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 either side of an active transform fault move in opposite directions; here, strike-slip activity occurs. Fracture zones extend past the transform faults, away from the ridge axis; are usually seismically inactive (because both plate segments are moving in the same direction), although they can display evidence of transform fault activity, primarily in the different ages of the crust on opposite sides of the zone.
21-514: The Easter Fracture Zone is an oceanic fracture zone associated with the transform fault extending from the Tuamotu archipelago in the west to the Peru–Chile Trench to the east. The Easter Fracture Zone extends roughly 5900 kilometers from 20°S,131°W to 26°S,78°W. The landscape consists of several ridges and isolated volcanos with maximal peak elevation above the seafloor of 3000m. Because
42-531: A "Subsea Berlin Wall" segregating the North Atlantic communities from those in other oceans. Swarms of hydrothermal shrimps reminiscent of those found from northern MAR vent-sites have been found on the northern part of the southern MAR. Bivalve communities have been reported around vents further south. These species await a formal description, and it is not known whether they represent communities distinct from those on
63-546: A total of 350 km to the west. The section of the Mid-Atlantic Ridge between the two fracture zones is seismically active. The flow of major North Atlantic currents is associated with this fracture zone which hosts a diverse deep water ecosystem. The Heirtzler Fracture Zone was approved by the Advisory Committee on Undersea Features in 1993. The Mendocino Fracture Zone extends for over 4,000 km off
84-848: Is 125 km long and 15 km wide. Romanche Trench The Romanche Trench , also called the Romanche Furrow or Romanche Gap , is the third-deepest of the major trenches of the Atlantic Ocean , after the Puerto Rico Trench and the South Sandwich Trench . It bisects the Mid-Atlantic Ridge (MAR) just north of the equator at the narrowest part of the Atlantic between Brazil and West Africa, extending from 2°N to 2°S and from 16°W to 20°W. The trench has been formed by
105-723: Is constrained by numerous obstacles on the seafloor. In the basin on the eastern side of the MAR the Walvis Ridge blocks the northward passage. For LNADW and AABW, the Romanche and Chain Fracture Zones (just south of the equator) are the only deep passages in the MAR where interbasin exchange is possible. As AABW flows through the Romanche Fracture Zone, salinity and temperature increase significantly. The Romanche Fracture Zone offsets
126-561: Is found around 3,600–4,000 metres (11,800–13,100 ft) below sea level and flows from the Greenland and Norwegian seas; it brings high salinity, oxygen, and freon concentrations towards the equator. Antarctic Bottom Water (AABW) flows below the LNADW and reaches down to the seafloor. Formed around Antarctica, the AABW is cold, has low salinity, and high silicate concentration. As it flows north, it
147-508: The Juan de Fuca Ridge and the Gorda Ridge . The dominating feature of the fracture zone is the 150 km long Blanco Ridge, which is a high-angle, right-lateral strike slip fault with some component of dip-slip faulting . The Charlie-Gibbs Fracture Zone consists of two fracture zones in the North Atlantic that extend for over 2000 km. These fracture zones displace the Mid-Atlantic Ridge
168-654: The Romanche Trench , this fracture zone separates the North Atlantic and South Atlantic oceans. The trench reaches 7,758 m deep, is 300 km long, and has a width of 19 km. The fracture zone offsets the Mid-Atlantic Ridge by more than 640 km. The Sovanco Fracture Zone is a dextral-slip transform fault running between the Juan de Fuca and Explorer Ridge in the North Pacific Ocean . The fracture zone
189-511: The MAB of the South Atlantic. The western part of the transverse ridge consists of fragments of uplifted oceanic crust and upper mantle . The summit of the transverse ridge is capped by Miocene shallow-water limestones that reached above sea level 20 Ma before subsiding abnormally fast. The eastern part of the transverse ridge, however, consists of a thick sequence of stratified material called
210-490: The Mid-Atlantic ridge by 900 km (560 mi), making it the largest equatorial fracture zone in the Atlantic. According to the normal scenario for the opening of the South Atlantic , it is spreading at a rate of 1.75 cm/year (0.69 in/year) and began forming about 50 Ma . North of and parallel to the fracture zone is a transverse ridge which is particularly prominent over hundreds of kilometers east and west of
