The Pleiades (volcano group)
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The Pleiades are a volcanic group in northern Victoria Land of Antarctica. It consists of youthful cones and domes with Mount Atlas/Mount Pleiones, a small stratovolcano formed by three overlapping cones, being the dominant volcano and rising Template:Convert above the Evans Névé plateau. Two other named cones are Alcyone Cone and Taygete Cone, the latter of which has been radiometrically dated to have erupted during the Holocene. A number of tephra layers across Antarctica have been attributed to eruptions of this volcanic group, including several that may have occurred within the last few hundred years.
Geography and geomorphology
The Pleiades are located at the crest of the Transantarctic Mountains,<ref name="Stump 1986, p.305">Stump 1986, p.305</ref> Template:Convert<ref name="Kyle 1982, p.747">Kyle 1982, p.747</ref><ref name=":0">Faure and Mensing 2011, p.549</ref> away from the coast of Lady Newnes Bay, Ross Sea.<ref name="Kyle 1982, p.748">Kyle 1982, p.748</ref> The volcanoes are located between Evans Neve and the beginning of Mariner Glacier,<ref name=":0" /> which drains Evans Neve<ref>Riddolls and Hancox, 1968 p.882</ref> southeastwards towards the Ross Sea.<ref name="Kyle 1982, p.748"/> The volcanic group is named after the Pleiades star cluster in the constellation Taurus; the name was assigned to them by the New Zealand Geological Survey Antarctic Expedition.<ref>Template:Cite report</ref>
The volcanic group is formed by at least 12<ref>Rocchi et al. 2024, p.2</ref> steep,<ref name="Riddolls and Hancox, 1968 p.897">Riddolls and Hancox, 1968 p.897</ref> small volcanic cones and lava domes that emerge from the ice of Evans Neve<ref name="LeMasurier et al. 1990, p.60">LeMasurier et al. 1990, p.60</ref> over a Template:Convert long area. Most are nameless with the exception of the central Taygete Cone, Alcyone Cone just south of Taygete and the pair of Template:Circa Template:Convert high Mount Pleiones and c. Template:Convert high Mount Atlas in the southern sector.<ref name="Kyle 1982, p.749">Kyle 1982, p.749</ref> Mount Atlas and Mount Pleiones form a compound stratovolcano<ref name="Kim et al. 2019, p.120">Kim et al. 2019, p.120</ref> which is the principal volcano of The Pleiades<ref name="Stump 1986, p.305"/> and rises about Template:Convert above the ice.<ref>Rocchi et al. 2024, p.2</ref> Mount Atlas is formed by three separate cones that rise Template:Convert above the ice. Dykes, lava and scoria flows are found on these cones, the youngest of which has a semicircular crater.<ref name=":1"/> and scoria cones dot its flanks.<ref name="LeMasurier et al. 1990, p.60"/> At the foot of Mount Atlas are moraines with the form of ridges<ref name=":1"/> and there are moraines within one of its craters as well.<ref name="Smellie and Rocchi 2021, p.369">Smellie and Rocchi 2021, p.369</ref> The summit of Mount Pleiones features nested craters.<ref>LeMasurier et al. 1990, pp.60-62</ref> The distribution of the cones may mark the edges of a buried caldera.<ref>Rocchi et al. 2024, p.2</ref>
Alcyone Cone lies Template:Convert north of Mount Atlas.<ref name=":0" /> It is only slightly lower than Mount Atlas but is much smaller. It has two poorly defined craters and consists of lava flows covered with scree and volcanic bombs when not buried under snow.<ref name=":1" /> Taygete Cone Template:Convert north of Mount Atlas<ref name=":0" /> appears to be a lava dome bearing traces of hydrothermal alteration and of a small crater.<ref name=":1">Kyle 1982, p.750</ref> Apart from the lava flows which make up most of Mount Atlas,<ref name="Esser and Kyle 2002, p.415">Esser and Kyle 2002, p.415</ref> pyroclastic rocks have been encountered at The Pleiades.<ref name="Stump 1986, p.305"/> The other cones are partly buried by snow and some have breached or otherwise eroded craters.<ref name="Kyle 1982, p.751">Kyle 1982, p.751</ref>
The volcanoes have alternatively been described as eroded<ref name="Esser and Kyle 2002, p.415"/> or uneroded.<ref name="Stump 1986, p.305"/> The young appearance of the edifices indicates a young age of The Pleiades volcanoes.<ref name="Stump 1986, p.305"/> The volcanoes have been prospected for the possibility to generate geothermal energy but the presence of a good heat source is unlikely.<ref>Template:Cite book</ref> An aeromagnetic anomaly has been correlated to the volcano group.<ref>Template:Cite journal</ref> The cones form an arcuate alignment that might reflect the existence of a Template:Convert wide caldera to their southeast.<ref>Smellie and Rocchi 2021, p.368</ref>
