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.
Geography and geomorphology The Musicians Seamounts lie in the north-central Pacific, north of the Hawaiian Ridge north and northwest of Necker Island, extending over a length of 1,200 kilometres (750 mi). The seamounts were formerly known as the North Hawaiian Seamounts, or the North Hawaiian Seamount Range and were among the first submarine mountains to be thoroughly researched. 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. Such a ridge has been called a volcanic elongated ridge (VER). Seamounts have usually an elliptical cross section and heights of 1,000–4,000 metres (3,300–13,100 ft) 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). The ridges contain individual volcanoes and reach lengths of over 400 kilometres (250 mi); in the Italian 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. Larger than the seamounts are volcanic lineaments, on which the seamounts formed. Terrain observed by remotely operated vehicles shows large blocks, pillow lavas, flat terrain, lava flows and talus.
The name for the group was proposed in 1959. The total number of seamounts is about 65, some of which Henry William Menard named after 18th century musicians, and only about 25 are individually named. Among the seamounts known by name are:
Geology 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. To the north, the Musicians Seamounts are limited by the Pioneer fracture zone. and just to its south are four unnamed seamounts of the Northwest cluster. The Musicians Seamounts developed on crust that was no more than 20 million years old, and paleomagnetic information indicates that the seamounts were located between 0 and 10° north of the equator when they developed. Only several of the seamounts reached above sea level. 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, and manganese nodules have been encountered as well. The petrogenesis of Musicians Seamounts magmas has been explained by the mixing of several mantle-derived components.
Origin The origin of the seamounts has been explained with either one or two hotspots of Cretaceous age. Dating of the seamounts supports a hotspot origin only for the northwest–southeast trend, however. This hotspot has been named Euterpe hotspot after Euterpe, Greek Muse of musicians. 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. The oldest is a sample from one of the Northwest cluster at 98.1 Ma It is possible that their formation was influenced by the nearby presence of a spreading ridge, a process which has been suggested for other hotspots such as Réunion, Iceland, Azores and others as well. 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. This process is similar to that that formed the Wolf-Darwin linement extending from the present Galápagos hotspot. 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. Alternative earlier explanations for the formation of the Musicians Seamounts is the presence of a former spreading ridge at their site, 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.
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