Musicians Seamounts | |
---|---|
North Pacific Ocean | |
Location | |
Location | North Pacific Ocean |
Coordinates | 30°N162°W / 30°N 162°W [1] |
Geology | |
Volcanic arc/chain | Euterpe Hotspot |
Age of rock | |
Last eruption | 47.4 Ma |
Musicians Seamounts (previously North Hawaiian Seamounts, North Hawaiian Seamount Range) are a chain of seamounts in the Pacific Ocean, north of the Hawaiian Ridge. There are about 65 seamounts, some of which are named after musicians. These seamounts exist in two chains, one of which has been attributed to a probably now-extinct hotspot called the Euterpe hotspot. Others may have formed in response to plate tectonics associated with the boundary between the Pacific plate and the former Farallon plate.
The seamounts were constructed on young oceanic crust during the Cretaceous, but a second phase of volcanic activity took place during the Eocene. Deep sea coral reefs occur on the seamounts.
The Musicians Seamounts lie in the north-central Pacific, [3] [4] north of the Hawaiian Ridge north and northwest of Necker Island, [5] extending over a length of 1,200 kilometres (750 mi). [6] The seamounts were formerly known as the North Hawaiian Seamounts, [7] or the North Hawaiian Seamount Range [8] and were among the first submarine mountains to be thoroughly researched. [9]
The seamounts consist of two separate chains (one trending in north–south direction parallel to the Emperor Seamounts and the other in northwest–southeast direction parallel to the northern Line Islands) of ridges that extend east–west and seamounts. [4] Such a ridge has been called a volcanic elongated ridge (VER). [10] Seamounts have usually an elliptical cross section and heights of 1,000–4,000 metres (3,300–13,100 ft) [3] and no flat tops like other seamounts south of the Hawaiian Ridge; the highest is Liszt Seamount whose summit has a depth of 1,582 metres (5,190 ft). [11] The ridges contain individual volcanoes and reach lengths of over 400 kilometres (250 mi); in the Italian [a] and Rapano (Bach) Ridges the volcanoes are 2.2–5.1 kilometres (1.4–3.2 mi) high. The Musicians horst and the Southern Ridges are additional features of the Musicians Seamounts. [1] Larger than the seamounts are volcanic lineaments, on which the seamounts formed. [13] Terrain observed by remotely operated vehicles shows large blocks, pillow lavas, flat terrain, lava flows and talus. [14]
The name for the group was proposed in 1959. [7] The total number of seamounts is about 65, [6] some of which Henry William Menard named after 18th century musicians, [15] and only about 25 are individually named. [7] Among the seamounts known by name are: [16] [5] [17] [18]
The Pacific Ocean floor beneath the seamounts is of Cretaceous age and is subdivided by the Murray Fracture Zone into an older northern (100 to 95 million years ago) and a younger southern (80 to 85 million years ago) sector. [4] To the north, the Musicians Seamounts are limited by the Pioneer fracture zone. [25] and just to its south are four unnamed seamounts of the Northwest cluster. [2] The Musicians Seamounts developed on crust that was no more than 20 million years old, [4] and paleomagnetic information indicates that the seamounts were located between 0 and 10° north of the equator when they developed. [26] Only several of the seamounts reached above sea level. [27]
Rock samples dredged from the seamounts include basalt, hawaiite, mugearite and trachyte. Minerals contained in the rocks consist of aegirine, augite, clinopyroxene, feldspar, oxidized olivine, orthopyroxene, plagioclase and pyroxene. Calcite, clay and zeolites have formed through alteration processes, [28] and manganese nodules have been encountered as well. [29] The petrogenesis of Musicians Seamounts magmas has been explained by the mixing of several mantle-derived components. [30]
The origin of the seamounts has been explained with either one or two hotspots of Cretaceous age. [4] Dating of the seamounts supports a hotspot origin only for the northwest–southeast trend, however. [26] This hotspot has been named Euterpe hotspot after Euterpe, Greek Muse of musicians. [1] Plate reconstructions for the time period based on the dates of the northwest–southeast trend and the older Line Islands are consistent with each other. [31] The oldest is a sample from one of the Northwest cluster at 98.1 Ma [2]
