Magnetic properties of volcanic rocks reveal an earlier collision between Central and South America

A new study published in Earth and Planetary Physics provides fresh insight into the timing of one of the most important tectonic events shaping the Americas: the collision between Central America and South America. By analyzing the magnetic properties of volcanic rocks from the Northern Andes of Colombia, researchers show that the main collisional stages occurred earlier than previously thought—before about 10 million years ago.

The study was led by Victor Piedrahita (first author) and J. Li (corresponding author), together with an international team of geoscientists. The researchers focused on late Miocene volcanic rocks (approximately 12–6 million years old) from the Combia Volcanic Province, located in central Colombia. These rocks formed during a critical interval when the South American Plate was interacting with the continental part of Central America.

To unravel this complex tectonic history, the team applied magnetic fabric analysis, a technique that examines how magnetic minerals within rocks are aligned. This method allows scientists to distinguish between original volcanic flow patterns and later deformation caused by tectonic stresses. “Volcanic rocks can preserve a remarkably detailed record of geological processes,” says Dr. Victor A. Piedrahita. “Their magnetic fabrics help us determine whether deformation occurred before, during, or after the rocks were emplaced.”

The results show that many of the volcanic rocks preserve primary magnetic fabrics related to magma or volcanic debris flow, indicating little or no tectonic overprinting during the late Miocene. Other sites record localized deformation, but these effects are limited in extent and intensity. Together, the findings suggest that major crustal shortening and collision-related deformation in the Northern Andes had largely ceased before the late Miocene.

“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,” explain Piedrahita and Li. “By the time these volcanic rocks formed, tectonic deformation had become weaker and more localized.”

These conclusions help refine models of Andean mountain building and improve our understanding of how plate interactions shaped the geological evolution of the Americas. The study also demonstrates the power of magnetic methods for reconstructing tectonic histories in volcanic regions. This research was supported by grants from the National Natural Science Foundation of China (NSFC), awarded to J. Li and Victor Piedrahita.