Ninety East Ridge
Encyclopedia
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
chain in the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and is named for its near-parallel strike along the 90th meridian
90th meridian east
The meridian 90° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole.The Ninety East Ridge is named after the meridian....
. It is approximately 5000 kilometres (3,106.9 mi) in length and can be traced topographically from the Bay of Bengal
Bay of Bengal
The Bay of Bengal , the largest bay in the world, forms the northeastern part of the Indian Ocean. It resembles a triangle in shape, and is bordered mostly by the Eastern Coast of India, southern coast of Bangladesh and Sri Lanka to the west and Burma and the Andaman and Nicobar Islands to the...
southward towards the Southeast Indian Ridge
Southeast Indian Ridge
The Southeast Indian Ridge is a divergent tectonic plate boundary located along the seafloor of the southern Indian Ocean. It separates the Indo-Australian Plate to the north from the Antarctic Plate to the south...
(SEIR), though the feature continues to the north where it is hidden beneath the sediments of the Bengal Fan. The ridge extends between latitudes 33°S
33rd parallel south
The 33rd parallel south is a circle of latitude that is 33 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, Africa, the Indian Ocean, Australasia, the Pacific Ocean and South America....
and 17°N
17th parallel north
The 17th parallel north is a circle of latitude that is 17 degrees north of the Earth's equatorial plane. It crosses Africa, Asia, the Indian Ocean, the Pacific Ocean, Central America, the Caribbean and the Atlantic Ocean....
and has an average width of 200 km.
The ridge dissects the Indian Ocean into the West and East Indian Ocean. The northeastern side is named the Wharton Basin
Wharton Basin
Wharton BasinIs the named part of the marine area of the north east quarter of the Indian Ocean.It lies east of the Ninety East Ridge and west of Western Australia....
and ceases at the western end of the Diamantina Fracture Zone which passes to the east and almost to the Australian continent.
The ridge is primarily composed of Ocean Island Tholeiites (OIT), a subset of basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
which increase in age from approximately 43.2 ± 0.5 Ma in the south to 81.8 ± 2.6 Ma in the north though a more recent analysis using modern Ar-Ar techniques is currently pending publication. This age progression has led geologists to theorize that a hotspot
Hotspot (geology)
The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...
in the mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
beneath the Indo-Australian Plate
Indo-Australian Plate
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...
created the ridge as the plate has moved northward in the late Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
and Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
. This theory is supported by a detailed analysis of the chemistry of the Kerguelen Plateau
Kerguelen Plateau
The Kerguelen Plateau is an underwater volcanic large igneous province , also the microcontinent and submerged continent in the southern Indian Ocean. It lies about 3,000 km to the southwest of Australia and is nearly three times the size of Japan...
and Rajmahal Traps, which together, geologists believe, represent the flood basalt
Flood basalt
A flood basalt or trap basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava. Flood basalts have occurred on continental scales in prehistory, creating great plateaus and mountain ranges...
s erupted at the initiation of volcanism at the Kerguelen hotspot
Kerguelen hotspot
The Kerguelen hotspot is a volcanic hotspot at the Kerguelen Plateau in the Southern Indian Ocean. The Kerguelen hotspot has produced basaltic lava for about 130 million years and has also produced the Kerguelen Islands, Heard Island, the McDonald Islands, and the Ninetyeast Ridge....
which was then sheared in two as the Indian subcontinent moved northward. However, the existence of so-called deep mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
hotspots
Hotspot (geology)
The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...
is currently a topic of debate in the geologic community, with many geochemists favoring an alternative hypothesis which postulates a much shallower origin for hotspot
Hotspot (geology)
The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...
volcanism.
The ridge has been surveyed several times in the past, including several times by the Deep Sea Drilling Program
Deep Sea Drilling Program
The Deep Sea Drilling Project was an ocean drilling project operated from 1968 to 1983. The program was considered to be successful as evidenced by the data and publications that have resulted from it and is now supported by Texas A&M University, although for the years of its operations these were...
(DSDP). In 2007, the RV Roger Revelle collected bathymetric, magnetic and seismic data together with dredge samples from nine sites along the ridge as part of an Integrated Ocean Drilling Program
Integrated Ocean Drilling Program
The Integrated Ocean Drilling Program is an international marine research program. The program uses heavy drilling equipment mounted aboard ships to monitor and sample sub-seafloor environments...
(IODP) site survey intended to examine the hotspot hypothesis for the ridge.