The Broken Ridge or Broken Plateau is an

oceanic plateau An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. There are 184 oceanic plateaus in the world, covering an area of or about 5.11% of the ...

in the south-eastern

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 ...

. The Broken Ridge once formed a

large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation ...

(LIP) together with the

Kerguelen Plateau The Kerguelen Plateau (, ), also known as the Kerguelen–Heard Plateau, is an oceanic plateau and a large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean. It is about to the southwest of Australia and is ...

. When Australia and Antarctica started to separate, the Broken Ridge and the Kerguelen Plateau got separated by the

Southeast Indian Ridge The Southeast Indian Ridge (SEIR) is a mid-ocean ridge in the southern Indian Ocean. A divergent tectonic plate boundary stretching almost between the Rodrigues Triple Junction () in the Indian Ocean and the Macquarie Triple Junction () in t ...

. Alkalic

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

from the Broken Ridge has been dated to 95 Ma. The Broken Ridge stretches from the southern end of the

Ninety East Ridge The Ninety East Ridge (also rendered as Ninetyeast Ridge, 90E Ridge or 90°E Ridge) is a mid-ocean ridge on the Indian Ocean floor named for its near-parallel strike along the 90th meridian at the center of the Eastern Hemisphere. It is approxima ...

towards the south-western corner of

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

. It is up to wide and reaches below sea level. It is separated from the

Diamantina Fracture Zone The Diamantina Fracture Zone (DFZ) is an area of the south-eastern Indian Ocean seafloor, consisting of a range of ridges and trenches. It lies to the south of the mideastern Indian Ocean features of the Wharton Basin and Perth Basin, an ...

on its southern side by a escarpment, while on the northern side the ridge slopes gently towards the abyssal

Wharton Basin Wharton Basin is the marine area of the north east quarter of the Indian Ocean. It is named after William Wharton (1843-1905), Hydrographer of the Navy. Alternative names are Cocos Basin (after the Cocos Islands) and West Australian Basin. It ...

. The sediment cover on the ridge reaches and the Moho is found at about . It is separated from the Naturaliste Plateau by the Dirck Hartog Ridge. The Kerguelen LIP covered making it the second largest LIP on Earth (after the

Ontong Java Plateau The Ontong Java Plateau (OJP) is a massive oceanic plateau located in the southwestern Pacific Ocean, north of the Solomon Islands. The OJP was formed around (Ma) with a much smaller volcanic event around 90 Ma. Two other southwestern Pacifi ...

in the Pacific). Both these enormous LIPs reaches above the surrounding ocean floor and have a crustal thickness of (compared to oceanic crust typically around thick.) The Broken Ridge and Kerguelen Plateau are now separated by . When they broke-up, the southern flank of Broken Ridge was uplifted some and reached above sea level. The Kerguelen LIP has a long and complicated history, however, and is probably the least "typical" of all LIPs. Rocks from both the Broken Ridge and the Kerguelen Plateau contain a continental component or "fingerprint". In the Early Cretaceous, the

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, Naturaliste Plateau, Hea ...

was split into several

diapir A diapir (; , ) is a type of igneous intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–T ...

s of various sizes, composition, and ascent rates. These separate diapirs created the Bunbury Basalt, the Southern Kerguelen Plateau, the

Rajmahal Traps The Rajmahal Traps is a volcanic igneous province in Eastern India, covering the parts of Jharkhand, West Bengal and Meghalaya. The Rajmahal Hills of Jharkhand is the type area of this province. Multiple layers of solidified lava made the Rajma ...

/Indian

lamprophyre Lamprophyres () are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica- undersaturated mafic or ultramafic rocks with high magnesium ...

s, Antarctic lamprophyres, and the Central Kerguelen Plateau/Broken Ridge. In the late Cretaceous, activity in the mantle slowed and the Kerguelen hotspot was reduced to a single plume which created the Ninety East Ridge. 120-95 Ma when the Southern and Central Kerguelen Plateau formed together with the Broken Ridge, the Kerguelen hotspot produced /year, but 95-25 Ma the output decreased to .

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* * * * {{Large igneous provinces Large igneous provinces Plateaus of the Indian Ocean Cretaceous volcanism