The Owen Fracture Zone (OFZ), though misnamed 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 e ...

, is a

transform fault A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subduct ...

in the northwest

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by ...

that separates the

Arabian The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plat ...

and

African Plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plate ...

s from the

Indian Plate The Indian Plate (or India Plate) is a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian Plate broke away from the other fragments of Gondwana , began ...

. Extending north-northeast from where the

Carlsberg Ridge The Carlsberg Ridge is the northern section of the Central Indian Ridge, a divergent tectonic plate boundary between the African Plate and the Indo-Australian Plate, traversing the western regions of the Indian Ocean. The ridge of which the Carl ...

meets the

Sheba ridge The Aden Ridge is a part of an active oblique rift system located in the Gulf of Aden, between Somalia and the Arabian Peninsula to the north. The rift system marks the divergent boundary between the Somali and Arabian tectonic plates, extending ...

in the south to the

Makran Subduction Zone Makran ( fa, مكران), mentioned in some sources as Mecran and Mokrān, is the coastal region of Baluchistan. It is a semi-desert coastal strip in Balochistan, in Pakistan and Iran, along the coast of the Gulf of Oman. It extends westwards, f ...

in the north, it represents the port side of the northward motion of the

Indian subcontinent The Indian subcontinent is a physiographical region in Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian Ocean from the Himalayas. Geopolitically, it includes the countries of Bangladesh, Bhutan, In ...

during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

–

Palaeogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( Mya) to the beginning ...

break-up of

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...

. Slip along the Owen Fracture Zone is occurring at /yr, the slowest rate on Earth, which means the Arabian Plate moves northward faster than the Indian Plate (4 vs. 2 mm/yr). In some usages, the name Owen Transform Fault is used to denote the short section between the end of the Aden-Sheba ridge and the Carlsberg Ridge. Additionally, this area has been called the

Aden-Owen-Carlsberg Triple Junction The Aden-Owen-Carlsberg Triple Junction (AOC), also known as the Arabia–India–Somalia Triple Junction, is a triple junction that connects the Aden Ridge, Owen Fracture Zone, and Carlsberg Ridge in the northwest Indian Ocean. It has been des ...

, although the Carlsberg Ridge is offset from the point where the Owen Fracture Zone/Fault intersects the Sheba segment of the Aden Ridge. Owen Fracture Zone is named after HMS ''Owen'' that identified the 'fracture line' in April/May 1963. The Owen fracture Zone and the Dalrymple Trough north of it (named after HMS ''Dalrymple'' surveyed the area together with HMS ''Owen'') form the modern boundary between the Arabian and Indian Plates.

Bathymetry and oceanography

-long, the Owen Fracture Zone runs along the Owen Ridge which is divided into two. The Southern Owen Ridge, and -wide, is a near-linear structure that drops steeply on its eastern side. The top layers of the Southern Ridge are formed by the Oligocene-Early Miocene

turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites wer ...

s of the Indus River Fan and later cover. The Central Owen ridge, -long and -wide, in contrast, is more uneven and reaches a maximum height of . The Qalhat Seamount and Murray Ridge are located at the northern end of the Owen Fracture Zone. The exchange of deep water from the

Somali Basin Somali may refer to: Horn of Africa * Somalis, an inhabitant or ethnicity associated with Greater Somali Region ** Proto-Somali, the ancestors of modern Somalis ** Somali culture ** Somali cuisine ** Somali language, a Cushitic language ** Somali, ...

to the

Arabian Basin The Arabian Basin is an oceanic basin located in the southern part of the Arabian Sea between the Arabian Peninsula and India. It is centered at 10° N, 65° E. The basin depth ranges from 3,400 m in the north to 4,400 m in the ...

through the OFZ has been estimated to 2 Sv. In the Arabian Basin the current splits into a northern and southern branch that both flow parallel to the Carlsberg Ridge.

Plate tectonics

Seafloor spreading in the Sheba ridge began . Subduction in the Makran Trench was initiated in the Late Cretaceous and the

accretionary wedge An accretionary wedge or accretionary prism forms from sediments accreted onto the non- subducting tectonic plate at a convergent plate boundary. Most of the material in the accretionary wedge consists of marine sediments scraped off from the d ...

there developed . Seismic lines from drillings in the 1970s and 1980s beneath both ridges revealed a structure now known as the -old Proto-Owen Ridge which was uplifted and rejuvenated during the Early Miocene. According to one reconstruction, before the initiation of the Carlsberg Ridge the Arabian–Indian boundary was located off Oman while the Mascarene Basin opened between Madagascar and the Seychelles. In the Early Miocene ( ) the boundary jumped to its present location which uplifted the Owen Ridge. -long offsets along the OFZ indicate a 3-6 Ma-old dextral strike-slip motion but this motion can be extended to 20 Ma based on magnetic anomaly reconstructions. This coincides with a general reorganisation of continental plates in the Indian Ocean in response to the Arabia-Eurasia collision.

References

Notes

Sources

* * * * * * * * * {{Refend Fracture zones Geology of the Indian Ocean Plate tectonics