31°S 95°E / 31°S 95°E / -31; 95
20-708: The Broken Ridge or Broken Plateau is an oceanic plateau in the south-eastern Indian Ocean . The Broken Ridge once formed a large igneous province (LIP) together with the Kerguelen Plateau . When Australia and Antarctica started to separate, the Broken Ridge and the Kerguelen Plateau got separated by the Southeast Indian Ridge . Alkalic basalt from the Broken Ridge has been dated to 95 Ma. The Broken Ridge stretches 1,200 km (750 mi) from
40-532: A better record of large-scale volcanic eruptions throughout Earth's history. This "docking" also means that oceanic plateaus are important contributors to the growth of continental crust. Their formations often had a dramatic impact on global climate, such as the most recent plateaus formed, the three, large, Cretaceous oceanic plateaus in the Pacific and Indian Ocean: Ontong Java, Kerguelen, and Caribbean. Geologists believe that igneous oceanic plateaus may well represent
60-651: 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 was split into several diapirs of various sizes, composition, and ascent rates. These separate diapirs created the Bunbury Basalt , the Southern Kerguelen Plateau,
80-415: A ratio intermediate between continental and oceanic crust, although they are more mafic than felsic. However, when a plate carrying oceanic crust subducts under a plate carrying an igneous oceanic plateau, the volcanism which erupts on the plateau as the oceanic crust heats up on its descent into the mantle erupts material which is more felsic than the material which makes up the plateau. This represents
100-456: A stage in the development of continental crust as they are generally less dense than oceanic crust while still being denser than normal continental crust. Density differences in crustal material largely arise from different ratios of various elements, especially silicon . Continental crust has the highest amount of silicon (such rock is called felsic ). Oceanic crust has a smaller amount of silicon ( mafic rock). Igneous oceanic plateaus have
120-447: A step toward creating crust which is increasingly continental in character, being less dense and more buoyant. If an igneous oceanic plateau is subducted underneath another one, or under existing continental crust, the eruptions produced thereby produce material that is yet more felsic, and so on through geologic time. Lord Howe Rise The Lord Howe Rise is a deep sea plateau which extends from south west of New Caledonia to
140-597: Is composed of continental crust . Some have included the 3,500 m (11,500 ft) deep New Caledonia Basin as within the rise, given its continental crust origin, and this would give a larger total area of 1,950,000 km (750,000 sq mi). The Lord Howe Rise is associated with seafloor spreading which also resulted in the creation of the Tasman Sea. The geology has not yet been characterised as well as other parts of Zealandia but when previous samples are analysed with current geological techniques they fit with
160-639: The Challenger Plateau , west of New Zealand in the south west of the Pacific Ocean . To its west is the Tasman Basin and to the east is the New Caledonia Basin . Lord Howe Rise has a total area of about 1,500,000 km (580,000 sq mi), and generally lies about 750 to 1,200 metres under water. It is part of Zealandia , a much larger continent that is now mostly submerged, and so
180-888: The Falkland Plateau , Lord Howe Rise , and parts of Kerguelen , Seychelles , and Arctic ridges. Plateaus formed by large igneous provinces were formed by the equivalent of continental flood basalts such as the Deccan Traps in India and the Snake River Plain in the United States. In contrast to continental flood basalts, most igneous oceanic plateaus erupt through young and thin (6–7 km (3.7–4.3 mi)) mafic or ultra-mafic crust and are therefore uncontaminated by felsic crust and representative for their mantle sources. These plateaus often rise 2–3 km (1.2–1.9 mi) above
200-617: The Miocene period when this part of Zealandia existed over the Lord Howe hotspot . One rhyolite sample has been dated at 97 million years drilled on the southern Lord Howe Rise. Lord Howe Island was the last volcano to erupt on the rise 6.5 million years ago. Lord Howe Island and Ball's Pyramid cap a seamount towards the central east of the rise in an area known as the Lord Howe platform. The Lord Howe Seamount Chain extends northwards along
220-743: The Rajmahal Traps /Indian lamprophyres , 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 1 km (0.24 cu mi)/year, but 95–25 Ma
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#1732855936197240-516: The Zealandia hypothesis. The seafloor is known to be dominated by soft sediments and the highest quality recent survey only mapped approximately 25,500 km (9,800 sq mi) of the western flank of the rise which is less than 1% of the total area of the rise. In this area about 0.1% of the rises seafloor was classed as hard substrata based on a combined area of 31 km (12 sq mi) for 16 volcanic peaks. Sandstone rocks dredged from
260-480: The central Lord Howe Rise contained granite pebbles that were in the range 216–183 million years old. It was rifted away from Eastern Australia in association with a mid-ocean ridge that was active from 80 to 60 million years ago, and now lies 800 kilometres offshore from mainland Australia . The Lord Howe Rise contains a line of seamounts called the Lord Howe Seamount Chain which formed during
280-576: The oceans. The South Pacific region around Australia and New Zealand contains the greatest number of oceanic plateaus (see map). Oceanic plateaus produced by large igneous provinces are often associated with hotspots , mantle plumes , and volcanic islands — such as Iceland, Hawaii, Cape Verde, and Kerguelen. The three largest plateaus, the Caribbean , Ontong Java , and Mid-Pacific Mountains , are located on thermal swells . Other oceanic plateaus, however, are made of rifted continental crust, for example
300-480: The output decreased to 0.1 km (0.024 cu mi). Oceanic plateau 3°03′S 160°23′E / 3.050°S 160.383°E / -3.050; 160.383 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 18,486,600 km (7,137,700 sq mi) or about 5.11% of
320-705: The ridge reaches 800 m (2,600 ft) and the Moho is found at about 20 km (12 mi). It is separated from the Naturaliste Plateau by the Dirck Hartog Ridge . The Kerguelen LIP covered 2.3 × 10 ^ km (0.89 × 10 ^ sq mi) making it the second largest LIP on Earth (after the Ontong Java Plateau in the Pacific). Both these enormous LIPs reaches 2–4 km (1.2–2.5 mi) above
340-510: The rise. The seamounts provide habitat to a diverse range of marine species which attracts commercial fishers, but cover a very small area, less than 1% of the total area of Lord Howe Rise. Further north is the Elizabeth and Middleton part of the Coral Sea Islands , which together with reefs around Lord Howe Island are the most southern coral reefs on Earth. The seabed on the rise
360-548: The southern end of the Ninety East Ridge towards the south-western corner of Australia . It is up to 400 km (250 mi) wide and reaches 1,000 m (3,300 ft) below sea level. It is separated from the Diamantina Fracture Zone on its southern side by a 3,000 m (9,800 ft) escarpment, while on the northern side the ridge slopes gently towards the abyssal Wharton Basin . The sediment cover on
380-414: The surrounding ocean floor and are more buoyant than oceanic crust. They therefore tend to withstand subduction, more-so when thick and when reaching subduction zones shortly after their formations. As a consequence, they tend to "dock" to continental margins and be preserved as accreted terranes . Such terranes are often better preserved than the exposed parts of continental flood basalts and are therefore
400-412: The surrounding ocean floor and have a crustal thickness of 20–40 km (12–25 mi) (compared to oceanic crust typically around 7 km (4.3 mi) thick.) The Broken Ridge and Kerguelen Plateau are now separated by 1,800 km (1,100 mi). When they broke-up, the southern flank of Broken Ridge was uplifted some 2,000 m (6,600 ft) and reached above sea level. The Kerguelen LIP has
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