Geology
The Pleiades belong to the McMurdo Volcanic Group and more specifically to the Melbourne volcanic province, which extends from Mount Melbourne to The Pleiades and Malta Plateau.<ref name="Stump 1986, p.305"/> These consist of the Cenozoic volcanoes of northern Victoria Land which form alignments and lineaments possibly controlled by deep fractures, and which are subdivided into a "Central Suite" consisting of large stratovolcanoes and a "Local Suite" consisting of other volcanic centres. Among the volcanoes of the McMurdo Volcanic Group are the large volcanoes Mount Overlord, Mount Melbourne<ref name="Kyle 1982, p.747"/> and in the area of The Pleiades the Malta Plateau.<ref name="Riddolls and Hancox, 1968 p.897"/> Volcanic activity began about 10Template:Spaced en dash space7 million years ago.<ref>Kyle 1982, p.752</ref> Earlier volcanic activity began during the Cretaceous, when the West Antarctic Rift System became active.<ref name="Kim et al. 2019, p.119">Kim et al. 2019, p.119</ref>
The crust under the volcanic field is about Template:Convert thick.<ref>Kim et al. 2023, p.2</ref> The basement underneath the volcanoes consists of Precambrian and Paleozoic sedimentary and intrusive rocks. The former are mostly represented by the Bowers Group/Bowers Supergroup and the Robertson Bay Group north of the volcanic complex and the latter by the Granite Harbour and Admiralty Intrusives mostly south of the volcanic complex. A major local fault system passes northeast of the volcanoes<ref name="Kyle 1982, p.748"/><ref name="Riddolls and Hancox, 1968 p.884">Riddolls and Hancox, 1968 p.884</ref> and roughly follows the path of the Mariner Glacier,<ref name="Riddolls and Hancox, 1968 p.884"/> while the Lanternman Fault passes southwest of them.<ref name="Kim et al. 2019, p.119"/> Some of these faults formed during the Ross Orogeny, when three terranes collided to form northern Victoria Land;<ref name="Kim et al. 2019, p.118">Kim et al. 2019, p.118</ref> The Pleiades are located on the Bowers Terrane.<ref name="Kim et al. 2019, p.119"/> Faults may also govern the position of The Pleiades volcanoes.<ref>LeMasurier et al. 1990, p.25</ref>
Composition
Basanite, basalt, benmoreite, hawaiite, phonolite, trachyandesite, trachyte and tristanite have been recovered from The Pleiades. These volcanic rocks define two separate sodium and potassium-rich magma suites and may originate from separate levels of the same magma chamber,<ref name="Kyle 1982, p.749,751">Kyle 1982, p.749,751</ref> different depths<ref name="Kim et al. 2023, p.3">Kim et al. 2023, p.3</ref> or through fractional crystallization.<ref name="Stump 1986, p.305"/> Ultimately, these magmas originate from a metasomatized mantle and were altered through assimilation of crustal material as they ascended.<ref>Kim et al. 2019, p.142</ref> Overall, these volcanic rocks define one of the most complete magmatic series of the McMurdo Volcanic Group.<ref>Stump 1986, p.335</ref> It is possible that the volcanoes first erupted trachyte and later basalts,<ref name="Kyle 1982, p.749,751"/> but later findings indicate that the two suites were erupted simultaneously.<ref name="Kim et al. 2019, p.118"/> Phenocrysts include anorthoclase, apatite, augite, biotite, kaersutite, magnetite, oligoclase and olivine,<ref>Stump 1986, p.306</ref> and are distinct between the sodic and potassic rocks.<ref name="Kim et al. 2023, p.3"/> Essexite,<ref name=":1"/> granodiorite,<ref name="Kyle 1982, p.748"/> granite and syenite xenoliths also occur.<ref name="Kyle 1982, p.751"/> Hydrothermal alteration at Taygete Cone has produced hematite and sulfur which coat and stain bleached trachyte.<ref name=":1"/>
Eruption history
