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55-591: Exploration of this oceanic region has taken place via sonar, gravity field, magnetic field, a few drill holes and deliberate or accidental dredging of rocks up to the surface. The rise forms a northern extension from the Macquarie-Balleny Ridge which extends to the subantarctic Balleny Islands . To east of the rise is the Tasman Basin , while the South Australian Basin extends westwards, south of

110-513: A zigzag pattern. This results from oblique seafloor spreading where the direction of motion is not perpendicular to the trend of the overall divergent boundary. A smaller number of such faults are found on land, although these are generally better-known, such as the San Andreas Fault and North Anatolian Fault . Transform boundaries are also known as conservative plate boundaries because they involve no addition or loss of lithosphere at

165-512: A component of convergence which increases as it approaches the South Island of New Zealand where it merges into the Alpine Fault which cuts across the continental crust of New Zealand's South Island. The northern and southern ends of the zone are believed to be converging at between 2 and 4 cm (1.6 in)/year presently. It has been observed that the south western portion of the zone has

220-495: A degree the apparent clash with evidence that the Puysegur subduction initiated at 20 million years ago is less challenging to explain. Compositional analysis on this single sample does not exclude the possibility of later oceanic island type origin even if it seems to fit with other samples from the zone. Seafloor spreading must have ceased by 10 million years ago on the central Macquarie segment containing Macquarie Island. Since then

275-409: A junction with another plate boundary, while transcurrent faults may die out without a junction with another fault. Finally, transform faults form a tectonic plate boundary, while transcurrent faults do not. Faults in general are focused areas of deformation or strain , which are the response of built-up stresses in the form of compression , tension, or shear stress in rock at the surface or deep in

330-561: A magnitude of at least M w 8.0 On 23 December 2004 a M w 8.1 event occurred about 150 km (93 mi) to the west of the plate boundary. This event to the west of the plate boundary was close to the transition from oblique subduction at the Puysegur Trough to strike slip, with some compression, on the Macquarie Ridge. It is believed these large events are because the transition to oblique convergence with subduction

385-568: A major central part of the plate convergent structures south of New Zealand that has become to be termed the Macquarie Ridge Complex as the geology has been better characterised. The northern part of this complex is an extension of New Zealand 's Alpine Fault which becomes the Puysegur Trench and ridge to its east. New Zealand is continental crust and the northern parts of the complex are associated with oceanic crust subducting under

440-418: A transform fault links a spreading center and the upper block of a subduction zone or where two upper blocks of subduction zones are linked, the transform fault itself will grow in length. [REDACTED] [REDACTED] Constant length: In other cases, transform faults will remain at a constant length. This steadiness can be attributed to many different causes. In the case of ridge-to-ridge transforms,

495-460: 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 subduction zone . A transform fault is a special case of a strike-slip fault that also forms a plate boundary. Most such faults are found in oceanic crust , where they accommodate the lateral offset between segments of divergent boundaries , forming

550-507: Is being created to change that length. [REDACTED] [REDACTED] Decreasing length faults: In rare cases, transform faults can shrink in length. These occur when two descending subduction plates are linked by a transform fault. In time as the plates are subducted, the transform fault will decrease in length until the transform fault disappears completely, leaving only two subduction zones facing in opposite directions. [REDACTED] [REDACTED] The most prominent examples of

605-435: Is constantly created through the upwelling of new basaltic magma . With new seafloor being pushed and pulled out, the older seafloor slowly slides away from the mid-oceanic ridges toward the continents. Although separated only by tens of kilometers, this separation between segments of the ridges causes portions of the seafloor to push past each other in opposing directions. This lateral movement of seafloors past each other

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660-634: Is located about 4.5 km (2.8 mi) east of the Australian Pacific plate boundary the transform of this to the north of the island is a 15 km (9.3 mi) wide zone of closely spaced NNE- to NE-trending faults while to the south of the island north of the island the zone narrows to as little as 8 km (5.0 mi) with NNE to NNW-trending faults. The fault zone is up to 40 km (25 mi) wide, elsewhere and it often has parallel eastern and western ridge crests, as well as multiple nearby fracture zones. The zone has in historic times been

