Geologists Reveal the Americas Collided Earlier Than We Thought

A new geological study reshapes the timeline of a major tectonic collision that helped form the Andes, suggesting key events occurred earlier than long assumed.

A study in Earth and Planetary Physics is reshaping scientists’ understanding of how the Americas came together. By examining subtle magnetic signals locked inside ancient volcanic rocks in Colombia’s Northern Andes, researchers found that a major phase of the collision between Central and South America likely wrapped up earlier than long assumed, before about 10 million years ago. This shift in timing could change how scientists interpret the rise of the Andes and the evolution of landscapes across the region.

The work, led by Victor Piedrahita (first author) and J. Li (corresponding author), focuses on rocks from the Combia Volcanic Province in central Colombia.

These late Miocene formations (approximately 12–6 million years old) formed during a period when tectonic forces were still active, making them valuable records of what was happening deep within Earth’s crust. Because volcanic rocks cool and solidify relatively quickly, they can preserve a snapshot of conditions at the time they formed, almost like a geological timestamp.

Magnetic Clues From Volcanic Rocks

To better understand this tectonic history, the researchers used magnetic fabric analysis, which examines how magnetic minerals within rocks are oriented. This approach helps scientists separate original volcanic flow patterns from deformation that occurred later due to tectonic forces.

“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.”

Evidence for Earlier Collision

The analysis revealed that many of the rocks still retain their original magnetic fabric, linked to magma movement or volcanic debris flows. This suggests that they experienced little to no tectonic alteration during the late Miocene. Some locations do show signs of deformation, but these are limited in scale and intensity.

Overall, the findings indicate that major crustal shortening and deformation tied to the continental collision had mostly ended 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.”

Implications for Andean Evolution

These results refine current models of how the Andes formed and provide a clearer picture of how interactions between tectonic plates shaped the region. The study also highlights the usefulness of magnetic techniques for reconstructing tectonic histories in volcanic environments.

Reference: “Magnetic fabric of the late Miocene extrusive rocks of the Combia Volcanic Province: Tectonic implications for the northern Andes ” by Victor A. Piedrahita, Martin Chadima, Jackeline Ramírez, Alejandra Tabares, Maria I. Marín-Cerón and JinHua Li, 29 September 2025, Earth and Planetary Physics.
DOI: 10.26464/epp2026011

This research was supported by grants from the National Natural Science Foundation of China (NSFC), awarded to J. Li and Victor Piedrahita.

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