A keystone in a changing world - Antarctica: Global Science from a Frozen Continent - page 57

Figure 2.22 Basaltic dykes and sills in Marie Byrd Land
related to volcanic activity active when New Zealand
rifted from Antarctica (Credit: Bryan Storey)

Intriguingly, most of the Gondwana
breakup stages described above were
associated with intense periods of
volcanic activity. The opening of the
South Atlantic resulted in the
separation of South America from Africa. Two present day volcanic islands, Tristan
da Cunha and St Helena, are connected via submarine ridges to large volcanic
provinces, the Parana basaltic province in South America and the Etendeka province
in Africa, respectively. Although we know the volcanic provinces are in some way
related to continental breakup, the cause and effect are still matters of debate and
ongoing research.

A jigsaw puzzle: rotating microcontinents

Whatever processes controlled or in uenced the breakup of Gondwana, for the

most part the supercontinent separated into the major continents as we know
them today. However, some small microplates were also formed, particularly in the
South Atlantic region, and these help to explain some of the geographic features of
Antarctica, particularly the Ellsworth Mountains. An Ellsworth microplate, formed at
the time of breakup, rotated clockwise more than 90º and migrated from an original
position between South Africa and Antarctica to its present position at the head of the
Weddell Sea. This explains the anomalous direction of the Ellsworth Mountains,
relative to the Transantarctic Mountains. It also explains the anomalous position
of a small group of nunataks, Haag Nunataks, discovered in the 1980s to be old
metamorphic rocks from East Antarctica that formed approximately 1200million
years ago. They too represent an exotic block that now forms part of West Antarctica.
The Falkland Islands, like the Ellsworth Mountains, rotated 180º from a similar
position between Africa and Antarctica to join South America on the opposite
side of the Atlantic. We cannot be sure exactly how and why these microplates and
rotations occurred or why Gondwana should have broken up in this way, but many
suspect that it is in some way linked to the formation of the volcanic province at
the start of rifting. The trajectory, displacement history and rotation mechanisms
of the microplate component of the Gondwana jigsaw remain a mystery.
Interestingly, displaced microplates are also a signi final

separation of South America from the Antarctic Peninsula and the opening of Drake

cant component of the