Friday, July 29, 2011

Pangaea: Wandering Poles and Continents Debate


The supercontinent Pangaea, which roughly 300-200 million years ago existed as the only landmass on Earth, plays a special role in the history of geophysics. 

Animation of the break-up of Pangaea and the formation of modern continents.
File:Pangea animation 03.gif
Image: Wikipedia

The geological, biological, and paleontological similarities between now-distant shores -- once connected in Pangea -- gave the first evidence for the theory of continental drift. That Pangea came apart to form the modern world is well established, but exactly how, when, and where the individual plates moved are still up for debate.
Pangaea, from Ancient Greek πᾶν pan "entire", and Γαῖα Gaia "Earth", Latinized as Gæa) was the supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration.

The name was coined during a 1926 symposium discussing Alfred Wegener's theory of continental drift. In his book The Origin of Continents and Oceans (Die Entstehung der Kontinente und Ozeane) first published in 1915, he postulated that all the continents had at one time formed a single supercontinent which he called the
File:Pangaea continents.svg
Image: Wikipedia

"Urkontinent", before later breaking up and drifting to their present locations.

The single enormous ocean which surrounded Pangaea was accordingly named Panthalassa.

Drawing on new high-quality paleomagnetic data, Domeier et al. describe the movements of Gondwana that, until its separation from Laurasia 200 million years ago, formed the southern half of Pangea. The authors collected samples drawn from the Sierra Chica, a band of ancient volcanic rocks in central Argentina. Within the samples the magnetic minerals hematite and titanomagnetite were used to calculate the geographic location of the magnetic pole 263 million years ago. 

 Gondwana and Laurasia
File:Laurasia-Gondwana.svg
Image: Wikipedia

Because the Earth's magnetic poles drift only slightly over time and have well-known reversal episodes, deviations in the location of the calculated pole (paleopole) from the present location are an indication that the plate underlying the volcanic rock has moved since the lava solidified. Changes in the paleopole drawn from samples of different ages from the same plate give a map for the plate's movement.
A global paleogeographic reconstruction of the Earth during the Late Triassic, approximately 220 Mya, showing Gondwana breaking away from Laurasia in the north
File:LateTriassicGlobal.jpg
Image: Wikipedia

Previous research had trouble reconciling the paths traveled by Gondwana and Laurasia, despite the fact that the two landmasses were still joined at the time. The authors' paleopole, whose location and age were determined more accurately than in most related research, falls in between those previously calculated from Gondwanan and Laurasian samples. 

They suggest that any apparent differences between the paleopoles for Gondwana and Laurasia are due to sampling bias and other sources of error.


Citation: Geochemistry, Geophysics, Geosystems, doi:10.1029/2011GC003616, 2011 http://dx.doi.org/10.1029/2011GC003616

Title: New Late Permian paleomagnetic data from Argentina: Refinement of the apparent polar wander path of Gondwana

Authors: Mathew Domeier: Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, USA;

Rob Van der Voo; Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, United States and Center for Advanced Study, Norwegian Academy of Science and Letters, Oslo, Norway;

Eric Tohver: School of Earth and Geographical Sciences, University of Western Australia, Crawley, Western Australia, Australia;

Renata N. Tomezzoli and Haroldo Vizan: Departamento de Ciencias Geológicas, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, Argentina;

Trond H. Torsvik: Center for Advanced Study, Norwegian Academy of Science and Letters, Oslo, Norway; and Department of Physics, University of Oslo, Oslo, Norway; and School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa;

Jordan Kirshner: Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, United States.

1 comment: