Gaussberg (orSchwarzen Berg,[3]Mount Gauss) is a 370-metre-high (1,210-foot) extinctvolcanic cone inEast Antarctica fronting onDavis Sea immediately west ofPosadowsky Glacier. It is ice-free and conical in nature, having formedsubglacially about 55,000 years ago. The current edifice is thought to be the remains of a once-largermountain that has been reduced byglacial andsubaerialerosion. The volcano has producedlamproite magmas, and is the youngest volcano to have produced such magmas on Earth.
Owing to its peculiar composition, Gaussberg has been intensively researched.[6] The mountain was investigated in 1912 by the 1911-1914Australasian Antarctic Expedition, by theSoviet Antarctic Expedition in 1956–1957,[4] by Australian expeditions in 1977, 1981,[7] 1987[8] and by an expedition linked to an entity "K.D.C" in 1997.[9] Regionalkrill stocks in turn were named after the mountain.[10] Owing to its peculiar composition and isolated location, the volcano has an importance out of proportion to its actual size.[11] The mineralgaussbergite is named after the volcano.[12]
It consists of a 370-metre-high (1,210-foot), 1.5-kilometre-wide (0.93-mile)[1] cone located between theEast Antarctic Ice Sheet on three sides and the sea on the fourth.[16] It is the onlyexposure of rock in the region,[16][17] with rocky outcrops at the summit and on the northern flank.[18] The edifice covers an area of about 10 square kilometres (3.9 sq mi)[19] and has a volume of 1 cubic kilometre (0.24 cu mi).[19] Most of the edifice is made out ofpillow lavas with radii of 0.5–2 metres (1 ft 8 in – 6 ft 7 in) and 3–5 centimetres (1.2–2.0 in) thick crusts. The volcano is covered with lava fragments resemblinglapilli which may have formed through erosion. Gaussberg has novolcanic crater,[4] rather having a ridge at the summit. The volcano has several terraces of undetermined origin[16] and may have formed as ashield volcano with multiple vents.[11] The rocks were probably emplaced subglacially, although the occurrence ofpahoehoe lava is possible.[20] There aremoraines on the southern, northwestern and northeastern foot of the volcano,[18] anderratic blocks andglacial striations are evidence that the volcano was formerly glaciated.[21]
Gaussberg is an extremely isolated volcano[22] although anice rise a few kilometres southwest of Gaussberg[23] andaeromagnetic surveys suggest that within 30 kilometres (19 mi) there are other small volcanoes in the area.[11] It is the only Antarctic volcano situated on theAntarctic Shield, where the thickestcrust of Antarctica is found.[24] Why it formed about 50,000 years ago on a stable continental margin is unclear; either amantle plume, an instability of the East Antarctic continent[25][26][27] or lateral flow of mantle plume material are possible.[28] Thebasement underneath Gaussberg is formed bygneisses ofArchean toProterozoic age.[19] Thelithosphere under Gaussberg is over 150 kilometres (93 mi) thick[26] and has an unusually highheat flow.[29]
Its activity has been related to theKerguelen Plateau, but the Kerguelen volcanoes have yielded different magma compositions and there is no major geological structure linking the two other than the so-called "Kerguelen-Gaussberg Ridge",[22] thus a connection between the two is unproven.[17] Agraben system in the region, which may have formed inGondwana and may be correlated to tectonic structures on theIndian Peninsula, has been christened the "Gaussberg Rift";[30] the volcano rises on ahorst on the rift but its relation to the rift is unclear.[31] Finally, the 90° EFault that separates regional tectonic structures may have influenced volcanism at Gaussberg.[32]
The source of the Gaussberg lamproites is unclear, as the processes usually proposed for the formation of such magmas do not easily apply to the Gaussberg rocks.[40] The magma may have formed through the incomplete melting ofphlogopite-richmantle and further chemical processes such ascrystal fractionation that raised the potassium/aluminium ratio above 1.[41] Deep mantle structures that formed throughsubduction billions of years ago and remained isolated since then have been proposed as the source of Gaussberg lamproites.[40] TheKerguelen plume may[42] or may not have played a role.[11]
Drastically different age estimates have been obtained on Gaussberg. Early research suggested aPliocene orMiocene age based on a presumed history of the Antarctic Ice Sheet and comparisons between the appearance of Gaussberg with Kerguelen volcanoes.[33]Potassium-argon dating has yielded ages of 20 and 9 million years,[22] with younger dating efforts producing an age of 56,000±5,000 years.[43]Fission track dating produced ages of 25,000±12,000 years and geomorphologic considerations support a latePleistocene age.[22] These disagreements between potassium-argon dating and other dating methods may indicate either contamination with older rocks or the presence of non-outgassedargon.[33] The 56,000±5,000 years age is considered to be more probable than the 20 and 9 million years ones.[44]
Gaussberg was probably constructed in a single eruptive episode[45] but there is evidence that the present-day edifice formed on an older, eroded volcano.[36] Gaussberg formed under much thicker ice than there is today in the area, and the ice deposited moraines on its summit.[22] There are different views on how erosion affected Gaussberg; some think that it was largely spared[46] and others that erosion wore down the initially much larger edifice to its current size;[47][9] the latter theory is the preferred view of theGlobal Volcanism Program[48] and is supported by aeromagnetic data which suggest an initial size of 10 kilometres (6.2 mi).[11] Dust layers in theSiple Domeice core may come from wind-driven erosion of Gaussberg rocks.[49]