715-512: Is not particularly seismologically active presently. So while further studies take place the term Australian plate will be used to simplify the tectonics as of the present and this view is not inconsistent with the latest reference frames used in recent plate modelling. The oceanic crust of the Macquarie Fault Zone as found at Macquarie Island was generated however at the divergent Australian-Pacific plate boundary following break-up between

770-546: Is postulated that because the lithosphere would cool and strengthen usually with mid oceanic ridge formation, that if such tectonic inversion is not rapid, it does not lead to the relative simplicity seen at say the Kermadec-Tonga subduction zone . This is not the case with the Macquarie ridge. The localised to segments transpression and compression seen in the Macquarie Ridge Complex took about 10 to 15 million years. The process

825-693: Is putting the area of what has been called the Macquarie Block under significant strain that is eventually relieved by major failure reactivating past transform faults in the oceanic crust of the Tasman sea floor. The basalts which are oceanic in the zone have been dated. To the south east of the Puysegur Trench a seamount is as young as 1.59 ± 0.26 million years. It is not yet known for sure if this relatively recent date could be related to late mid ocean ridge spreading or back arc activity. The recent dating of

880-601: Is related to the Macquarie triple junction which was created about 47.91 million years ago. The Macquarie Ridge is a very long, but incompletely studied extinct mid-ocean ridge system which has since experienced complex tectonic processes over about 30 million years that have differed down its length as it became the Australian–Pacific plate boundary. Not all timings derived from different methodologies concord as well as they do for easier to study tectonic structures. It

935-442: Is summarised as: This last stage has been difficult to characterise as the usual approach through magnetic anomaly studies only allowed a good time for the central McDougall and Macquarie segments spreading ceasing by 24 million years ago and either end was only constrained to the 30 million years ago estimate. It is now known to have occurred differentially, with cessation of sea floor spreading happening at 25.9 million years ago in

990-869: Is the San Andreas Fault on the Pacific coast of the United States. The San Andreas Fault links the East Pacific Rise off the West coast of Mexico (Gulf of California) to the Mendocino Triple Junction (Part of the Juan de Fuca plate ) off the coast of the Northwestern United States , making it a ridge-to-transform-style fault. The formation of the San Andreas Fault system occurred fairly recently during

1045-435: Is where transform faults are currently active. Transform faults move differently from a strike-slip fault at the mid-oceanic ridge. Instead of the ridges moving away from each other, as they do in other strike-slip faults, transform-fault ridges remain in the same, fixed locations, and the new ocean seafloor created at the ridges is pushed away from the ridge. Evidence of this motion can be found in paleomagnetic striping on

1100-500: The Campbell Plateau and Resolution Ridge between the middle Eocene about 40 million years ago and what was formally thought to be the late Miocene. However this cessation of seafloor spreading generally propagated from south at 25.9 million years ago to north along the ridge where it is now known that it might have stopped as recently as 1.6 million years ago although an earlier date remains possible. Many researchers conclude that

1155-469: The Great Australian Bight . The rise contains a number of seamounts , some of which have flat summits, indicating exposure above the sea surface at some time. The rise most probably originates from subsided continental crust that fragmented as Australia and Antarctica separated. This area of the seafloor is slated for exploration of offshore oil reserves. No oil has been recovered from

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1210-633: The Macquarie Ridge , its gazetted name since 2015, the Macquarie Ridge Complex or historically as the Macquarie Fault ) is a major right lateral-moving transform fault along the seafloor of the south Pacific Ocean which runs from New Zealand southwestward towards the Macquarie triple junction . It is also the tectonic plate boundary between the Australian plate to the northwest and

1265-673: The Oligocene Period between 34 million and 24 million years ago. During this period, the Farallon plate , followed by the Pacific plate, collided into the North American plate . The collision led to the subduction of the Farallon plate underneath the North American plate. Once the spreading center separating the Pacific and the Farallon plates was subducted beneath the North American plate,

