Napier Mountains
Encyclopedia
The Napier Mountains are a group of more-or-less separated peaks, the highest being Mount Elkins
, at about 2,300 meters above sea level. This mountain range
is located in Enderby Land
, in the claimed Australian Antarctic Territory
, East Antarctica
.
, the Napier Mountains are located roughly 4 degrees west of Cape Boothby
, Edward VIII Bay
and Edward VIII Ice Shelf
, and 3.5 degrees east of Amundsen Bay
. The Napier Mountains are centered about 64 km south of Cape Batterbee
in Enderby Land, East Antarctica. It extends about 64 km in a NW-SE direction from Mount Codrington
, and also includes Mount Kjerringa
, and the Young Nunataks
.
The Enderby Land Coast Ranges are considered to be a subset of their parent ranges, the Wilkes Land Coast Ranges
. The Wilkes Land Coast Ranges are, in turn, a subsidiary of their parent ranges, the East Antarctica Ranges
.
, 1924–42 and Chief Justice of South Australia, 1942-67. This mountain range was first visited by an ANARE party in 1960. Members of this party included Syd Kirkby and Terence James Elkins
.
s on Earth. Its evolution is characterized by high-grade metamorphism
and several strong deformations. At least four distinct tectonothermal events occurred in the Archaean Eon
:
Much of the East Antarctic craton
was formed in the Precambrian
period by a series of tectonothermal orogenic
events. Napier orogeny formed the cratonic nucleus approximately 4 billion years ago. Mount Elkins is a classic example of Napier orogeny. Napier orogeny is characterized by high-grade metamorphism
and plate tectonics
. The orogenic events which resulted in the formation of the Napier Complex (including Mount Elkins) have been dated to the Archean
Eon
. Radiometrically dated
to as old as 3.8 billion years, some of the zircon
s collected from the orthogneisses
of Mount Sones
are among the oldest rock specimens found on Earth. Billions of years of erosion
and tectonic deformation
have exposed the metamorphic rock
core of these ancient mountains.
The oldest crustal
components found to date in the Napier Complex appear to be of igneous
derivation. This rock appears to have been overprinted by an ultra-high temperature metamorphic event (UHT) that occurred near the Archean-Proterozoic boundary. Using a lutetium-hafnium
(Lu-Hf) method to examine garnet
, orthopyroxene
, sapphirine
, osumilite
and rutile
from this UHT granulite
belt, Choi et al determined an isochron
age of 2.4 billion years for this metamorphic event. Using SHRIMPU–Pb zircon dating methodology, Belyatsky et al determined the oldest tectonothermal event in the formation of the Napier Complex to have occurred approximately 2.8 billion years ago.
Preservation of the UHT mineral assemblage in the analyzed rock suggests rapid cooling, with closure likely to have occurred for the Lu-Hf system at post-peak UHT conditions near a closure temperature
of 800°C. UHT granulites appear to have evolved in a low Lu-Hf environment, probably formed when the rocks were first extracted from a mantle
profoundly depleted in lithophile elements. The source materials for the magma
s that formed the Napier Complex were extremely depleted relative to the chondritic uniform reservoir (CHUR). These results also suggest significant depletion of the early Archean mantle, in agreement with the early igneous differentiation
of the Earth that the latest core formation models require.
Mount Elkins
Mount Elkins, also known as Jökelen is a dark, steep-sided mountain with three major peaks, the highest 2,300 metres above sea level. This peak is located in the Napier Mountains, in Enderby Land. Enderby Land is part of the Australian Antarctic Territory, in East Antarctica...
, at about 2,300 meters above sea level. This mountain range
Mountain range
A mountain range is a single, large mass consisting of a succession of mountains or narrowly spaced mountain ridges, with or without peaks, closely related in position, direction, formation, and age; a component part of a mountain system or of a mountain chain...
is located in Enderby Land
Enderby Land
Enderby Land is a projecting land mass of Antarctica, extending from Shinnan Glacier at to William Scoresby Bay at .Enderby Land was discovered in February 1831 by John Biscoe in the whaling brig Tula, and named after the Enderby Brothers of London, owners of the Tula, who encouraged their...
, in the claimed Australian Antarctic Territory
Australian Antarctic Territory
The Australian Antarctic Territory is a part of Antarctica. It was claimed by the United Kingdom and placed under the authority of the Commonwealth of Australia in 1933. It is the largest territory of Antarctica claimed by any nation...
, East Antarctica
East Antarctica
East Antarctica, also called Greater Antarctica, constitutes the majority of the Antarctic continent, lying on the Indian Ocean side of the Transantarctic Mountains...
.
Location
A subsidiary of the Enderby Land Coast RangesEnderby Land Coast Ranges
The Enderby Land Coast Ranges are a mountain range centered at in Enderby Land, in the Australian Antarctic Territory, East Antarctica. These ranges are considered to be a subset of their parent ranges, the Wilkes Land Coast Ranges. The Wilkes Land Coast Ranges are, in turn, a subsidiary of their...
