Hubbry Logo
Fracture zoneFracture zoneMain
Open search
Fracture zone
Community hub
Fracture zone
logo
7 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Fracture zone
Fracture zone
Fracture zone
View on Wikipedia
from Wikipedia
Map
Approximate surface projection on oceans of named fracture zones (orange). Also shown are relevant present plate boundaries (white) and associated features (lighter orange). Click to expand to interactive map.[1]

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.

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.

Structure and formation

[edit]

Mid-ocean ridges are divergent plate boundaries. As the plates on either side of an offset mid-ocean ridge move, a transform fault forms at the offset between the two ridges.[2]

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 the same plate, and there is no relative motion along the junction.[3] 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 the sea floor.

Geologic importance

[edit]
Blanco fracture zone map
Bathymetry map of the North Atlantic Ocean showing the full extent of the Charlie-Gibbs fracture zone (horizontal black lines in the center of the image)
Magnetostratigraphy of the East Pacific Rise near the Heirtzler fracture zone showing ages of sea floor spreading in millions of years (Ma)
The Romanche fracture zone with red arrows indicating directions of movements of tectonic plates

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 the offset in the magnetic striping, one can then determine the rate of past plate motions.[4] 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.[3]

Examples

[edit]
Main article: List of fracture zones

Blanco fracture zone

[edit]

The Blanco fracture zone is a fracture zone running between the Juan de Fuca Ridge and the Gorda Ridge. The dominating feature of the fracture zone is the 150 km (93 mi) long Blanco Ridge, which is a high-angle, right-lateral strike slip fault with some component of dip-slip faulting.[5]

Charlie-Gibbs fracture zone

[edit]

The Charlie-Gibbs fracture zone consists of two fracture zones in the North Atlantic that extend for over 2,000 km (1,200 mi). These fracture zones displace the Mid-Atlantic Ridge a total of 350 km (220 mi) to the west. The section of the Mid-Atlantic Ridge between the two fracture zones is seismically active.[6] The flow of major North Atlantic currents is associated with this fracture zone which hosts a diverse deep water ecosystem.[7]: 3 

Heirtzler fracture zone

[edit]

The Heirtzler fracture zone was named after James Ransom Heirtzler, who first demonstrated through magnetostratigraphy that the Mid-Atlantic Ridge was spreading south of Iceland, providing the first clear evidence for plate tectonics.[8] This name was approved by the Advisory Committee on Undersea Features in 1993.[9] The area around the Heirtzler fracture zone and the Pacific–Antarctic Ridge which is a southwestern portion of the East Pacific Rise has been mapped in detail by amongst other techniques magnetostratigraphy (see picture on this page).[10]

Mendocino fracture zone

[edit]

The Mendocino fracture zone extends for over 4,000 km (2,500 mi) off 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 (2,600 to 3,900 ft) 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.[11]

Romanche fracture zone

[edit]

Also known as the Romanche Trench, this fracture zone separates the North Atlantic and South Atlantic oceans. The trench reaches 7,758 m (25,453 ft) deep, is 300 km (190 mi) long, and has a width of 19 km (12 mi). The fracture zone offsets the Mid-Atlantic Ridge by more than 640 km (400 mi).[12]

Sovanco fracture zone

[edit]

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 is 125 km (78 mi) long and 15 km (9.3 mi) wide.[13]

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Fracture zone

View on Grokipedia
from Grokipedia
A fracture zone is a linear feature on the ocean floor, typically extending hundreds to thousands of kilometers, characterized by irregular formed by a series of fractures, faults, and ridges that represent the inactive extensions of transform faults beyond active segments. These zones are prominent scars in the oceanic lithosphere, resulting from the offset of spreading centers during . Fracture zones form as part of the process at mid-ocean ridges, where accommodate lateral offsets between adjacent ridge segments, allowing plates to slide past one another. As new is generated at the ridge axis, the active becomes inactive away from the ridge, evolving into a fracture zone that preserves the topographic and structural signature of past faulting. Unlike active , fracture zones in plate interiors exhibit no ongoing tectonic motion but often display graben-like structures indicative of crustal extension and subsequent thermal contraction as the cools with age. These features play a significant role in oceanic and , influencing deep-sea currents by channeling nutrient-rich waters and supporting diverse benthic communities, as seen in zones like the Charlie-Gibbs Fracture Zone, which spans about 2,000 kilometers with depths ranging from 700 to 4,500 meters. Fracture zones also host mineralization processes, including the formation of metallic sulfides due to hydrothermal activity along their traces, contributing to Earth's seafloor resource potential. Ubiquitous along the global system, they provide critical insights into the history of plate motions and the evolution of the .