1320-632: The Orange Roughy and Oreo Dory using deepwater demersal trawlers. The northern part of the South Tasman Rise lies in the Australian Fishing Zone, in the exclusive economic zone of Australia, but the south end lies in international waters. Orange Roughy ( Hoplostethus atlanticus ) is an important fish found between 1 and 2 km deep on the South Tasman Rise. Fishing for orange roughy in international waters ramped up in late 1997. 1998 saw

1375-515: The Pacific plate to the southeast. As such it is a region of high seismic activity and recorded the largest strike-slip event on record up to 23 May 1989, of at least M w 8.0 The Macquarie Fault Zone/Ridge extends south of New Zealand on the South Pacific Ocean 's seafloor except where it surfaces as Macquarie Island . Some of it is on Tasman Sea sea floor, north of the line between

1430-468: The adakitic Little Solander Island volcanics to the zone's far east to about 50,000 years ago suggests back arc activity from the subducted oceanic crust in the northern part of the zone may not have ceased. A northern sea mount of the McDougall Fault Zone is 10.9 ± 0.26 million years old while at the southern end there is one dated at 18.34 ± 0.53 million years old. A sea mount at the north of

1485-468: The Earth's subsurface. Transform faults specifically accommodate lateral strain by transferring displacement between mid-ocean ridges or subduction zones. They also act as the plane of weakness, which may result in splitting in rift zones . Transform faults are commonly found linking segments of divergent boundaries ( mid-oceanic ridges or spreading centres). These mid-oceanic ridges are where new seafloor

1540-457: The Earth's surface. Geophysicist and geologist John Tuzo Wilson recognized that the offsets of oceanic ridges by faults do not follow the classical pattern of an offset fence or geological marker in Reid's rebound theory of faulting , from which the sense of slip is derived. The new class of faults, called transform faults, produce slip in the opposite direction from what one would surmise from

1595-709: The Jurassic dolerite in Tasmania has been recovered by dredging from the centre of the South Tasman Rise on RV Rig Seismic on its cruise 147. Glomar Challenger drilled a borehole on the southern slope of STR. Hole 280 in oceanic crust resulted in basaltic intrusive of age 64.2 Ma. The hole at site 281 resulted in Precambrian quartz mica schist. RV Sonne did a cruise titled SO-36B in 1985 which did seismic profiles. Bottle green coloured microtectites were found in borehole 1169 at around early Pliocene age, 202.14 meters below

1650-527: The Pacific plate interacting with an area of the Indo-Australian plate termed the Macquarie microplate that has rotated independent of the Australian plate starting 6.24 million years ago. The best fit modelling of recent tectonics requires this microplate and there is evidence for a diffuse zone of deformation associated with compression between this microplate and the Australian plate but this diffuse zone

1705-661: The San Andreas Continental Transform-Fault system was created. In New Zealand , the South Island 's Alpine Fault is a transform fault for much of its length. This has resulted in the folded land of the Southland Syncline being split into an eastern and western section several hundred kilometres apart. The majority of the syncline is found in Southland and The Catlins in the island's southeast, but

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1760-505: The South Tasman Rise. A quartz syenite sample has an age of 1119 Ma which is Grenville in age. This kind of rock resembles rocks from the Grenville magmatic province in the west of the United States. It supports the idea that Laurentia and eastern Australia, including the South Tasman Rise were once joined to each other during the time of the Rodinia supercontinent . Dolerite similar to

1815-456: The constancy is caused by the continuous growth by both ridges outward, canceling any change in length. The opposite occurs when a ridge linked to a subducting plate, where all the lithosphere (new seafloor) being created by the ridge is subducted, or swallowed up, by the subduction zone. Finally, when two upper subduction plates are linked there is no change in length. This is due to the plates moving parallel with each other and no new lithosphere

1870-612: The continental crust of Zealandia . This north Macquarie Ridge Complex has to its west the Resolution Ridge which separates the oceanic crust of the north and south Tasman basins and defines the western margin of the Macqurie Block. The southern part of the Macquarie Ridge Complex is the Hjort Trench which also has a ridge to its east. Some authors split the central part of the Macquarie Ridge Complex into two central segments where

