Why do the Caribbean Islands Arc?
If you look at the Caribbean islands from above you’ll see that they arc, and new research by geophysicists at the University of Southern California have found that over the past 50 million years the Caribbean islands have been pushed east by the steady movement of the Earth’s viscous mantle against the more stationary Southern American continent.
The result of this study which was published in the journal Nature Geoscience yesterday give us a better understanding of how continents resist the constant movement of the Earth’s plates, and what effect continental plates have on reshaping the surface of Earth.
“Studying the deep earth interior provides insights into how the Earth has evolved into its present form,” said Meghan Miller, assistant professor of earth sciences at the USC Dornsife College of Letters, Arts and Sciences, and lead author of the paper. “We’re interested in plate tectonics, and the southeastern Caribbean is interesting because it’s right near a complex plate boundary.”
Everything is Connected
To be able to study the motion of the South American continent and the Caribbean plate, researchers Miller and Thorsten Becker, associate professor of earth sciences at USC Dornsife, had to first model the entire planet. In fact, the pair created 176 models, models that required several weeks at the USC High Performance Computing Center to compute.
“If you can, you want to solve the whole system and then zoom in,” Becker said. “What’s cool about this paper is that we didn’t just run one or two models. We ran a lot, and it allowed us to explore different possibilities for how mantle flow might work.”
“Oceanic plates are relatively simple, but if we want to understand how the Earth works as a system — and how faults evolved and where the flow is going over millions of years — we also have to understand continental plates,” Becker added.
Miller and Becker reconstructed the movement of the planet’s mantle to a depth of just above 3,000 kilometres.
Their research tossed previous hypotheses of the seismic activity beneath the Caribbean Sea out the window and provided an important new insight into the unique tectonic interactions that are behind the Caribbean plate tearing away from South America.
In particular, Miller and Becker point to a part of the South American plate — known as a “cratonic keel” — that is roughly three times thicker than normal lithosphere and much stronger than typical mantle. The keel deflects and channels mantle flow, and provides an important snapshot of the strength of the continents compared to the rest of the Earth’s outer layers.
In the southeastern Caribbean the researchers that the interaction of the subducted plate beneath the Antilles island arc in combination with the stronger continental keel has created the El Pilar-San Sebastian Fault. Miller and Becker believe that similar interactions are the cause of the San Andreas Fault.
“We’re studying the Caribbean, but our models are run for the entire globe,” Miller said. “We can look at similar features in Japan, Southern California and the Mediterranean, anywhere we have instruments to record earthquakes.”