Definition and Characteristics

Geological Definition

A fracture zone is defined as a linear, inactive extension of a on the ocean floor, formed as a from the offset of segments during . These features preserve the inactive portions of ridge-transform systems, where the seafloor on either side moves apart symmetrically away from the ridge axis, leaving behind a topographic discontinuity. Fracture zones were first systematically identified in the mid-20th century through pioneering bathymetric and magnetic surveys of the ocean floor. In 1958, H.W. Menard and V. Vacquier mapped the Murray fracture zone off the coast, revealing its role in displacing magnetic anomalies and providing early evidence of lateral offsets in . Building on this, Harry Hess contributed significantly in the early 1960s by integrating fracture zones into his hypothesis, proposing in his 1962 paper that they represented relict structures from past tectonic activity at spreading centers. In terms of scale, fracture zones typically extend hundreds to thousands of kilometers in length, tracing the history of plate separation over geological time, while remaining relatively narrow at 5-100 kilometers wide. They exhibit notable topographic relief, with elevations or depressions reaching up to 2-3 kilometers relative to the adjacent abyssal plains, reflecting preserved contrasts in crustal age and thickness across the zone.

Morphological Features

Fracture zones exhibit a distinctive linear on the seafloor, characterized by an en echelon arrangement of scarps, , and ridges that extend for hundreds of kilometers. These features often form a prominent central or trough, typically 1,000 to 2,500 meters deep relative to the surrounding seafloor, flanked by elevated transverse ridges and blocks that rise up to 2,000 meters above the valley floor. The scarps are commonly steep, particularly on the south-facing walls in examples like the Kane Fracture Zone, while the ridges display continuity with the fabric of adjacent . Sediments along fracture zones are generally thinner than those on adjacent abyssal plains, where thick deposits can smooth underlying ; this thinner cover, often partial and less than 1 km in places, exposes rugged features more prominently. In some cases, fracture zones are associated with variations in crustal thickness, including locally thickened or chains of seamounts and volcanic structures, as observed in regions with enhanced . Bathymetrically, fracture zones display depths typically ranging from 3 to 5 km, with notable offsets in depth contours that highlight discontinuities in seafloor age and past segmentation. These offsets create step-like variations in the seafloor profile, where the younger side of the zone may appear as a broad rise and the older side as a narrower or low. Fracture zones are primarily identified through high-resolution seafloor mapping techniques, including systems and multibeam echosounders that reveal detailed bathymetric and structural lineations. Additionally, satellite altimetry detects them via associated anomalies, where linear variations in the field align with the zones' traces, enabling global identification even in unsurveyed areas.

Formation and Development

Origin at Mid-Ocean Ridges

zones originate at mid-ocean ridges, where discontinuities or offsets in the spreading ridge axis are accommodated by transform faults that connect adjacent ridge segments, forming ridge-transform-ridge (RTR) systems. These transform faults facilitate strike-slip motion between the offset segments, allowing continuous despite the en echelon arrangement of the ridge. As proposed in early kinematic models, the transform faults maintain orthogonality to the ridge axis due to the rotational nature of plate motions around Euler poles, minimizing and energy dissipation during accretion. During active spreading, the central portion of the transform fault remains tectonically active, but as ridge propagation and jumping occur, the extensions beyond the ridge tips become inactive. These inactive segments "freeze" into fracture zones as the newly formed oceanic lithosphere cools and rigidifies away from the ridge crest, preserving the sheared fabric without ongoing displacement. Analog models using freezing wax have demonstrated this evolution, showing how RTR configurations develop into linear, sheared zones that extend thousands of kilometers perpendicular to the ridge trend. Numerical simulations further support that thermal weakening near the ridge sustains activity, while distal cooling halts it, resulting in fracture zones as relics of past ing. The formation of fracture zones is intrinsically linked to the initiation of , with the oldest preserved examples dating back to the onset of rifting approximately 180 million years ago in the . In the Central Atlantic, magnetic anomalies indicate that initial offsets along the led to the development of major fracture zones like the and Romanche, which trace the early plate boundaries. These zones reflect ridge segment interactions during continental breakup, where preexisting crustal weaknesses influenced nucleation. Diagrams of RTR systems illustrate this progression: active shearing at the ridge intersection transitions to passive, offset scars as spreading continues, highlighting the dynamic interplay of accretion and kinematics.

Post-Formation Evolution

Following their initial formation, oceanic fracture zones experience subsidence driven by the cooling and thickening of the as plates diverge from mid-ocean ridges. This process results in differential , where the older lithospheric segment on one side of the fracture zone cools and deepens more rapidly than the younger segment, preserving a characteristic bathymetric step if the zone remains mechanically strong and locked against slip. In cases of weaker zones with yield strengths below 10 MPa, partial slip allows for some equalization, leading to a gradual decay in topographic relief over the first few million years. Sediments accumulate preferentially in topographic lows along these features, further smoothing their expression as the lithosphere ages. The evolution of fracture zone depths adheres to patterns predicted by half-space cooling models of oceanic . Specifically, ocean floor depth increases approximately as d≈2.5 km+350td \approx 2.5 \, \text{km} + 350 \sqrt{t}
Add your contribution
Related Hubs
User Avatar
No comments yet.