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Sediment Accelerates Plates

A new study by The University of Texas at Austin has demonstrated a possible link between life on Earth and the movement of continents. The findings show that sediment, which is often composed from pieces of dead organisms, could play a key role in determining the speed of continental drift. In addition to challenging existing ideas about how plates interact, the findings are important because they describe potential feedback mechanisms between tectonic movement, climate and life on Earth.

The study, published Nov. 15, 2018,in Earth and Planetary Science Letters, describes how sediment subducting beneath tectonic plates could regulate the movement of the plates and may even play a role in the rapid rise of mountainvranges and growth of continental crust.

The research was led by Whitney Behr, a research fellow at the Jackson School and professor at ETH Zurich in Switzerland, and co-authored by Thorsten Becker, a professor and Shell Chair in Geophysics in the Department of Geological Sciences and the Institute for Geophysics (UTIG).

Sediment entering subduction zones has long been known to influence geological activity such as the frequency of earthquakes, but until now, it was thought to have little influence on continental movement. That’s because the speed of subduction was thought to be dependent on the strength of the subducting plate as it bends and slides into the viscous mantle. However, prior research involving UTIG scientists had shown the subducting plates may be weaker and more sensitive to other influences than previously thought.

Subsequent modelling showed that rock made of sediment can create a lubricating effect between plates, accelerating subduction and plate velocity.

This mechanism could set in motion a complex feedback loop. As plate velocity increases, sediment would have less time to accumulate. This would lead to slower subduction, which might allow for mountains to grow at plate boundaries as the force of the two plates running into each other causes uplift. In turn, erosion of those mountains by wind, water and other forces would produce more sediments, which could restart the cycle by increasing the speed of subduction.

Behr and Becker’s new model also offers a compelling explanation for variations found in plate speed, such as India’s dramatic northward acceleration some 70 million years ago. The authors propose that as India moved through equatorial seas teeming with life, an abundance of sedimentary rock formed by organic matter settling on the seafloor created a lubricating effect. India’s march north accelerated from 5 centimeters per year (about 2 inches) to 16 centimeters per year (about 6 inches). As the continent accelerated, the amount of sediment being subducted decreased, and India slowed before finally colliding with Asia.