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 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
thumb|The Pleiades in south east of map
The Pleiades are located at the crest of the Transantarctic Mountains, away from the coast of Lady Newnes Bay, Ross Sea. The volcanoes are located between Evans Neve and the beginning of Mariner Glacier, southeastwards towards the Ross Sea.
The volcanic group is formed by at least 12 steep, small volcanic cones and lava domes that emerge from the ice of Evans Neve over a long area. Most are nameless with the exception of the central Taygete Cone, Alcyone Cone just south of Taygete and the pair of high Mount Pleiones and c. high Mount Atlas in the southern sector. Mount Atlas and Mount Pleiones form a compound stratovolcano which is the principal volcano of The Pleiades Mount Atlas is formed by three separate cones that rise above the ice. Dykes, lava and scoria flows are found on these cones, the youngest of which has a semicircular crater. The summit of Mount Pleiones features nested craters. The distribution of the cones may mark the edges of a buried caldera.
Alcyone Cone lies north of Mount Atlas. Apart from the lava flows which make up most of Mount Atlas, pyroclastic rocks have been encountered at The Pleiades.
The volcanoes have alternatively been described as eroded An aeromagnetic anomaly has been correlated to the volcano group. The cones form an arcuate alignment that might reflect the existence of a wide caldera to their southeast.
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. Earlier volcanic activity began during the Cretaceous, when the West Antarctic Rift System became active.
The crust under the volcanic field is about thick. 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 and roughly follows the path of the Mariner Glacier, The Pleiades are located on the Bowers Terrane.
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, different depths or through fractional crystallization. Overall, these volcanic rocks define one of the most complete magmatic series of the McMurdo Volcanic Group. It is possible that the volcanoes first erupted trachyte and later basalts, and are distinct between the sodic and potassic rocks. 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. The Pleiones-Atlas complex may have last erupted 20,000 ± 7,000 years ago. yielding peculiar magmas that underwent intense crystal fractionation and absorbed large quantities of crustal material. When ice loads decreases, the evolved magmas rise to the surface.
Tephra deposits have been found in Antarctica which may originate at The Pleiades. These include:
- Eemian-age tephras in Taylor Glacier and Talos Dome, although some of the latter may originate at Mount Rittmann instead.
- One tephra layer emplaced about 50,000 years ago at a blue-ice area at Frontier Mountain.
- Several tens of thousands of years old tephra layers at Lewis Cliff/Beardmore Glacier probably originate at The Pleiades.
- 26,00022,000 years old tephra in the Ross Sea, which was emplaced when part of the Ross Sea was ice-free.
- 16,00015,000 years old tephra layers in Talos Dome.
- Tephra layers at Hercules Neve and Talos Dome, of probably Holocene age.
- A volcanic glass layer at Siple Dome dated to 12861292 AD. A tephra layer from 1254 AD was later correlated to Mount Rittmann.
- Tephras in ice cores that date to 17761885 AD, including one tephra layer at Siple Dome dated to about 1809.
- Finally, a major eruption may have occurred either at The Pleiades or at Mount Melbourne between 1880 and 1980.
The youngest ages of 6,000 ± 6,000 Presently, only minor fumarolic activity has been reported.
Features
Named geographical features include, from south to north:
- Mount Pleiones, , the southernmost and highest peak of The Pleiades. Named by the New Zealand Antarctic Place-Names Committee (NZ-APC) after Pleione of Greek mythology.
- Mount Atlas, , at the northeast side of Mount Pleiones. Named by the NZ-APC in association with Mount Pleiones after Atlas of Greek mythology.
- Alcyone Cone, , 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.
- Taygete Cone, , 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.
See also
- List of volcanoes in Antarctica