October 10, 2013
New Subduction Zone Process Identified In Atlantic Ocean
Lee Rannals for redOrbit.com - Your Universe Online
Over a period of 300 million to 500 million years, supercontinents have formed and ocean basins have opened and closed. The latest high-resolution surveys of the seafloor is the first direct evidence of the in-between phase.
“Every first-year geology student learns about the Wilson Cycle: Oceans open and then new subduction zones form and the oceans close,” Robert Stern, a geoscientist at the University of Texas at Dallas, told Earth Magazine. “But we don’t actually see evidence."
Scientists now believe they have evidence of this process starting in the Atlantic Ocean, off the coast of Portugal. According to their estimates, this nascent subduction zone could close the Atlantic Ocean in roughly 200 million years.
The researchers created a new map of the region and identified the main tectonic driving mechanisms, which included the westward movement of the Gibraltar Arc and the convergence of the African and Eurasian plates. These tectonic movements could be forcing the plates downward to form a new subduction zone.
“This area is very complex and there have always been a lot of competing and apparently contradictory models,” João Duarte, a geophysicist at Monash University in Melbourne, Australia, told EARTH Magazine. “Our model unifies previously contradictory models of this region in a consistent framework that accounts for all of the present structures.”
He said it is still too early in the evolution of the new subduction zone for all the typical subduction features to have formed. Instead, what the scientists see is a set of thrust faults that extend for 186 miles along the margin, which is what they expect to see before a subduction zone initiates.
If the convergence continues the margin may take another 10 million to 20 million years to develop into a mature subduction zone.
“The Atlantic Ocean is about 200 million years old,” Duarte told EARTH Magazine. “If the process is reversed [and the ocean basin closes], it’s likely that it will take another 200 million years to close.”
Stern, who was not involved in the study, is doubtful of Duarte's findings, saying he doesn't believe thrust faults alone are sufficient enough evidence to declare the southwest Iberian margin a nascent subduction zone. He says that it is just too early to tell, and there is no deep seismicity or volcanic arc yet.