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37-610: The Havre Trough is characterised by a number of basins up to 3.7 km (2.3 mi) deep in the south, with several more shallow volcanic edifices that may rise to within 2.5 km (1.6 mi) of the ocean surface. It is a back-arc domain where rifting is universally oblique to the bounding ridges and consists of rifted horsts and grabens, extrusive magmatism and partially sedimented rifts. The western basins have flat floors and sediment in fills typically 0.4 km (0.25 mi) to 0.8 km (0.50 mi) thick consistent with little current extension activity. The thickest sediments in

74-420: A dramatic impact on life on Earth. The samples so far taken from the three plateaus are all consistent with ages of initial formation about 124 million years ago. There are, nevertheless, traces in seamounts on Hikurangi of a second Late Cretaceous magmatic event contemporaneous with volcanism on New Zealand and associated with the final break-up of Gondwana. The Hikurangi Plateau has been partly subducted under

111-492: A gravity anomaly, is now located more to the north being created between 350,000 and 2 million years and is about 70 kilometres (43 mi) wide. Consensus does not yet exist with regard to the cause of the Taupō Rift's extension or the exceptional volcanic productivity of the associated Taupō Volcanic Zone . Its geology and landforms are of worldwide interest, and it contains multiple significant faults and volcanoes, with some of

148-601: A more pronounced island arc basalt signature as one moves west to east towards the active volcanism of the Kermadec Ridge. At about 20°S the Australian Plate's crust is 10 km (6.2 mi) to 13 km (8.1 mi) thick which is thinner than the 16 km (9.9 mi) oceanic crust of the Kermadec Plate under the Kermadec Ridge. Further south the crust might thin to 5 km (3.1 mi) at

185-594: A relatively short geological timeframe. In the Bay of Plenty region the current active faults of the old Taupō Rift can align with those of the modern Taupō Rift. This was illustrated by the Edgecumbe Fault and the off sea White Island Fault in the Whakatāne Graben of the rift. The parallel Tauranga Fault Zone to the north represents a now mainly inactive old Taupō Rift margin. Further south, where more of

222-700: Is Mayor Island . Samples from the Rumble V Ridge are aged less than 110,000 years and the Ngatoro Rift have ages between 200,000 years and 680,000 years. The slightly more northern back arc Gill volcano which is towards the western area of the trough north of the Rumbles V Ridge has ages between 880,000 and 1.19 million years ago, while the Rapuhia Ridge, which extends southwest from the Rapuhia volcano in

259-583: Is between 15 mm (0.59 in)/year and 25 mm (0.98 in)/year, which should be viewed in context of the south to north trend of higher rates to the north and that the age of some basalt samples imply about a three times faster extension rate than this for the Havre Trough. Indeed, the Lau Basin to the north has extension rates that increase from 48 mm (1.9 in)/year to as much as 120 mm (4.7 in)/year at its north. The Lau Basin

296-555: Is compositional variation. Some are about the 5 million years of the arc ridges but most scattered across the trough are even younger. To date only two samples from the trough, close to the Colville Ridge, have any compositional relationship to the proto arc (Vitiaz Arc). However at 30°S in the middle of the trough a caldera volcano has been found that is rhyolitic , and erupted 52,000 year ago. The only other known example of alkali rhyolite in an active intraoceanic backarc basin

333-606: Is driven by oral tradition reports of hundreds dying in a relatively recent landslip on the Waihi Fault Zone south of Lake Taupō it may not be true. Certainly in the context that the Taupō Volcano has been responsible for the largest eruption of the last 30,000 years being the Oruanui eruption , and the more recent smaller 232 ± 10 CE Hatepe eruption but both eruptions occurred before human settlement,

370-438: Is found at about 36°S. The trough is less studied further from New Zealand. There is fair activity, especially in the eastern portion of the Havre Trough. At about 30°S there is a cluster of intermediate depth (200 km (120 mi) to 450 km (280 mi)) earthquakes reflecting seismology of the subducted slab. The volcanic dredged samples from within the trough are mainly basalts or basaltic andesites in contrast to

407-673: Is modelled as a spreading centre between the Manihiki Plate and the Hikurangi Plate which later became fixed components of today's Pacific Plate. A 2010 study of isotopic data supported the mega-plateau or " Greater Ontong Java Event " model. The study added several basins as remains of this LIP event, including the north-west part of the Central Pacific, Nauru, East Mariana, and Lyra basins — submarine volcanism that must have covered 1% of Earth's surface and had

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444-616: Is preserved. The modern Taupō Volcanic Zone started forming 61,000 years ago but the modern Taupō Rift appears to only have intra-rift fault activity after the immensely disruptive Oruanui eruption . Earthquake activity in the Taupo Rift exhibits the entire spectrum of behaviour ranging from large, ground rupturing events to swarm activity comprising thousands of small events. In the time since Māori settlement these larger earthquakes can be speculated to have resulted in more indirect loss of life than volcanic activity, although as this