It is possible that their formation was influenced by the nearby presence of a spreading ridge, [32] a process which has been suggested for other hotspots such as Réunion, Iceland, Azores and others as well. [33] The Pacific-Farallon Ridge was located east of the Musicians Seamounts and flow from the hotspot to the ridge may have generated the east–west trending VERs of the Musicians Seamounts. [1] This process is similar to that that formed the Wolf-Darwin linement extending from the present Galápagos hotspot. [10] Technically this could be explained in plate tectonics as a process of asthenosphere related flow allowing buoyant melt from the hotspot being channelled towards the active spreading center. [10]
Alternative earlier explanations for the formation of the Musicians Seamounts is the presence of a former spreading ridge at their site, [25] and crustal weaknesses associated with the so-called "bending line" in the region which was formed by a change in the motion of the Pacific plate. [34]
The Musicians Seamounts were active during the Late Cretaceous. [4] Ages obtained on some seamounts range from 96 million years ago for one that is unnamed in the Northwest Cluster, to 47 million years ago. [19] The ages include over 94 million years ago for Hammerstein, 91 million years ago for Mahler, 90 million years ago for Brahms, 86 million years ago for Rachmaninoff, 84 million years ago for Liszt, 83 million years ago for Khatchaturian and West Schumann, 82 million years ago for West Mendelssohn, 79 million years ago for East Mendelssohn, 75 million years ago for Bach Ridge and Haydn to 65 million years ago for Paumakua. [16]
Based on considerations derived from plate tectonics, earlier volcanism could have occurred on the Farallon plate, [1] which has been subducted in its entirely and its volcanoes have now vanished. [35] No volcanism in the Musicians Seamounts post-dating about 70 million years ago was discovered at first; [26] either volcanism ceased at that time or it continued on the Farallon plate again. [32] The Euterpe hotspot is now extinct, [d] [1] although an unusually shallow ocean region around 0°S148°W / -0°N 148°W may be a remnant of the Euterpe hotspot. [36]
Some of the ridges in the Musicians Seamounts have much younger ages, 53 to 52 million years ago by argon-argon dating [37] and continuing to 48 to 47 million years ago. [38] This volcanism occurred at the time of major changes in the motion of the Pacific plate; stresses occurring within the plate may have reactivated the Musicians volcanoes and resulted in this late stage activity. [39] One earthquake has been recorded in the province during historical time. [40]
About 10,000 seamounts and islands are estimated to dot the floor of the Pacific Ocean, forming clusters and chains. [41] The origin of chains of seamounts and islands is commonly explained with the hotspot hypothesis, which posits that as the crust migrates above a stationary hotspot volcanism forms these structures. A further hypothesis, which is known now to be an approximation, supposed that the hotspots, sourced from mantle plumes, are static with respect to each other and thus geologists can reconstruct the history of plate movement by analyzing the tracks traced on the crust by hotspots. [42] Later tectonic therapy allows for mantle plume shifts. [2]
The Pacific Ocean contains a number of seamount and island chains, [42] some of which have been attributed to hotspots such as the Cobb hotspot, Caroline hotspot, Hawaiian hotspot, Marquesas hotspot, Tahiti hotspot, Pitcairn hotspot, Macdonald hotspot and Louisville hotspot. [4] Not all of these hotspots are necessarily fed by a deep continuous mantle plume; some may be nourished by discrete batches of melting material that rise through the mantle. [32] Other chains may be controlled by mantle flow towards a spreading ridge, which has been proposed for the Musicians chain, [43] as mentioned in the earlier VER discussion. [10]
The lithosphere that the Musicians seamounts formed on is known from magnetic data to be between 121.4 and 83.65 million years old (Cretaceous normal superchron, C34n) except for the easternmost tip of the southern VERs which is C33r so is somewhere between 83.65 and about 79 million years old. [44] It formed from ancient Pacific-Farallon plate spreading centers to the south-east of the Euterpe hotspot. [44] Pacific plate motion was stable in its general north-west vector from the initial formation of the Northwest Cluster, [45] and can be calculated to be 42 ± 9 km (26.1 ± 5.6 mi)/million years. [22] This constrains the early change in Pacific plate rotation pole (where before this the local Pacific plate direction of movement was towards the west) [45] to before 98 million years ago., [22] The seamount alignment in the southern chain bends at about 81 million age and this correlates with the 79 million years ago bend in the northern Hawaiian–Emperor seamount chain, just north of the Detroit Seamount. [22] After this the local vector direction of the Pacific plate was towards the north. [45] Other evidence has suggested that the next change in Pacific plate rotation poles was between 54 and 47 million years ago which may have allowed extension volcanism in the southern part of the chain. [46]
