$Vemafracturezone-qgis$ Vematransform

The Vema Fracture Zone is a

fracture zone A fracture zone is a linear feature on the ocean floor—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on eit ...

in the equatorial

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

. It offsets the

Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North Ame ...

by 320 km to the left. Its transform valley has a depth of 5000m. The fracture zone can be traced for over 2500 km east to west.

Exploration history

From temperature data gathered from the deep ocean on the

German Meteor expedition The German Meteor expedition (German: ''Deutsche Atlantik Expedition'') was an oceanographic expedition that explored the South Atlantic ocean from the equatorial region to Antarctica in 1925–1927. Depth soundings, water temperature studies, wat ...

(1925-1927) Georg Wüst already suspected that there should be a passage through the Mid-Atlantic Ridge around

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

9 North. The Vema Fracture Zone was then discovered in 1956 by G.R. Hamilton on board , with additional surveying taking place in the years 1959–1960. In the 1960s research was done by , , RV Chain, RV Argo and . The fault was subsequently explored by the French research vessel Jean Charcot in 1977 using its SeaBeam Classic

multibeam echosounder A multibeam echosounder (MBES) is a type of sonar that is used to map the seabed. It emits acoustic waves in a fan shape beneath its transceiver. The time it takes for the sound waves to reflect off the seabed and return to the receiver is used ...

, the French

submersible A submersible is a small watercraft designed to operate underwater. The term "submersible" is often used to differentiate from other underwater vessels known as submarines, in that a submarine is a fully self-sufficient craft, capable of ind ...

Nautile ''Nautile'' is a crewed submersible owned by Ifremer, the French Research Institute for Exploitation of the Sea. Commissioned in 1984, the submersible can be operated at depths of up to . ''Nautile'' is capable of housing three people. It has a ...

and its

mothership A mother ship, mothership or mother-ship is a large vehicle that leads, serves, or carries other smaller vehicles. A mother ship may be a maritime ship, aircraft, or spacecraft. Examples include bombers converted to carry experimental airc ...

RV Nadir in 1989, the US {{ship, RV, Maurice Ewing in 1993, and the Russian RV Akademik Nikolay Strakhov in 1998, making it one of the world's best surveyed seafloor features.

Transverse ridge

The southern wall of the transform valley is crowned by one of the longest and highest transverse

ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...

s of the entire

mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverge ...

system. This narrow ridge must have risen as a single vertical slab 6.6 million years ago. Up to three million years ago the ridge was at or even above

sealevel Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...

. Later it subsided to its present depth of 450 meters.

Lema Fracture Zone

While the transform valley of the Vema Fracture Zone has a V-shaped profile, the next fracture zone to the south has a steep vertical wall on its southern side rising from a horizontal valley bottom. As an L would fit in well here, this fracture zone is nicknamed Lema Fracture Zone. The north–south distance between the Vema and Lema fracture zones is 70 km.

Ridge jump

Up to 2.2 million years ago the Vema transform fault was 40 km shorter than today, and the Lema fracture zone had a leftward offset of 40 km. Then the old spreading valley between Lema and Vema died, and spreading started from an axis 40 km to the east. The Vema transform was thus extended by 40 km, while the Lema fracture zone was reduced to zero offset. Spreading from the new axis has meanwhile increased the distance between the old and the new axis to 80 km.

Notes

Fracture zones Mid-Atlantic Ridge