The oldest dated rocks are 847,000 ± 12,000 years old.<ref name="Smellie and Rocchi 2021, p.369"/> Eruptions took place about 825,000 years ago and emplaced trachytes in the central part of the field; even older eruptions may have occurred but are now buried underneath of snow and ice. Three more eruptions occurred in the subsequent 700,000 years before activity began to increase after 100,000 years.<ref name="Esser and Kyle 2002, p.417">Esser and Kyle 2002, p.417</ref> Potassium-argon dating has yielded imprecise ages of 40,000 ± 50,000 for Mount Atlas and 20,000 ± 40,000 and 12,000 ± 40,000 for other volcanic cones.<ref name="Kyle 1982, p.749"/> Later argon-argon dating has yielded ages of less than 100,000 years for lavas on Mount Atlas<ref name="Esser and Kyle 2002, p.417"/> and for a lava east of Taygete, and ages of about 45,000 years for Alcyone and two more lava flows on Mount Atlas.<ref name="Esser and Kyle 2002, p.418">Esser and Kyle 2002, p.418</ref> The Pleiones-Atlas complex may have last erupted 20,000 ± 7,000 years ago.<ref name="Smellie and Rocchi 2021, p.369"/> Volcanic activity may have been influenced by ice load, which prevented the ascent of the magmas and allowed them to accumulate and evolve in the crust,<ref>Rocchi et al. 2024, p.13</ref> yielding peculiar magmas that underwent intense crystal fractionation and absorbed large quantities of crustal material.<ref>Template:Cite journal</ref> When ice loads decreases, the evolved magmas rise to the surface.<ref>Rocchi et al. 2024, p.15</ref>
Tephra deposits have been found in Antarctica which may originate at The Pleiades. These include:
- Eemian-age tephras in Taylor Glacier<ref>Template:Cite journal</ref> and Talos Dome, although some of the latter may originate at Mount Rittmann instead.<ref>Template:Cite journal</ref>
- One tephra layer emplaced about 50,000 years ago at a blue-ice area at Frontier Mountain.<ref>Template:Cite journal</ref>
- Several tens of thousands of years old tephra layers at Lewis Cliff/Beardmore Glacier probably originate at The Pleiades.<ref>Template:Cite journal</ref>
- 26,000Template:Spaced en dash space22,000 years old tephra in the Ross Sea, which was emplaced when part of the Ross Sea was ice-free.<ref>Template:Cite journal</ref>
- 16,000Template:Spaced en dash space15,000 years old tephra layers in Talos Dome.<ref>Template:Cite journal</ref>
- Tephra layers at Hercules Neve and Talos Dome, of probably Holocene age.<ref>Template:Cite journal</ref>
- A volcanic glass layer at Siple Dome dated to 1286Template:Spaced en dash space1292 AD.<ref>Template:Cite report</ref> A tephra layer from 1254 AD was later correlated to Mount Rittmann.<ref>Lee et al. 2019, p.174</ref>
- Tephras in ice cores that date to 1776Template:Spaced en dash space1885 AD,<ref>Template:Cite journal</ref> including one tephra layer at Siple Dome dated to about 1809.<ref>Template:Cite journal</ref>
- Finally, a major eruption may have occurred either at The Pleiades or at Mount Melbourne between 1880 and 1980.<ref name="autogenerated7431">Template:Cite journal</ref>
The youngest ages of 6,000 ± 6,000<ref name="Esser and Kyle 2002, p.418"/> and 3,000 ± 14,000 years ago have been obtained on Taygete,<ref name="Kyle 1982, p.749"/> which together with the youthful texture of this dome<ref name="Kim et al. 2019, p.120"/> indicates a young age for The Pleiades, despite the imprecise dates.<ref name=":1"/> The presence of pumice lapilli has been taken as evidence of very recent activity in the form of a moderate pumice eruption.<ref>LeMasurier et al. 1990, p.51</ref> Presently, only minor fumarolic activity has been reported.<ref name="autogenerated7431"/> Future eruptions are possible<ref name="Esser and Kyle 2002, p.418"/> and The Pleiades are not monitored, but they are also remote from any research station.<ref>Lee et al. 2019, p.175</ref>
Features
Template:GeoGroup Named geographical features include, from south to north:
- Template:Anchor Mount Pleiones, Template:Coord, the southernmost and highest peak of The Pleiades. Named by the New Zealand Antarctic Place-Names Committee (NZ-APC) after Pleione of Greek mythology.Template:Sfn
- Template:Anchor Mount Atlas, Template:Coord, at the northeast side of Mount Pleiones. Named by the NZ-APC in association with Mount Pleiones after Atlas of Greek mythology.Template:Sfn
- Template:Anchor Alcyone Cone, Template:Coord, near the center of The Pleiades. Named by a Victoria University of Wellington Antarctic Expedition (VUWAE) field party to Evans Névé, 1971–72, after Alcyone, the brightest star in the Pleiades constellation.Template:Sfn
- Template:Anchor Taygete Cone, Template:Coord, northeast of Alcyone Cone in the north part of The Pleiades. Named by the NZ-APC after Taygete (Taygeta), one of the stars in the Pleiades.Template:Sfn