Antarctic geology

The Vestfold Hills in East Antarctica. Only about one percent of Antarctica’s rock base is visible where it pokes through the ice sheet in the form of coastal outcrops, mountain ranges or isolated peaks called nunataks.

Like all other continents, Antarctica has at its core an ancient shield. The rocks of the East Antarctica shield are as old as 4 billion years, which means that they are amongst the oldest known rocks on Earth.

The age of the Earth is estimated to be 4.6 billion years and thus, ancient Antarctic rocks can be studied to gain insight into processes active in the early days of the Earth’s history. These most ancient rocks are very well-exposed in Enderby Land at the western extremity of the Australian Antarctic Territory.

Many other rock groups formed as sequences of volcanic rocks and sediments at 2.5 to 2.8 billion years ago, and others at 1.4 billion years.

The ancient shield is not homogeneous but can be subdivided into clearly separable units (cratons). These cratons and the boundaries between them have been the locations of much activity as the cratons have moved against one another. In other continents, the same structure and similar age relationships are known. Most of the world’s mineral resources come from these cratonic units and thus it is reasonable to expect that the Antarctic shield has the same mineral resource potential as other parts of the globe. However there are some features of Antarctica that dramatically reduce the chance of mineral availability (see Mining).

In many ways, the evolution of Antarctica appears to be similar to that of Australia. The fossil record of the two continents is similar, and Antarctica has yielded dinosaurs, amphibians and even marsupials from ages when the continents were part of the same land mass — a supercontinent called Gondwana (see Antarctic Prehistory).

Eighty five million years ago Australia began to separate from Antarctica. The separation started slowly at first at a rate of only a few millimetres a year. This accelerated to the present rate of 7cm a year. Australia completely separated from Antarctica about 30 million years ago.

Antarctica without its ice

People who consider Antarctica to be a small continent will be surprised to discover that it is larger than Europe and nearly twice the size of Australia. The Antarctic continent, excluding its ice shelves, covers over 13 million square kilometres compared with 7.7 million km² for Australia, or 10.5 million km² for Europe. The map below gives some idea of relative size.

Ninety-nine percent of Antarctica has a permanent blanket of snow and ice. Only about one percent of the continent’s rock base is visible where it pokes through the ice sheet in the form of coastal outcrops, mountain ranges or ‘nunataks’ which are isolated peaks.

The Transantarctic Mountains divide the continent into two contrasting parts, the East and West. The Transantarctic Mountains constitute one of the world’s longest and most impressive mountain chains. They extend from the north western corner of the Ross Sea to the south western corner of the Weddell Sea. West Antarctica, which includes the Antarctic Peninsula, is smaller and has a complex geological history. West Antarctica consists of four land units each with a different history. There has been major volcanic activity here in recent geological times and there are still a few active volcanic centres. Deep waters exist between land units and the West Antarctic ice sheet, which can be considered to a be floating ice mass, held in place by land peaks. West Antarctica includes the Vinson Massif, which has the highest peak in Antarctica at 5140 metres.

Most of East Antarctica is still not well known by geologists but it does include the Transantarctic Mountains. These commonly exceed 4000 metres elevation. The shield is very depressed in the centre, where it carries the bulk of the Antarctic ice sheet. Large areas lie deeper than 1000 metres below sea level.