Lansdowne Bank , sometimes called Landsdowne Bank , is an extensive submerged bank located between the main island of New Caledonia and the Chesterfield Islands , in the easternmost part of the Coral Sea . It covers an area of 4,300 km (1,660 sq mi), making it one of the largest banks of the world, has general depths of 60 to 80 metres (197–262 ft), and a largely sandy bottom. Two reefs mark the shallowest spots of the bank, but they are still submerged at low tide.
29-565: Fairway Ridge , also called Fairway Plateau , is a submarine feature shown on some maps in that area. The Lansdowne Bank area marked is far larger than Fairway Plateau, but there are smaller, unnamed plateaus nearby. The Lansdowne Bank area, shown at the northeastern end of Lord Howe Rise , is separated from New Caledonia by the northern New Caledonia Trough . Nereus Reef is at the northern end of Lansdowne Bank. Its given position of 20°07′S 160°28′E / 20.117°S 160.467°E / -20.117; 160.467 ( Nereus Reef )
58-449: A lacustrine environment or in a restricted marine environment, although not all rifts contain such sequences. Reservoir rocks may be developed in pre-rift, syn-rift and post-rift sequences. Effective regional seals may be present within the post-rift sequence if mudstones or evaporites are deposited. Just over half of estimated oil reserves are found associated with rifts containing marine syn-rift and post-rift sequences, just under
87-431: A central linear downfaulted depression, called a graben , or more commonly a half-graben with normal faulting and rift-flank uplifts mainly on one side. Where rifts remain above sea level they form a rift valley , which may be filled by water forming a rift lake . The axis of the rift area may contain volcanic rocks , and active volcanism is a part of many, but not all, active rift systems. Major rifts occur along
116-462: A high angle. These segment boundary zones accommodate the differences in fault displacement between the segments and are therefore known as accommodation zones. Accommodation zones take various forms, from a simple relay ramp at the overlap between two major faults of the same polarity, to zones of high structural complexity, particularly where the segments have opposite polarity. Accommodation zones may be located where older crustal structures intersect
145-403: A kind of orogeneses in extensional settings, which is referred as to rifting orogeny. Once rifting ceases, the mantle beneath the rift cools and this is accompanied by a broad area of post-rift subsidence. The amount of subsidence is directly related to the amount of thinning during the rifting phase calculated as the beta factor (initial crustal thickness divided by final crustal thickness), but
174-438: A mid-oceanic ridge and a set of conjugate margins separated by an oceanic basin. Rifting may be active, and controlled by mantle convection . It may also be passive, and driven by far-field tectonic forces that stretch the lithosphere. Margin architecture develops due to spatial and temporal relationships between extensional deformation phases. Margin segmentation eventually leads to the formation of rift domains with variations of
203-553: Is 3.2 kilometres (2.0 mi) long, about 4 to 5 fathoms (7.3 to 9.1 metres) deep, of coral bottom, and located at 21°00′15″S 161°45′09″E / 21.00417°S 161.75250°E / -21.00417; 161.75250 ( Fairway Reef ) . According to some sources, Fairway Reef dries at low tide. Google Maps and other internet maps showed a large landmass named Sandy Island in northern Lansdowne Bank, but did not show an image for it. The non-existence of this phantom island had been proved by French missions in
232-402: Is also affected by the degree to which the rift basin is filled at each stage, due to the greater density of sediments in contrast to water. The simple 'McKenzie model' of rifting, which considers the rifting stage to be instantaneous, provides a good first order estimate of the amount of crustal thinning from observations of the amount of post-rift subsidence. This has generally been replaced by
261-597: 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
290-563: Is doubtful. Nereus Reef has the least depth of the bank, with 3.7 metres (12 ft). A shoal with a depth of 16 metres (52 ft) is 14 miles (23 km) west-northwest of Nereus Reef. The southeastern end of Lansdowne Bank is marked by Fairway Reef, thus named from its lying in the fairway between Australia and New Caledonia , midway between the Bellona Reefs (south of the Chesterfield Islands) and New Caledonia. Fairway Reef
319-559: Is mostly sandy mud with some volcanic outcrops, gravel and boulders. The doubleheader fish, Coris bulbifrons , is endemic to reefs on the Lord Howe Rise and the West Norfolk Rise . Much of the basin remains unexplored in relation to oil and gas reserves. Rift In geology , a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics . Typical rift features are
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#1732852422437348-811: Is thinned, the Earth's surface subsides and the Moho becomes correspondingly raised. At the same time, the mantle lithosphere becomes thinned, causing a rise of the top of the asthenosphere. This brings high heat flow from the upwelling asthenosphere into the thinning lithosphere, heating the orogenic lithosphere for dehydration melting, typically causing extreme metamorphism at high thermal gradients of greater than 30 °C. The metamorphic products are high to ultrahigh temperature granulites and their associated migmatite and granites in collisional orogens, with possible emplacement of metamorphic core complexes in continental rift zones but oceanic core complexes in spreading ridges. This leads to