481-777: Is separated from the Havre Trough by an intermediate uplifted region. This is north west of where the Louisville Ridge seamounts are being subducted under the Indo-Australian Plate. The Tonga-Kermadac Ridge volcanics are very active in this area north of the Monowai seamount . Two other prominent basins within the trough are the Ngatoroirangi Rift at 33.5°S, and the Rumble Rift at 35.5°S. The prominent Rumble V Ridge cross‐chain of arc volcanism

518-509: Is tectonic. The rift is in that part of the continental Australian Plate associated with the largely underwater Zealandia continental tectonic plate region. The rate of spread of the rift varies from effectively zero, at its southern inland end where the South Wanganui Basin is forming an initial back-arc basin, and volcanic activity has not yet begun, to in the Bay of Plenty as much as 19 mm (0.75 in)/yr. To

555-549: Is the seismically active rift valley containing the Taupō Volcanic Zone , central North Island of New Zealand . The Taupō Rift ( Taupo Rift ) is a 300 km (190 mi) intra-arc continental rift resulting from an oblique convergence in the Hikurangi subduction zone . The present young, modern Taupō Rift is defined by events between 25,000 and 350,000 years and the old Taupō Rift system, which can be defined by

592-688: The Chatham Rise , probably during the Cretaceous, and probably resulting in a slab more than 150 km (93 mi) long. The western margin of the plateau is actively subducting under the North Island of New Zealand to a depth of 65 km (40 mi). With these missing portions of the plateau added to it, the Hikurangi Plateau originally must have covered 800,000 km (310,000 sq mi), an area similar to that of

629-541: The Māhia Peninsula before crossing the plateau and ending in the South-west Pacific abyssal plain. Two models have been proposed for the formation of Hikurangi. It could be derived from the mantle plume that caused the break-up of Gondwana and the separation of Zealandia from Antarctica 107 Ma. Alternatively, it could have formed together with other Pacific plateaux around 120 Ma as part of

666-588: The Ontong Java - Manihiki -Hikurangi mega-plateau, in which case Hikurangi must have drifted thousands of kilometres during the Cretaceous silent period (84–121 Ma) before colliding with Gondwana. This later model (which does not exclude its initiation from a mantle plume) is the only one consistent with the current best fit Pacific Plate reference frame tectonics model where the Osbourn Trough

703-523: The Trans-Mexican Volcanic Belt result from a different tectonic process from the more studied intracontinental (intraplate) rifts it has been shown that the Taupō Rift displays all of the three modes of evolution. These are narrowing, lateral migration, and along-strike propagation, as found with intracontinental rifts. The Taupo Rift is widening much faster that other continental intraarc rifts, which might drive this evolution during

740-426: The andesite and dacite samples from the Kermadec Ridge arc front. This is consistent with the ambient mantle wedge under the Havre Trough being Pacific during its current rifting stage of backarc development. Basalts range from having almost no subduction influence, to significant influence at rear arc volcanoes. The oldest dredged samples are as expected over 100 million years old, but most are far younger and there

777-456: The Havre Trough are up to 1.5 km (0.93 mi) thick. There is no clear spreading ridge like those found in the Lau Basin. Magnetic anomaly mapping shows definite zones. However seismic sections show a buried ridge under the sediments. The eastern basins in the trough are shallower, and associated with evidence of active extension including little sedimentary cover, high heat flow, shallow seismicity, poorly defined magnetic zones and lavas with

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814-542: The Havre Trough between 28°S to 35°S. South of the Rapuhia Scarp at 35°S it is thought that the Hikurangi Plateau volcanics which are up to 15 km (9.3 mi) thick are subducting and this remnant of a Cretaceous Large Igneous Province changes erupted volcanic composition above it. It is now thought seafloor spreading at the Havre Trough started about 5.5 to 5.0 million years ago in response to

851-568: The Hikurangi Plateau slab suggests that it has played a significant role in the geology of New Zealand during the past 100 Ma. The Southern Alps in central South Island are being uplifted along the plate boundary there, a fault zone which parallels the western edge of the slab of the Hikurangi Plateau. The Australian and Pacific plates converge obliquely in the Tonga-Kermadec-Hikurangi subduction zone . The Hikurangi Plateau alters this subduction beneath North Island, at

888-680: The Manihiki Plateau 3,000 km (1,900 mi) to the north. The Hikurangi Plateau first subducted beneath New Zealand around 100 Ma during the Gondwana collision and it is currently subducting a second time as part of the convergence between the Pacific and Australian plates. These subducted parts are reaching 37–140 km (23–87 mi) into the mantle beneath the North Island and northern South Island . The extent of

925-552: The centre of the Havre Trough, so can be regarded as part of the rifting line has much younger ages of between 50,000 and 110,000 years ago. Four hundred and fifty miles to the north of the Gill volcano, in the western Harve Trough a basaltic volcanic sample was dated at 1.1 ± 0.4 Ma. Further there are three eastern Havre Trough dredged samples none of which is older than 150,000 years ago. The subducting Pacific plate lies between 170 km (110 mi) to 450 km (280 mi) beneath

