Study: Central and South America Collided Millions of Years Earlier Than Thought

A new study is changing scientists' understanding of when Central America and South America underwent one of the major tectonic collisions that helped shape the Americas. Examining the magnetic characteristics of volcanic rocks in Colombia's Northern Andes, researchers found evidence that the main phases of the collision took place earlier than previously believed — before about 10 million years ago.

The research, published in Earth and Planetary Physics, was led by Victor Piedrahita and J. Li, along with an international group of geoscientists. The team studied late Miocene volcanic rocks, roughly 12 to 6 million years old, from the Combia Volcanic Province in central Colombia, which formed during a period when the South American Plate was interacting with the continental portion of Central America.

To reconstruct the tectonic activity, the researchers used magnetic fabric analysis, which studies the orientation of magnetic minerals inside rocks to reveal whether their internal structure reflects original volcanic processes or later deformation. "Volcanic rocks can preserve a remarkably detailed record of geological processes," said Dr. Victor A. Piedrahita. "Their magnetic fabrics help us determine whether deformation occurred before, during, or after the rocks were emplaced."

The team found that many of the volcanic rocks still retained primary magnetic fabrics created by magma movement or volcanic debris flows, suggesting they experienced little or no major tectonic deformation during the late Miocene. Some locations did show signs of deformation, but these effects were limited in both strength and geographic extent, indicating that the strongest crustal shortening in the Northern Andes had mostly ended before that time.

"Our data indicate that the most significant collisional events between Central and South America occurred earlier than we previously thought, mainly during the Oligocene-middle Miocene," Piedrahita and Li said. "By the time these volcanic rocks formed, tectonic deformation had become weaker and more localized."