Scientists from Imperial College London and collaborators have uncovered one of the final pieces of the global plate tectonic puzzle.
The ‘shell’ of the Earth is broken into seven or eight major and many minor pieces, known as tectonic plates. As these plates move they can trigger strong earthquakes and violent volcanic eruptions, and the Caribbean is often rocked by such disastrous events.
"The Caribbean plate sits below Central America and the Caribbean Sea and is surrounded by three other plates, making it an especially dynamic region with a lot of seismic activity," says Professor Saskia Goes of Imperial’s Department of Earth Science and Engineering (ESE). "We reconstructed how this plate has moved through time, and compared our modelling to x-ray type images made using earthquake waves recorded by state-of-the-art instruments on the ocean floor."
This new approach opens up new opportunities to advance our understanding. Prof. Jenny Collier Imperial's Earth Science and Engineering Department
The experiment was conducted aboard the UK research ship RRS James Cook in collaboration with geophysicists at the Karlsruhe Institute of Technology’s (KIT) Geophysical Institute, Germany. The data collected enabled the team to probe 1,200 kilometres below the Earth’s surface to image plate fragments that have sunk beneath the present-day Caribbean Ocean. This plate material has moved and accumulated via subduction, a process whereby a heavier plate sinks beneath another, returning material deeper into the Earth.
“Using plate reconstruction, we could determine where and when these plate fragments sank into the interior of the Earth, and unravel the motions at the plate boundaries surrounding the Caribbean over the past 100 million years,” says Benedikt Braszus, a Master’s student in geophysics at the KIT and lead author of the paper.
The researchers found that material currently lying deep beneath South America corresponds to seafloor fragments of an ancient Caribbean arm of the Atlantic that subducted some 90 to 115 million years ago, before a notable spike in volcanism occurred in the region and formed a major ocean plateau. At shallower depths, plate material has built up over the past 70 million years as subduction formed the plate’s long arc of bordering volcanoes (visible to the right of the tectonic map below).
They find that the subducted Atlantic plate looks much more fragmented and twisted than plates found deep below the Pacific Ring of Fire. The Caribbean plate material contains a number of tears, gaps, and fractures along plate ridges, which can be traced back to different stages of subduction between the Caribbean and other plates throughout history.
"Traditionally, we use surface observations to determine the tectonic history of an area,” adds Professor Jenny Collier of ESE. “This new approach, through imaging pieces of former seafloor now hundreds of kilometres into the Earth, opens up new opportunities to advance our understanding."
The research was carried out as part of the internationally collaborative ‘VoiLA’ project (Volatile Recycling in the Lesser Antilles). This project, funded by the Natural Environment Research Council (NERC), is combining multidisciplinary measurements and models of the Lesser Antilles to understand subduction and its role in the deep Earth water cycle in the region.
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