Plate Nº 83 · recorded October 10, 2026
Earth & ClimateReported finding
Colombia's Ancient Volcanic Rocks Rewrite the Andes' Timeline
Magnetic analysis of 12-to-6-million-year-old lavas from Colombia suggests the main tectonic crunch between Central and South America ended earlier than geologists had believed, well before the late Miocene.
By Elena Vasquez3 min read555 words
In brief
- Published September 9, 2026 in Earth and Planetary Physics (Vol. 10, No. 1), DOI: 10.26464/epp2026011
- Analyzed volcanic rocks aged 12 to 6 million years old from the Combia Volcanic Province in central Colombia
- Main collision events placed in the Oligocene to middle Miocene, roughly 34 to 12 million years ago — earlier than previous estimates
- Used magnetic fabric analysis, a technique that reads the alignment of magnetic minerals inside rocks
- Funded by the National Natural Science Foundation of China through grants to JinHua Li and Victor Piedrahita
Colombia's 12-to-6-million-year-old volcanic rocks are pointing to a major rewrite of how the Americas came together. New magnetic analysis suggests the main collision between Central and South America peaked in the Oligocene–middle Miocene — roughly 34 to 12 million years ago — and had largely wound down well before the late Miocene.
The study, published September 9, 2026 in Earth and Planetary Physics, examined lavas from the Combia Volcanic Province in central Colombia. Victor A. Piedrahita led the work as first author, with JinHua Li (J. Li) as corresponding author. Co-authors include Martin Chadima, Jackeline Ramírez, Alejandra Tabares, and María I. Marín-Cerón.
What did the researchers actually measure?
The team used magnetic fabric analysis. The technique reads the alignment of magnetic minerals locked inside a rock. That alignment preserves a record of what physically shaped the rock — original magma flow, a tumbling debris cascade, or later squeezing by tectonic forces.
"Volcanic rocks can preserve a remarkably detailed record of geological processes," Dr. Piedrahita said. "Their magnetic fabrics help us determine whether deformation occurred before, during, or after the rocks were emplaced."
If a rock was heavily squeezed long after it solidified, its magnetic grains rotate and line up with the direction of tectonic stress. If the magnetic fabrics still match the original flow direction, the rock escaped major later deformation.
What did the Colombian rocks show?
Most Combia samples still carry their original, flow-related magnetic fabrics. That pattern suggests tectonic forces did not significantly reshape the rocks after they formed.
A handful of sites did record deformation, but the team describes those signals as limited in both strength and geographic spread.
Together, the evidence places the strongest crustal shortening in the Northern Andes before the late Miocene — earlier than many prior estimates.
How much earlier than thought?
The researchers place the main collisional events in the Oligocene to middle Miocene — roughly 34 to 12 million years ago.
"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 wrote. "By the time these volcanic rocks formed, tectonic deformation had become weaker and more localized."
By about 10 million years ago, the rocks show, the Andes-building engine had shifted into a lower gear.
Why does this matter for science?
The shift could refine computer models of Andean uplift and clarify how two tectonic blocks meeting shaped South America's geology. The work also demonstrates the wider utility of magnetic techniques in volcanic regions, where surface geology alone often hides deformation history.
Magnetic fabric analysis is non-destructive and works on small samples — useful in remote or weathered outcrops.
Limitations and open questions
The study covers a single region: the Northern Andes of Colombia. Whether the same early-decline pattern holds along the full length of the mountain belt, or elsewhere in Central and South America, remains untested.
Magnetic fabric analysis can also miss signals if a rock has been reheated, chemically altered, or heavily weathered — all common in tropical settings. The authors flag that some deformation-bearing samples may have started from mixed primary fabrics, complicating straightforward interpretation.
The research was funded by the National Natural Science Foundation of China through grants awarded to JinHua Li and Victor Piedrahita.
via dx.doi.org (Original)
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