332 Atlantis Seamount Mid-Atlantic Ridge Meteor Seamount which works well for most ridges in the area except the Southwest Indian). arrows next to the ridges and large black arrows on continents) are quite accurate (they assumed ridge-perpendicular displacement boundaries. The ridges are there, and properly identified as accommodating divergence. The proposed movements (small white interpretation of plate drift in the Northweastern part of this ocean, compared again with the 2019 GMRT grid with Bird (2003) plate One of Tharp and Heezen great achievements was mapping the seafloor in the Indian Ocean. In this sketch you see their 1965 1965 Heezen &Tharp, Tectonic fabric of the Atlantic and Indian oceans and continental drift

2019 GMRT grid Version 3.7 with plate boundaries by Bird, 2003 An updated digital model of plate boundaries, Geoch, Geol Geosystems, 10.1029/2001GC000252

Mapping melt-poor sections of ultraslow ridges to understand the impact of changes in magma supply on mid-ocean ridge tectonics

Figures from Cannat, Sauter et al., EPSL (2019).

TS6.4 Rift to ridge: the record of continental breakup processes Convener: Michael NirrengartenECS | Co- conveners: Julie TugendECS, J. Kim Welford, James NorcliffeECS, Craig Magee Displays | Chat Tue, 05 May, 14:00–18:00 nearly amagmatic spreading corridor at 64°E

The part of the plate divergence that is not accommodated by magma is taken up by normal faults with displacements up to 20 km that bring rocks all the way up from the mantle to the seafloor. nearly amagmatic spreading corridor at 64°E

The transition from tectonically-dominated (in nearly amagmatic corridor) to magmatically- dominated spreading occurs along axis within 35 km, melt emplacement taking over faulting as the principal means for plate separation.