A new study suggests that a Colombian mountain range has lost its “root” – a wedge of crust that once supported it, but has since “dripped” into the mantle. It has long been a mystery how the peaks manage to stay upright, but now, researchers are investigating the underlying geology.
The Sierra Nevada de Santa Marta, a mountainous region in northwestern Colombia with peaks more than 18,700 feet (5,700 meters) high, has puzzled geologists since the 1970s, when measurements indicated that the crust beneath the peaks was unusually thin.
“Mountain areas usually have thick crustal roots that compensate for the load of the mountains,” says the study’s lead author. David QuirogaThe data scientist and former graduate researcher in geophysics at the University of Alberta in Canada told Live Science in an email. The Earth’s crust is much lighter than the Earth’s crust Latent mantle“, said Quiroga. Because the mountains are so heavy, the crustal roots that lie beneath them are embedded in the mantle. The mass displaced within the mantle is greater than the mass of the crustal root, and this formation compensates for the load accumulated on the mountains that lie above them.
Geologists can determine the thickness of the Earth’s crust using measurements of gravity anomalies. “In general, there is high gravity in places where there is a lot of mass, and vice versa,” Quiroga said. The presence of a crustal root in mountainous regions usually results in negative gravity anomaly values, meaning that the mass in this region is lower than expected. This reflects where light crust has replaced heavy mantle, as opposed to other places where the mantle is intact.
“However, in the case of the Sierra Nevada de Santa Marta, in Colombia, there is a high mountainous region with a high positive gravity anomaly,” Quiroga said. “This means that instead of there being a mass deficit, there is a mass surplus.”
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The mountain range once had a crustal root to compensate for its massive load, but that root slowly seeped into the mantle over 10 million years, according to the study published Jan. 7 in the journal Nature. Journal of Geophysical Research: Solid Earth.
The Earth’s crust and upper mantle form a solid crust around our planet known as the lithosphere. Quiroga said the lower layer of lithosphere may be “falling off” in places where it is heavier and cooler than the mantle below. The mantle then rises to fill the gaps and heats the lower crust, which can lead to changes in its composition that cause larger portions of the crust to sink.
former research It has been suggested that lithospheric dripping may explain positive gravity anomalies in other regions – Including the Puna Plateau in the AndesThe Sierra Nevada in California and the Wallowa Mountains in Oregon. But he said Quiroga and his colleagues were “the first to suggest that such a mechanism is a plausible explanation for the Sierra Nevada de Santa Marta.”
It’s unclear how the Colombian mountain range manages to stay upright despite its apparent lack of support, but the devil may be in the details.
“The models in our study show that once a mountainous area loses its crustal roots, it begins to sink due to loss of support,” Quiroga said. “Because the mountain is still upright and tall, this suggests that the removal occurred very recently, and that there has not been enough time for the mountain to collapse.”
Quiroga said the peaks may have lost their roots two million years ago. In the study, the researchers also suggest that a possible window for distillation occurred between 56 million and 40 million years ago, during the Eocene epoch. This later time frame suggests that the mountains remained upright for more than 40 million years, which contradicts the models in the study. A study predicted collapse after only 5 million years
But there are other factors not included in the models that may have supported the mountains over the ages. Quiroga said the surrounding lithosphere may have been strong enough to provide support to the peaks on both sides, and the mantle may have lifted to delay the mountains from collapsing. He added that the Caribbean tectonic plate, which is sliding under Colombia, should also be considered as a potential buttress in future models.
Until then, the mystery surrounding the Sierra Nevada de Santa Marta remains.