What kind of rocks make up Antarctica? What geological processes are occurring today? What rock and mineral resources exist there?
The geology of Antarctica
Antarctica’s geology is highly varied. This is unsurprising considering the size of the continent and the changing tectonic processes, environments, and climates that it has experienced over geological time. However, because over 99% of the continent is covered in ice, Antarctica’s geology is not known in detail, and our understanding of the rocks and geological structures beneath the ice must be inferred from the limited area of rock (roughly 0.4% of the continent) that is exposed at the surface as well as from remote sensing technologies. These include satellite imagery, ground penetrating radar, the use of seismic waves, and the study of gravity anomalies. While many maps of Antarctica’s geology have been drawn at various scales, there is currently an effort to increase the detail of coverage and to make geological maps available digitally.
Study of Antarctica’s geology has led to many important insights: some rocks preserve evidence of times that were warmer as well as providing clues for scientists to reconstruct when and how the supercontinent Gondwana broke apart (as described in the previous section). While there has been a great deal of volcanic activity in Antarctica’s past, there are still some areas of volcanism in the continent today.
Antarctica is not without rock and mineral resources, however, for physical and political reasons (see below) these are not exploited at the present time.
Intriguingly, Antarctica is the best place in the world for finding meteorites. So not only is the continent an important place to study Earth’s geological history – it is also a window to the geology of the solar system.
The differences of East and West Antarctica
(million year = myr)
East and West Antarctica are quite distinct from each other in terms of their geology. East Antarctica is much larger and is an area of continental shield (or ‘craton’) composed of ancient igneous and metamorphic rocks, some exceeding 3 billion years in age. Overlying the ancient continental shield rock in various places are younger sedimentary rocks (e.g. sandstones, limestones, shales, and coal) which formed at different times under different environmental conditions. For example, coal beds exposed in the Transantarctic Mountains formed through the accumulation of plant matter during the Permian Period (290 to 245 myr ago) when the continent had a warm temperate climate. Over millions of years this organic material was buried; and by compaction under the weight of overlying sediment, it was eventually turned into coal.
Around the margins of the East Antarctic continental shield there are areas of basalt rock which formed through the solidification of basaltic lava during the break up of Gondwana. As the southern continents separated, volcanic activity associated with rifting caused extensive flood basalts: great quantities of lava emerged from fissure eruptions at various times and spread over the land to form successive layers of basalt rock. (Where magma was unable to reach the surface, igneous intrusions occurred to create sills and dykes within pre-existing rock formations.) By study of these areas of basalt, geologists have been able to identify the most active areas of rifting in the past as well as to work out the timing of separation between the different continental areas. For example, basalt from Antarctica that is identical to basalt from South Africa indicates a shared ‘volcanic province’. Radiometric dating of these volcanic rocks shows that they began forming around 180 myr ago indicating that these two continents began to break away from each other during the Jurassic Period.
The geology of West Antarctica has much in common with the geology of the Andes. In fact, this side of Antarctica owes its origin to the same mountain building processes that uplifted the western side of South America. During the early Jurassic (around 200 myr ago) oceanic crust began to subduct beneath the Pacific margin of Gondwana. The resulting subduction zone extended along the margin of what is now South America and West Antarctica. Volcanism above the subduction zone created new land adjoining the Gondwana margin that eventually became the Antarctic Peninsula (a continental margin arc). Subduction, volcanism, and uplift of this region occurred almost continuously until about 35 myr ago and ceased when the Antarctic Peninsula and South America finally separated to create the Southern Ocean.
Unlike East Antarctica, West Antarctica is made up of a number of relatively small plate fragments that have been merged together along the south-eastern Pacific compressional plate boundary. As compression took place, pre-existing rocks were folded, faulted and uplifted – spectacularly so in some places as seen in the Ellsworth Mountains which contain Antarctica’s highest peak (Mount Vinson).
The Transantarctic Mountains however, owe their origin to rifting rather than crustal compression and collision. From the Late Cretaceous Period onwards, there has been uplift and rifting between West and East Antarctica along what is known as the West Antarctic Rift. In places, this rift system is still active today and is the cause of present-day volcanic activity in Antarctica. The continent’s most active volcano, Mount Erebus, is located along this rift system, on Ross Island at the edge of the Ross Sea. It is one of the few volcanoes in the world to have an open, convecting lava lake within the crater at its summit. There are also several inactive volcanoes in the Transantarctic Mountains.
Read more about Antarctica’s volcanoes: