In June 2016 the Humboldt Awardee Trond Torsvik came to the GFZ where he is working together with the team of Bernhard Steinberger of the GFZ section Geodynamic Modelling. Torsvik is one of the internationally leading scientists in the field of plate tectonic reconstructions. In 2013 he founded the Centre for Earth Evolution and Dynamics at the University of Oslo, Norway. Until July he will stay at the GFZ where he tries to improve methods and models in his field of research, together with the GFZ scientists.

GFZ: What is it that fascinates you about the research field of plate tectonics, the changes in the positions of oceanic and continental plates, of the geologic past?

Trond Torsvik: For several decades I have been passionate about understanding the restless movements of the continents, making maps of the distribution of tectonic plates and to show where the lands and seas were situated in the geological past.

The Earth is unique because plate tectonics have not been identified on any other terrestrial planets, but when and how plate tectonics started is still debated - perhaps about three billion years ago.

GFZ: For the reconstruction of the location of tectonic plates you use paleomagnetic data. What do these data tell you and how does it help you to reconstruct the position of the plates?

Torsvik: The inclination, so to speak the dip of the Earth’s magnetic field varies systematically with latitude. This is of prime importance for paleomagnetic reconstructions. Paleomagnetism is the study of the Earth’s magnetic field preserved in rocks. By measuring the magnetic inclination in old rocks in the laboratory we can determine at what latitude the rock and the continent formed.

By collecting rocks from all over the planet from various geological times we can build paleo-geographic maps: Ancient longitude however cannot be determined from palaeomagnetism but we have developed some analytical methods that can constrain longitude semi-quantitatively.

GFZ: Only since the beginning of the 20th Century it is known that the tectonic plates are in motion. Today, how much do we actually know about plate tectonics?

Torsvik: The German scientist Alfred Wegener was the first to propose that all the continents once formed a single supercontinent surrounded by a vast marine area. There are many similarities between his hand-drawn Pangea reconstruction - originally named “Urkontinent” - and our modern computer-aided reconstructions of Pangea. But an important difference is that we are now able to position Pangea in its ancient latitude and longitude.

Subduction of plates into the Earth’s mantle also only became clear in the early 1960’s. Adding subducted material in the mantle we consider a prime cause for changing the orientation of the Earths spin axis: the true polar wander. But Earth rotation perturbations due to ice-age loading is also a well-known phenomenon: The present rate of true polar wander – about ten centimetre per year - is largely described by viscoelastic response to the Pleistocene deglaciation and demonstrates that climate change is also a trigger of this phenomenon.

Today we know a lot about the link between plate tectonics and processes in the Earth’s underlying mantle, which conceptually can be viewed as a simple mass-balance: subducted plates restore mass to the mantle and trigger the return flow toward the surface.

GFZ: Did you already come to new findings during your time at the GFZ?

Torsvik: My time at GFZ has been incredibly busy, I finalized a book on “Earth History and Palaeogeography”, and together with GFZ scientists we have explored, and hopefully explained the geometry of the Hawaiian-Emperor volcano chain: one of the most spectacular geological features on Earth.

The interview was led by Ariane Kujau

27.01.2017