Deep sea corals and sponges grow on the Musicians Seamounts; [47] corals identified include Antipathes , Acanthogorgia , chrysogorgidae, Hemicorallium , isididae, Paracalyptrophora , Pleurogorgia and primnoids, while sponges include Caulophacus , Hyalostylus , Poliopogon and Saccocalyx . In some places true "coral forests" grow on the seamounts. [48] Very high-density sessile cnidaria communities are found on Mussorgsky Seamount, Beethoven Ridge and Rapano Seamount at about 2,000 m (6,600 ft). [48] On the Beethoven Ridge which is the deeper of these three at between 2,300 and 2,531 m (7,546 and 8,304 ft), the dominant species by far are anthomastus corals and the sponge density is also very high. [49] Mussorgsky Seamount is predominantly a community of Narella (35%), Primnoidae (20%) and Keratosidinae (15%) while Mendelssohn Seamount has almost a 75% Keratosidinae deep sea coral predominance. [49] Moderate sessile cnidaria density is present on Debussy Seamount, Paganini Seamount, Schumann Seamount, Mendelssohn Seamount, Wagner Seamount, Shostakovich Seamount and Sibelius Seamount. [49] Lower density communities tend to be found at the deeper seamounts such as Mozart 3,571–3,849 m (11,716–12,628 ft) and Verdi 3,008–3,092 m (9,869–10,144 ft). [49]
Animal species observed on the seamounts by remotely operated vehicles include amphipods, anemones, anglerfish, arrow worms, bristlemouths, brittle stars, cephalopods, chirons, codling fish, ctenophores, crinoids, cusk eels, fangtooth fish, halosaurs, jellyfish, larvaceans, piglet squid, polychaetes, ribbon worms, sea cucumbers, sea elephants, sea pens, sea spiders, sea stars, shrimp, siphonophores, spider crabs, squat lobsters, urchins and zoanthids. [14]
The Galápagos hotspot is a volcanic hotspot in the East Pacific Ocean responsible for the creation of the Galápagos Islands as well as three major aseismic ridge systems, Carnegie, Cocos and Malpelo which are on two tectonic plates. The hotspot is located near the Equator on the Nazca Plate not far from the divergent plate boundary with the Cocos Plate. The tectonic setting of the hotspot is complicated by the Galápagos triple junction of the Nazca and Cocos plates with the Pacific plate. The movement of the plates over the hotspot is determined not solely by the spreading along the ridge but also by the relative motion between the Pacific plate and the Cocos and Nazca plates.
The Cobb-Eickelberg seamount chain is a range of undersea mountains formed by volcanic activity of the Cobb hotspot located in the Pacific Ocean. The seamount chain extends to the southeast on the Pacific Plate, beginning at the Aleutian Trench and terminating at Axial Seamount, located on the Juan de Fuca Ridge. The seamount chain is spread over a vast length of approximately 1,800 km. The location of the Cobb hotspot that gives rise to these seamounts is 46° N—130° W. The Pacific plate is moving to the northwest over the hotspot, causing the seamounts in the chain to decrease in age to the southeast. Axial is the youngest seamount and is located approximately 480 km west of Cannon Beach, Oregon. The most studied seamounts that make up this chain are Axial, Brown Bear, Cobb, and Patton seamounts. There are many other seamounts in this chain which have not been explored.
The Hawaiʻi hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the best known and intensively studied hotspots in the world, the Hawaii plume is responsible for the creation of the Hawaiian–Emperor seamount chain, a 6,200-kilometer (3,900 mi) mostly undersea volcanic mountain range. Four of these volcanoes are active, two are dormant; more than 123 are extinct, most now preserved as atolls or seamounts. The chain extends from south of the island of Hawaiʻi to the edge of the Aleutian Trench, near the eastern coast of Russia.
The Louisville hotspot is a volcanic hotspot responsible for the volcanic activity that has formed the Louisville Ridge in the southern Pacific Ocean.
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The Samoa hotspot is a volcanic hotspot located in the south Pacific Ocean. The hotspot model describes a hot upwelling plume of magma through the Earth's crust as an explanation of how volcanic islands are formed. The hotspot idea came from J. Tuzo Wilson in 1963 based on the Hawaiian Islands volcanic chain.
The Macdonald hotspot is a volcanic hotspot in the southern Pacific Ocean. The hotspot was responsible for the formation of the Macdonald Seamount, and possibly the Austral-Cook Islands chain. It probably did not generate all of the volcanism in the Austral and Cook Islands as age data imply that several additional hotspots were needed to generate some volcanoes.
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The Mid-Pacific Mountains (MPM) is a large oceanic plateau located in the central North Pacific Ocean or south of the Hawaiian–Emperor seamount chain. Of volcanic origin and Mesozoic in age, it is located on the oldest part of the Pacific Plate and rises up to 2 km (1.2 mi) above the surrounding ocean floor and is covered with several layers of thick sedimentary sequences that differ from those of other plateaux in the North Pacific. About 50 seamounts are distributed over the MPM. Some of the highest points in the range are above sea level which include Wake Island and Marcus Island.
Arago hotspot is a hotspot in the Pacific Ocean, presently located below the Arago seamount close to the island of Rurutu, French Polynesia.
Foundation Seamounts are a series of seamounts in the southern Pacific Ocean. Discovered in 1992, these seamounts form a 1,350 kilometres (840 mi) long chain which starts from the Pacific-Antarctic Ridge. Some of these seamounts may have once emerged from the ocean.
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Crough Seamount is a seamount in the Pacific Ocean, within the exclusive economic zone of Pitcairn. It rises to a depth of 650 metres (2,130 ft) and is paired with a taller but overall smaller seamount to the east. This seamount has a flat top and probably formed an island in the past. It is about 7-8 million years old, although a large earthquake recorded at its position in 1955 may indicate a recent eruption.
Limalok is a Cretaceous-Paleocene guyot/tablemount in the southeastern Marshall Islands, one of a number of seamounts in the Pacific Ocean. It was probably formed by a volcanic hotspot in present-day French Polynesia. Limalok lies southeast of Mili Atoll and Knox Atoll, which rise above sea level, and is joined to each of them through a volcanic ridge. It is located at a depth of 1,255 metres (4,117 ft) and has a summit platform with an area of 636 square kilometres (246 sq mi).
Lo-En or Hess is an Albian–Campanian guyot in the Marshall Islands. One among a number of seamounts in the Pacific Ocean, it was probably formed by a hotspot in what is present-day French Polynesia. Lo-En lies southeast of Eniwetok which rises above sea level, and Lo-En is almost connected to it through a ridge.
Pako Guyot is a guyot in the Pacific Ocean.
The Rarotonga hotspot is a volcanic hotspot in the southern Pacific Ocean. The hotspot is claimed to be responsible for the formation of Rarotonga and some volcanics of Aitutaki but an alternative explanation for these islands most recent volcanics has not been ruled out. Recently alternatives to hotspot activity have been offered for several other intra-plate volcanoes that may have been associated with the Rarotonga hotspot hypothesis.
Horizon Guyot is a presumably Cretaceous guyot (tablemount) in the Mid-Pacific Mountains, Pacific Ocean. It is an elongated ridge, over 300 kilometres (190 mi) long and 4.3 kilometres (2.7 mi) high, that stretches in a northeast–southwest direction and has two flat tops; it rises to a minimum depth of 1,443 metres (4,730 ft). The Mid-Pacific Mountains lie west of Hawaii and northeast of the Line Islands.
Allison Guyot is a tablemount (guyot) in the underwater Mid-Pacific Mountains of the Pacific Ocean. It is a trapezoidal flat mountain rising 1,500 metres (4,900 ft) above the seafloor to a depth of less than 1,500 metres (4,900 ft), with a summit platform 35 by 70 kilometres wide. The Mid-Pacific Mountains lie west of Hawaii and northeast of the Marshall Islands, but at the time of their formation were located in the Southern Hemisphere.
Vlinder Guyot is a guyot in the Western Pacific Ocean. It rises to a depth of 1,500 metres (4,900 ft) and has a flat top covering an area of 40 by 50 kilometres. On top of this flat top lie some volcanic cones, one of which rises to a depth of 551 metres (1,808 ft) below sea level. Vlinder Guyot has noticeable rift zones, including an older and lower volcano to the northwest and Oma Vlinder seamount south.