231-537: The Romanche Sedimentary Sequence (RSS). The RSS includes pelagic material from the early Cretaceous (140 Ma) which, coupled with the thickness of the sequence, does not fit with the normal scenario for the opening of the South Atlantic around the Aptian - Albian (125–100 Ma). The transverse ridge separates the present trench from an 800 km (500 mi)-long aseismic valley where the Romanche transform
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#1732844892117252-612: The actions of the Romanche Fracture Zone , a portion of which is an active transform boundary offsetting sections of the Mid-Atlantic Ridge. It was named after the French navy ship La Romanche , commanded by captain Louis-Ferdinand Martial which on 11 October 1883 made soundings that revealed the trench. The boat was returning to France after spending a few months on a scientific mission near Cape Horn as part of
273-448: The coast of California and separates the Pacific plate and Gorda plate . The bathymetric depths on the north side of the fracture zone are 800 to 1,200 m shallower than to the south, suggesting the seafloor north of the ridge to be younger. Geologic evidence backs this up, as rocks were found to be 23 to 27 million years younger north of the ridge than to the south. Also known as
294-480: The first International Polar Year . The trench has a depth of 7,761 m (25,463 ft), is 300 km (190 mi) long, has an average width of 19 km (12 mi), and allows for a major circulation of deep-ocean-basin water from the west Atlantic to the east Atlantic basins. Deep water flow through the trench is from west to east with a rate of 3.6 Sverdrups (million m³/s) of 1.57 °C (34.83 °F) water. Lower North Atlantic Deep Water (LNADW)
315-814: The local seafloor has depths around 4000m to the north of the fracture zone and 3400m to the south of the fracture zone, most of its volcanic peaks form seamounts . They do rise above sea level at the Pitcairn Islands and Easter Island . This tectonics article is a stub . You can help Misplaced Pages by expanding it . Fracture zone In actual usage, many transform faults aligned with fracture zones are often loosely referred to as "fracture zones" although technically, they are not. They can be associated with other tectonic features and may be subducted or distorted by later tectonic activity. They are usually defined with bathymetric , gravity and magnetic studies. Mid-ocean ridges are divergent plate boundaries. As
336-451: The northern MAR. The flow of NADW through the Romanche and Chain Fracture Zones may serve as a conduit for larval transport from the western North Atlantic to the eastern South Atlantic. For example, the caridean shrimp Alvinocaris muricola inhabits cold seeps in both the Gulf of Mexico and the Gulf of Guinea , which clearly suggests a gene flow across the Atlantic, but the amount of data
357-406: The offset in the magnetic striping, one can then determine the rate of past plate motions. In a similar method, one can use the relative ages of the seafloor on either side of a fracture zone to determine the rate of past plate motions. By comparing how offset similarly aged seafloor is, one can determine how quickly the plate has moved. The Blanco Fracture Zone is a fracture zone running between
378-409: The plates on either side of an offset mid-ocean ridge move, a transform fault forms at the offset between the two ridges. Fracture zones and the transform faults that form them are separate but related features. Transform faults are plate boundaries, meaning that on either side of the fault is a different plate. In contrast, outside of the ridge-ridge transform fault, the crust on both sides belongs to
399-408: The same plate, and there is no relative motion along the junction. The fracture zone is thus the junction between oceanic crustal regions of different ages. Because younger crust is generally higher due to increased thermal buoyancy , the fracture zone is characterized by an offset in elevation with an intervening canyon that may be topographically distinct for hundreds or thousands of kilometers on
420-479: The sea floor. As many areas of the ocean floor, particularly the Atlantic Ocean, are currently inactive, it can be difficult to find past plate motion. However, by observing the fracture zones, one can determine both the direction and rate of past plate motion. This is found by observing the patterns of magnetic striping on the ocean floor (a result of the reversals of Earth's magnetic field over time). By measuring
441-467: Was located until about 10–8 Ma. This transform migration was preceded by a process 25–17 Ma during which the Miocene shallow-water platform mentioned above reached sea level as the transverse ridge was first uplifted , then deformed, and finally buried under the sea. The hydrothermal vents of the MAR support many life forms. The Romanche and Chain Fracture Zones create a huge gap in the MAR and can act as
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