1925-563: The different relative heights of the abutting plates as well as the component of compression between the plates. The namesake Macquarie Island , named after Lachlan Macquarie lies atop a segment of the Macquarie Ridge. The Australia-Pacific plate boundary is now understood to be along the crest of the ridges rather than in the troughs with a zone of deformation up to 100 km (62 mi) wide. This central area has had up to 290 km (180 mi) right lateral displacement since ocean floor spreading ceased at about 10 million years ago. In

1980-625: The far south subduction is possibly initiating at the Hjort Trench. However this subduction has been described as atypical as lighter oceanic crust generated from the Southeast Indian Ridge is subducted under heavier oceanic crust from the extinct spreading center of the Australia-Pacific plate, where as normal subduction has the heavier component going under. This regions previous tectonic evolution has also been studied in detail as it

2035-442: The fault changes from a normal fault with extensional stress to a strike-slip fault with lateral stress. In the study done by Bonatti and Crane, peridotite and gabbro rocks were discovered in the edges of the transform ridges. These rocks are created deep inside the Earth's mantle and then rapidly exhumed to the surface. This evidence helps to prove that new seafloor is being created at the mid-oceanic ridges and further supports

2090-416: The fault zone here is an incipient subduction zone, with oblique motion corresponding to the transition from lateral (strike-slip) motion. In the area known as the Puysegur Trench , the Indo-Australian plate appears to be starting to sink beneath the Pacific plate, the reverse of what is occurring off of New Zealand's North Island (see Kermadec-Tonga Subduction Zone ). The Macquarie Ridge represents both

2145-592: The introduction of Arrangement Between the Government of Australia and the Government of New Zealand for the Conservation and Management of Orange Roughy on the South Tasman Rise . This agreement set a research target of 150 tonnes per country, intended to input data to scientific research on the fish population structure. Australian fishermen were allowed to catch three times as much fish as the New Zealanders. The quota

2200-813: The mid-oceanic ridge transform zones are in the Atlantic Ocean between South America and Africa . Known as the St. Paul, Romanche , Chain, and Ascension fracture zones, these areas have deep, easily identifiable transform faults and ridges. Other locations include: the East Pacific Ridge located in the South Eastern Pacific Ocean , which meets up with San Andreas Fault to the North. Transform faults are not limited to oceanic crust and spreading centers; many of them are on continental margins . The best example

2255-505: The other continent. In his work on transform-fault systems, geologist Tuzo Wilson said that transform faults must be connected to other faults or tectonic-plate boundaries on both ends; because of that requirement, transform faults can grow in length, keep a constant length, or decrease in length. These length changes are dependent on which type of fault or tectonic structure connect with the transform fault. Wilson described six types of transform faults: Growing length: In situations where

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2310-451: The ridge is to the west and the trench is to the east. Slightly confusingly the 5,500 m (18,000 ft) deep McDougall Trough is the trench to the east of the ridge of the Macquarie Fault Zone, with the other northern fault zone to the troughs north being named the McDougall Fault Zone. The trough has a step over basin to the Macquarie Fault Zone which commences where the Jurru fault zone in

2365-466: The seabed. Ocean Drilling Program Leg 189 made a borehole into the sediments termed Site 1171. Site 1169 was drilled at 145°14.2′E, 47°3.9′S. The rise forms a sector of an international fishery managed by Australia and New Zealand . New Zealand ceased fishing the area in the 2000-01 fishing season. By agreement between New Zealand and Australia the zone has been closed to commercial fishing since 2007. The principal species of fish sought after are

2420-444: The seafloor. A paper written by geophysicist Taras Gerya theorizes that the creation of the transform faults between the ridges of the mid-oceanic ridge is attributed to rotated and stretched sections of the mid-oceanic ridge. This occurs over a long period of time with the spreading center or ridge slowly deforming from a straight line to a curved line. Finally, fracturing along these planes forms transform faults. As this takes place,

2475-499: The segments accommodated the two plates convergence by oceanic-oceanic subduction at the southern Hjort segment and at the northern Puysegur segment and by predominant strike-slip motion in the two central segments of the Macquarie Ridge structure. Maps of this tectonic activity have been modelled from 42 million years ago to the present showing the evolving spreading center, its extinction and fault zone relationships. Transform fault A transform fault or transform boundary ,

