Fracture zones are common features in the geology of oceanic basins. Globally most fault zones are located on divergent plate boundaries on oceanic crust. This means that they are located around mid-ocean ridges and trend perpendicular to them. The term fracture zone is used almost exclusively for features on oceanic crust; similar structures on continental crust are instead termed transform or strike slip faults. The term fracture zone has a distinct geological meaning, but it is also used more loosely in the naming of some oceanic features. Fracture zones are much longer than wide, but may have feature complexity within their width. Not all named fracture zones are active, indeed only the central portion of those still forming usually is, in an area of active transform faulting associated with a mid-ocean ridge. Classic fracture zones remain significant ocean floor features with usually different aged rocks on either side of the fracture zone due to past tectonic processes. Some fracture zones have been created by mid-ocean ridge segments that have been subducted and that part may no longer exist.
Most fracture zones in the Pacific Ocean originate from large mid-ocean ridges (also called "rises") such as the East Pacific Rise, Chile Rise and Juan de Fuca Ridge. The plates that host the fractures are Nazca, Pacific, Antarctic, Juan de Fuca and Cocos among others. Fracture zones being subducted under Southern and Central America are generally southwest-northeast oriented reflecting the relative motion of Cocos, Nazca and the Antarctic Plates.
The fracture zones of the Chile Rise trend in a west to east fashion with the most southern ones taking a slightly more southwest to northeast orientation. This non-perpendicular relation to Chile's coast reflects the oblique subduction of Nazca Plate under southern Chile. West of Chile rise the fracture zones are hosted in the Antarctic Plate. Some fracture zones such as Chile and Valdivia make up large sections of the Nazca-Antarctic Plate boundary.
| Name | Minimum length in km | Length of transform boundary in km | Position at Ridge[1] [2] | |
|---|---|---|---|---|
| 2250-1NaN-1 | 1100-1NaN-1 | -35.54°N -104.6175°W | ||
| 1750-1NaN-1 | 50-1NaN-1 | -42.9953°N -83.1847°W | ||
| 50-1NaN-1 | -45.9081°N -76.4253°W | |||
| 0 | ||||
| 0 | -49.1131°N -80.2092°W | |||
| 1550-1NaN-1 | 280-1NaN-1 | -44.7986°N -80.2647°W | ||
| 1300-1NaN-1 | 70-1NaN-1 | -45.7353°N -77.4589°W | ||
| 0 | ||||
| 450-1NaN-1 | 0 | -39.24°N -77.3831°W | ||
| 0 | ||||
| 0 | ||||
| 2100-1NaN-1 | 650-1NaN-1 | -41.3903°N -87.3933°W |
The East Pacific Rise includes the Pacific-Antarctic Rise (Pacific Plate and Antarctic Plate boundary) in some usages and in others relates only to the boundaries between the Pacific Plate and the Nazca Plates which includes the Juan Fernández Plate and Easter Microplate.
| Name | Minimum length in km | Length as plate boundary in km | Coordinates | |
|---|---|---|---|---|
| 0 | ||||
| 0 | -19.8244°N -77.5981°W | |||
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| 0 | ||||
| 0 | ||||
| 0 | ||||
| 0 | ||||
| 0 | ||||
| 0 | ||||
| 0 | ||||
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Some of the fracture zones in the western Pacific Ocean are associated with the smaller plate boundaries of the active back-arc basin spreading center of the North Fiji Basin being the Hunter Fracture Zone and North Fiji Fracture Zone. The Parece Vela Rift (Parece Vela Fracture Zone Province) is also associated with the back-arc basin of the Parece Vela Basin (West Mariana Basin) at the intersection of the Philippine Sea Plate and Mariana Plate.[3]
(some are inactive)[4]
Surveyor, Molokai, Pioneer and Murray fracture zones shown in the list were created by ridge segments that no longer exist.[4]
In the Atlantic Ocean most fracture zones originate from the Mid-Atlantic Ridge, which runs from north to south, and are therefore west to east oriented in general. There are about 300 fracture zones, with an average north-south separation of 55km (34miles):[5] two for each degree of latitude. Physically it makes sense to group Atlantic fracture zones into three categories:
| American side | African side | |
|---|---|---|
| Hudson Fracture Zone | ||
| Snorri Fracture Zone | ||
| Cartwright Fracture Zone | ||
| Julian Haab Fracture Zone | ||
| Minna Fracture Zone | ||
| Leif Fracture Zone | ||
| Newfoundland Fracture Zone[11] | ||
| Kelvin Fracture Zone[12] | Canary Fracture Zone | |
| Cape Fear Fracture Zone | Cape Verde Fracture Zone | |
| Bahama Fracture Zone | Guinea Fracture Zone |
| Name | Minimum length in km | Length of transform fault in km | Position at Ridge | |
|---|---|---|---|---|
| 2445 | 950 | -0.49°N -20.49°W | ||
| Chain Fracture Zone | 1315 | 269 | -1.213°N -14.229°W | |
| Ascension Fracture Zone | 1149 | 264 | -6.928°N -12.283°W | |
| Bode Verde Fracture Zone | 3018 | 232 | -11.686°N -13.936°W | |
| Cardno Fracture Zone | 1649 | 87 | -14.076°N -14.056°W | |
| Tetyaev Fracture Zone | 810 | 122 | -16.271°N -13.719°W | |
| Saint Helena Fracture Zone | 1184 | 19 | -16.617°N -14.344°W | |
| Hotspur Fracture Zone | 1446 | 113 | -17.721°N -13.329°W | |
| Martin Vaz Fracture Zone | 1324 | 26 | -18.594°N -12.633°W | |
| Rio Grande Fracture Zone | 1774 | 156 | -29.081°N -13.067°W | |
| Tristan Da Cunha Fracture Zone | 1014 | 26 | -38.388°N -16.796°W | |
| Gough Fracture Zone | 1057 | 42 | -40.637°N -16.637°W | |
| Conrad Fracture Zone (to the west) | 316 | 0 | -55.185°N -0.133°W | |
| Bouvet Fracture Zone (to the east) | 198 | 0 | -55.185°N -0.133°W |
The Indian Ocean fracture zones are mainly related to the Southwest Indian Ridge and Southeast Indian Ridge mid-ocean ridges.