377-639: 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
406-617: 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
435-423: The Moho topography, including proximal domain with fault-rotated crustal blocks, necking zone with thinning of crustal basement , distal domain with deep sag basins, ocean-continent transition and oceanic domain. Deformation and magmatism interact during rift evolution. Magma-rich and magma-poor rifted margins may be formed. Magma-rich margins include major volcanic features. Globally, volcanic margins represent
464-645: The 'flexural cantilever model', which takes into account the geometry of the rift faults and the flexural isostasy of the upper part of the crust. Some rifts show a complex and prolonged history of rifting, with several distinct phases. The North Sea rift shows evidence of several separate rift phases from the Permian through to the Earliest Cretaceous , a period of over 100 million years. Rifting may lead to continental breakup and formation of oceanic basins. Successful rifting leads to seafloor spreading along
493-515: The 1970s, and the information passed to hydrographic services around the world, but it had remained in the World Vector Shoreline Database. In 2012 Australian scientists again proved the island does not exist. 20°35′S 160°30′E / 20.583°S 160.500°E / -20.583; 160.500 Lord Howe Rise The Lord Howe Rise is a deep sea plateau which extends from south west of New Caledonia to
522-454: The Baikal Rift have segment lengths in excess of 80 km, while in areas of warmer thin lithosphere, segment lengths may be less than 30 km. Along the axis of the rift the position, and in some cases the polarity (the dip direction), of the main rift bounding fault changes from segment to segment. Segment boundaries often have a more complex structure and generally cross the rift axis at
551-516: 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
580-480: 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
609-422: The central axis of most mid-ocean ridges , where new oceanic crust and lithosphere is created along a divergent boundary between two tectonic plates . Failed rifts are the result of continental rifting that failed to continue to the point of break-up. Typically the transition from rifting to spreading develops at a triple junction where three converging rifts meet over a hotspot . Two of these evolve to
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#1732852422437638-402: The larger bounding faults. Subsequent extension becomes concentrated on these faults. The longer faults and wider fault spacing leads to more continuous areas of fault-related subsidence along the rift axis. Significant uplift of the rift shoulders develops at this stage, strongly influencing drainage and sedimentation in the rift basins. During the climax of lithospheric rifting, as the crust
667-567: The majority of passive continental margins. Magma-starved rifted margins are affected by large-scale faulting and crustal hyperextension. As a consequence, upper mantle peridotites and gabbros are commonly exposed and serpentinized along extensional detachments at the seafloor. Many rifts are the sites of at least minor magmatic activity , particularly in the early stages of rifting. Alkali basalts and bimodal volcanism are common products of rift-related magmatism. Recent studies indicate that post-collisional granites in collisional orogens are
696-411: The onset of rifting, the upper part of the lithosphere starts to extend on a series of initially unconnected normal faults , leading to the development of isolated basins. In subaerial rifts, for example, drainage at the onset of rifting is generally internal, with no element of through drainage. As the rift evolves, some of the individual fault segments grow, eventually becoming linked together to form
725-456: The point of seafloor spreading, while the third ultimately fails, becoming an aulacogen . Most rifts consist of a series of separate segments that together form the linear zone characteristic of rifts. The individual rift segments have a dominantly half-graben geometry, controlled by a single basin-bounding fault. Segment lengths vary between rifts, depending on the elastic thickness of the lithosphere. Areas of thick colder lithosphere, such as
754-404: The product of rifting magmatism at converged plate margins. The sedimentary rocks associated with continental rifts host important deposits of both minerals and hydrocarbons . SedEx mineral deposits are found mainly in continental rift settings. They form within post-rift sequences when hydrothermal fluids associated with magmatic activity are expelled at the seabed. Continental rifts are
783-838: The rift axis. In the Gulf of Suez rift, the Zaafarana accommodation zone is located where a shear zone in the Arabian-Nubian Shield meets the rift. Rift flanks or shoulders are elevated areas around rifts. Rift shoulders are typically about 70 km wide. Contrary to what was previously thought, elevated passive continental margins (EPCM) such as the Brazilian Highlands , the Scandinavian Mountains and India's Western Ghats , are not rift shoulders. The formation of rift basins and strain localization reflects rift maturity. At
812-510: 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
841-510: The sites of significant oil and gas accumulations, such as the Viking Graben and the Gulf of Suez Rift . Thirty percent of giant oil and gas fields are found within such a setting. In 1999 it was estimated that there were 200 billion barrels of recoverable oil reserves hosted in rifts. Source rocks are often developed within the sediments filling the active rift ( syn-rift ), forming either in
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