, the Napier Mountains are located roughly 4 degrees west of Cape Boothby
Cape Boothby
Cape Boothby in East Antarctica is a rounded cape along the east side of the coastal projection of Edward VIII Plateau. It is situated north of Kloa Point, just north of Edward VIII Bay. It was discovered on 28 February 1936 by DI personnel on the RSS William Scoresby, and named for the captain...
, Edward VIII Bay
Edward VIII Bay
Edward VIII Bay is a bay about 20 miles in extent, located between Edward VIII Plateau and the Øygarden Group of islands. The head of the bay is occupied by the Edward VIII Ice Shelf...
and Edward VIII Ice Shelf
Edward VIII Ice Shelf
Edward VIII Ice Shelf is an ice shelf occupying the head of Edward VIII Bay. The northern part of this feature was called Innviksletta by Norwegian cartographers, who mapped it from aerial photos taken by the Lars Christensen Expedition, 1936-37. The area was first visited in 1954 by an ANARE ...
, and 3.5 degrees east of Amundsen Bay
Amundsen Bay
Amundsen Bay, also known as Ice Bay, is a long embayment wide, close west of the Tula Mountains in Enderby Land, Antarctica. The bay was seen as a large pack-filled recession in the coastline by Sir Douglas Mawson on January 14, 1930...
. The Napier Mountains are centered about 64 km south of Cape Batterbee
Cape Batterbee
Cape Batterbee is a small, rocky point on the coast, the most northerly cape of Enderby Land. It is located 92 km north of Mount Elkins.-Discovery and naming:Cape Batterbee was discovered by BANZARE on 13 January 1930...
in Enderby Land, East Antarctica. It extends about 64 km in a NW-SE direction from Mount Codrington
Mount Codrington
Mount Codrington is a prominent mountain, high, standing south-southeast of Cape Close and east of Johnston Peak. Mount Codrington forms the northeastern end of the Napier Mountains....
, and also includes Mount Kjerringa
Mount Kjerringa
Mount Kjerringa is an isolated peak, 1,220 meters above sea level, situated roughly north of Aker Peaks, west of Magnet Bay, and 57 km northeast of Mount Elkins in Enderby Land, East Antarctica.-Discovery and naming:...
, and the Young Nunataks
Young Nunataks
Young Nunataks is a group of nunataks in the Napier Mountains standing 2 nautical miles south of Mount Elkins. Mapped by Norwegian cartographers from aerial photos taken by the Lars Christensen Expedition, 1936-37. Remapped from aerial photos taken by ANARE in 1956 and named for W.F...
.
The Enderby Land Coast Ranges are considered to be a subset of their parent ranges, the Wilkes Land Coast Ranges
Wilkes Land Coast Ranges
-Location:Wilkes Land Coast Ranges are centered at in the Wilkes Land area of the Australian Antarctic Territory, East Antarctica. These ranges are considered to be a subset of their parent ranges, the East Antarctica Ranges. The highest peaks in the Wilkes Land Coast Ranges are listed below:-...
. The Wilkes Land Coast Ranges are, in turn, a subsidiary of their parent ranges, the East Antarctica Ranges
East Antarctica Ranges
The East Antarctica Ranges are one of the three largest mountain ranges in Antarctica, the others are the Transantarctic Mountains and West Antarctica Ranges. The East Antarctica Ranges, located on the East Antarctic Ice Sheet, have 29 known peaks whose summits reach or exceed 2000 meters above sea...
.
Discovery
The Napier Mountains were discovered in January 1930 by the British Australian New Zealand Antarctic Research Expedition (BANZARE) under Sir Douglas Mawson. They were named by Mawson after the Hon. Sir John Mellis Napier, a Judge of the Supreme Court of South AustraliaSupreme Court of South Australia
The Supreme Court of South Australia is the superior court for the Australian State of South Australia. It has unlimited jurisdiction within the state in civil matters, and hears the most serious criminal matters. The Supreme Court is the highest South Australian court in the Australian court...
, 1924–42 and Chief Justice of South Australia, 1942-67. This mountain range was first visited by an ANARE party in 1960. Members of this party included Syd Kirkby and Terence James Elkins
Terence James Elkins
Terence James Elkins is an Australian-born American physicist. In 1960, he participated in an expedition from Mawson Station which conducted the first geological surveys of the Napier Mountains in Antarctica. The highest of this group of mountains, Mount Elkins, was subsequently named after him...
.
Geology & orogeny
The Napier Complex is among the most ancient terrestrial terraneTerrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...
s on Earth. Its evolution is characterized by high-grade metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
and several strong deformations. At least four distinct tectonothermal events occurred in the Archaean Eon
Eon
-Science:* Aeon, a very long time* Eon , a collective problem solving project* Eon Mountain, in Canada* A measure of time in the geologic time scale- Fiction :* Eon , by Greg Bear...
