Oz scientists describe Yo-Yo earth movement

Melbourne: A new phenomenon described as "yo-yo subduction" could help scientists better model the geological processes that lead to mountain building, volcanoes and earthquakes, Australian researchers have claimed.

"The place where earthquakes are generated has a more complex and chaotic behaviour than previously thought," said Dr Daniela Rubatto, a Geologist with the Australian National University.

Subduction happens when two tectonic plates are pushed together and one of the plates goes under the other. Most of the material that is pushed down is never seen again, but a small amount of it is pushed back up and helps form mountain belts.

The current wisdom is that there is a single `conveyor belt` movement of the Earth`s crust down and then one coming back up.

According to ABC, Rubatto said, her research suggests that the processes at subduction zones is more complex than this Rubatto and team have found that even as one plate is pushed down, pieces of crust break off at a depth of 20 to 100 kilometres, come up, and are then pushed back down again.

"This simple movement of a plate going down is much more complicated and has an internal chaotic movement,"she said adding "This is yo-yo subduction".

The evidence for yo-yo subduction came from the Italian Western Alps that are now 2000 metres above sea level.

Rubatto and his team used an ion probe known as the ANU SHRIMP to analyse the age and chemical composition of minerals in rock called eclogite, which originally formed 80 kilometres below the surface.

"The composition of these minerals change with depth so if I know the composition of the minerals, I know the depth," she said. Using this relationship, the researchers worked out the depth of the minerals at different periods dating back 65 to 80 million years ago.

They found that during this period, the rocks moved at a rate of centimetres a year, down 100 kilometres, back up and back down again."The rate of movement is more or less at the rate of the growth of your fingernail," she added.

She said the research will help refine scientific models of subduction "Any model of subduction will eventually feed into understanding earthquake evolution and dynamics and prediction, to some extent," she added.