2530-402: The smaller definition of the Macquarie Fault Zone is 14.1 ± 1.2 million years old and one beyond Macquarie Island to its south is 25.82 ± 0.18 million years old. Macquarie Island itself has multiple ages in the relatively limited range from 10.34 to 10 million years ago. A seamount near the eastern far end of the Hjort Trench is 25.90 ± 0.23 million years old. The Macquarie Fault Zone includes

2585-424: The source of some very large earthquakes and up until 1993 at least 20 over M w 6.5 had been recorded. The currently seismically active area is the whole of the zone and parts to the west of its northern aspects in the northern South East Tasman Basin. However both west of Macquarie Island and to its east towards the southern tip of the Campbell Plateau there has been some historic earthquake activity outside

2640-408: The south and possibly as recently as 1.6 million years ago near New Zealand. However it is known from elsewhere that basalt eruptions can continue for up to 3.5 million years after spreading stops so sea floor spreading in the north actually likely stopped sometime between 5 million and 1.6 million years ago if the single seamount sampled to date in this region is of mid oceanic ridge origin. And so to

2695-652: The south of the Auckland Islands and Tasmania . To its west on the sea floor is the South East Tasman Basin and to its east the Solander Trough and Emerald Basin. Technically the plate boundary becomes part of the Emerald Fracture Zone to the south of the Hjort Trench, so the zone does not quite reach the Macquarie triple junction. The Macquarie Fault Zone term is also used often now to refer to

2750-443: The southern Tasman Basin intercepts the plate boundaries. In the middle of the Macquarie Fault Zone is Macquarie Island . Its rocks like that of all the zone are mid-ocean ridge basalt or ocean island basalt . The central part of Macquarie Ridge Complex has a maximum height of 433 m (1,421 ft) at Macquarie Island but the troughs to the east drop to 6,000 m (20,000 ft) below sea level. At Macquarie Island which

2805-634: The standard interpretation of an offset geological feature. Slip along transform faults does not increase the distance between the ridges it separates; the distance remains constant in earthquakes because the ridges are spreading centers. This hypothesis was confirmed in a study of the fault plane solutions that showed the slip on transform faults points in the opposite direction than classical interpretation would suggest. Transform faults are closely related to transcurrent faults and are commonly confused. Both types of fault are strike-slip or side-to-side in movement; nevertheless, transform faults always end at

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2860-408: The theory of plate tectonics. Active transform faults are between two tectonic structures or faults. Fracture zones represent the previously active transform-fault lines, which have since passed the active transform zone and are being pushed toward the continents. These elevated ridges on the ocean floor can be traced for hundreds of miles and in some cases even from one continent across an ocean to

2915-510: The zone. In the Hjort Trench region the plate boundary is definitely under the stress condition of transpression as earthquake focal mechanisms are both thrust and dextral strike-slip types as found in such areas. To the south of the Hjort Trench there is relatively low grade seismic activity in the Emerald Fault Zone and towards the Macquarie triple junction. The largest strike-slip event till then on record occurred May 23, 1989, and had

2970-636: Was made in 2000 about the orange roughy fishery. One feature of this new agreement was a 2:1 payback for over fishing: if the country's quota was exceeded, it had to pay back via a double reduction in its future fish allowance. The South Tasman Rise Commonwealth Marine Reserve was declared in 2007. The reserve seeks to protect unique environments for marine life which are of significant scientific interest. 47°30′S 148°00′E  /  47.500°S 148.000°E  / -47.500; 148.000 Macquarie-Balleny Ridge The 1,600 kilometres (990 mi) long Macquarie Fault Zone (also known as

3025-537: Was set at 2100 and then 2400 tonnes for 1999-2000. However it was exceeded so the fishing ground was closed till the end of February 2000. In June 1999 fishing boats from South Africa and one registered in Belize came in to fish the rise outside of the bilateral agreement. Diplomatic pressure from Australia caused the Belize government to deregister its vessel and for the South Africans to withdraw their boats. A new agreement

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