:
- 3.8 billion years ago: occurrence of initial felsicFelsicThe word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....
igneous activityVolcanismVolcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
over a long period of time - 3.0 billion years ago: emplacement of charnockiteCharnockiteCharnockite is applied to any orthopyroxene-bearing granite, composed mainly of quartz, perthite or antiperthite and orthopyroxene , as an end-member of the charnockite series.-Charnockite series:...
at Proclamation IslandProclamation IslandProclamation Island is a small rocky island 2.5 nautical miles west of Cape Batterbee and close east of Aagaard Islands. Discovered by the British Australian New Zealand Antarctic Research Expedition , led by Mawson, 1929–1931, and so named, following the reading of a proclamation on its summit on... - 2.8 billion years ago: occurrence of a very-high grade discrete tectonothermal event (a UHT metamorphic event)
- 2.5 billion years ago: occurrence of a subsequent, protracted high-grade tectonothermal event
Much of the East Antarctic craton
East Antarctic craton
The East Antarctic craton is an ancient craton that forms most of Antarctica. The East Antarctic craton was part of the Nena supercontinent 1.8 billion years ago.During the early Paleozoic Era East Antarctica joined the Gondwana supercontinent.- Breakup :...
was formed in the Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
period by a series of tectonothermal orogenic
Orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
events. Napier orogeny formed the cratonic nucleus approximately 4 billion years ago. Mount Elkins is a classic example of Napier orogeny. Napier orogeny is characterized by high-grade metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
and plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
. The orogenic events which resulted in the formation of the Napier Complex (including Mount Elkins) have been dated to the Archean
Archean
The Archean , also spelled Archeozoic or Archæozoic) is a geologic eon before the Paleoproterozoic Era of the Proterozoic Eon, before 2.5 Ga ago. Instead of being based on stratigraphy, this date is defined chronometrically...
Eon
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
. Radiometrically dated
Radiometric dating
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
to as old as 3.8 billion years, some of the zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
s collected from the orthogneisses
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
of Mount Sones
Mount Sones
Mount Sones is a mountain standing on the north side of Beaver Glacier, 2 nautical miles west of Mount Reed in the Tula Mountains. It was plotted from air photos taken by ANARE in 1956 and was named by the Antarctic Names Committee of Australia in 1962 for F...
are among the oldest rock specimens found on Earth. Billions of years of erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and tectonic deformation
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
have exposed the metamorphic rock
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
core of these ancient mountains.
The oldest crustal
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...
components found to date in the Napier Complex appear to be of igneous
Igneous rock
Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...
derivation. This rock appears to have been overprinted by an ultra-high temperature metamorphic event (UHT) that occurred near the Archean-Proterozoic boundary. Using a lutetium-hafnium
Hafnium
Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869. Hafnium was the penultimate stable...
(Lu-Hf) method to examine garnet
Garnet
The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...
, orthopyroxene
Pyroxene
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
, sapphirine
Sapphirine
Sapphirine is a rare mineral, a silicate of magnesium and aluminium with the chemical formula 86O20 . Named for its sapphire-like colour, sapphirine is primarily of interest to researchers and collectors: well-formed crystals are treasured and occasionally cut into gemstones...
, osumilite
Osumilite
Osumilite a very rare hydrate potassium-sodium-iron-magnesium-aluminium silicate mineral. Osumilite is part of the milarite group of cyclosilicates.-Characteristics:...
and rutile
Rutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...
from this UHT granulite
Granulite
Granulites are medium to coarse–grained metamorphic rocks that have experienced high temperature metamorphism, composed mainly of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure...
belt, Choi et al determined an isochron
Isochron
In the mathematical theory of dynamical systems, an isochron is a set of initial conditions for the system that all lead to the same long-term behaviour.-An introductory example:...
age of 2.4 billion years for this metamorphic event. Using SHRIMPU–Pb zircon dating methodology, Belyatsky et al determined the oldest tectonothermal event in the formation of the Napier Complex to have occurred approximately 2.8 billion years ago.
Preservation of the UHT mineral assemblage in the analyzed rock suggests rapid cooling, with closure likely to have occurred for the Lu-Hf system at post-peak UHT conditions near a closure temperature
Closure temperature
In radiometric dating, closure temperature or blocking temperature refers to the temperature of a system, such as a mineral, at the time given by its radiometric date. In physical terms, the closure temperature at which a system has cooled so that there is no longer any exchange of parent or...
of 800°C. UHT granulites appear to have evolved in a low Lu-Hf environment, probably formed when the rocks were first extracted from a mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
profoundly depleted in lithophile elements. The source materials for the magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
s that formed the Napier Complex were extremely depleted relative to the chondritic uniform reservoir (CHUR). These results also suggest significant depletion of the early Archean mantle, in agreement with the early igneous differentiation
Igneous differentiation
In geology, igneous differentiation is an umbrella term for the various processes by which magmas undergo bulk chemical change during the partial melting process, cooling, emplacement or eruption.-Primary melts:...
of the Earth that the latest core formation models require.