962-575: The deepest basins. The most southern basin feature is the Ngatoro Rift at 36.5°S and comprising the trough's rifting tip which propagates the oceanic back‐arc into the New Zealand continental margin where it continues as the Taupō Rift and New Zealand's Taupō Volcanic Zone . The present active rifting is occurring in an area between the Colville Ridge and the Kermadec Ridge that at the most 15 km (9.3 mi) wide. The present rifting extension rate

999-543: The first part of the North Island to emerge from the ocean, gave its name to the plateau. The Hikurangi Plateau covers approximately 400,000 km (150,000 sq mi) and reaches 2,500–3,000 m (8,200–9,800 ft) below sea level. Hikurangi Plateau is cut by the Hikurangi Channel, a 2000 km abyssal channel that starts at Kaikōura and runs along the Hikurangi Trough as far as

1036-436: The north but in the south increase to up to 10 kilometres (6.2 mi) separation. There are breaks in the intra-rift fault systems in the recently active central rhyolitic caldera segments at the Taupō Volcano and Ōkataina Caldera. In the later case, the strike of the basaltic dyke of the 1886 eruption of Mount Tarawera follows that of faults to the south and north, confirming other hints that orientation of volcanism

1073-477: The north east it is related tectonically to the Havre Trough off the continental shelf which is also an active rift structure. The spread of the rift is associated with the basement graywacke rocks subsiding between the rift walls, so creating grabens infilled with volcanic deposits, sometimes from much higher volcanic mountains than the rift walls. Between 2016 and 2020 there was low volcanic activity in

1110-529: The old Taupō Rift faults appear to be inactive, the active and very complex Taupō Fault Belt is orientated north-north-east. This is trending with the modern Taupō Rift alignment, which is not always quite parallel with the old rift alignment. Beyond Lake Taupō to the south, there is a relatively narrow rifting segment in the Tongariro graben which considerably widens at the Ruapehu graben. South of Ruapehu

1147-592: The relative risk of earthquakes versus volcanoes depends upon time scale considered. Hikurangi Plateau The Hikurangi Plateau is an oceanic plateau in the South Pacific Ocean east of the North Island of New Zealand. It is part of a large igneous province (LIP) together with Manihiki and Ontong Java , now located 3,000 km (1,900 mi) and 3,500 km (2,200 mi) north of Hikurangi respectively. Mount Hikurangi , in Māori mythology

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1184-569: The rift except at Whakaari / White Island , and the areas of maximal satellite measured subsidence were confined to a small areas of about 30 mm (1.2 in)/year near the 2012 Te Māri eruptions site, or the rift geothermal power stations, while from Lake Taupō to the coast subsidence more usually peaked at about 15 mm (0.59 in)/year. The majority of the fault activity is normal faulting . While continental intraarc rifts such as this, and those associated with Mount Aso in Japan, and

1221-488: The rift, and its normal faulting, terminates with east to west faulting in the Taupō Rift termination faults . At the scale of the tectonic plate boundary, the rift trends NE-SW (41 ± 2°) but within New Zealand this trend is presently at 30° south of Lake Taupō and is 55° at the Bay of Plenty coast. A significant change in the mean fault strike occurs just south of the Ōkataina Caldera . The normal fault trends range from N20°E in

1258-436: The rollback of the subducting Pacific Plate and terminated abruptly about 3.0 to 2.5 million years ago In the western Havre Trough the evidence for historic seafloor spreading is believed to have resulted from the initial phase of extension after the break-up of the original proto-Colville-Kermadec arc (Vitiaz Arc). However rifting and volcanism is currently still active and some of the volcanic data suggests significant parts of

1295-459: The south to N45°E in the central and northern sectors. There is good evidence that the orientation of intra-arc strike and extension processes has been maintained for 4 million years in this region of New Zealand. The modern active rift ranges in width from 15 kilometres (9.3 mi) in the northern Bay of Plenty sector, to 40 kilometres (25 mi) beyond Lake Taupō . Significant faults may be separated by as little as 100 metres (330 ft) in

1332-555: The trough may only have formed of the order of a million years ago or less. This means the rate of spreading and thus recent tectonics will not be resolved without drill sampling and other studies. Whatever the eastern part of the trough is a young seismologically and volcanically active tectonic feature, but it is premature to think all the western part is older given the volcanic samples obtained to date. 30°42′S 179°24′W  /  30.7°S 179.4°W  / -30.7; -179.4 Taup%C5%8D Rift The Taupō Rift

1369-493: The volcanoes having potential for worldwide impact. The recent volcanism of the Taupō Volcanic Zone has been divided into three segments, with a central rhyolitic segment, dominated by explosive caldera associated with more typical Island Arc type andesite - dacite stratovolcanoes in either surrounding segment. In the hundreds of faults and their segments, some have associations with volcanism, but most fault activity

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