![Owen](https://upload.wikimedia.org/wikipedia/commons/3/3d/Owen.svg)
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 eit ...
, 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 subductio ...
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 th ...
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 Plate. ...
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 mov ...
. Extending north-northeast from where the
Carlsberg Ridge 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 in the north, it represents the port side of the northward motion of the
Indian subcontinent
The Indian subcontinent is a list of the physiographic regions of the world, physiographical region in United Nations geoscheme for Asia#Southern Asia, Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian O ...
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'', the ...
–
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 o ...
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 stages ...
. 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 d ...
, 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 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 do ...
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
In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...
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