A team of researchers at the Stanford Doerr School of Sustainability has used the isotopic make-up of minerals to measure historic altitudes in sedimentary rocks to show that one of the world’s most familiar mountain ranges, the Himalayas, did not form as experts have long assumed.
“The controversy rests mainly in what existed ‘before’ the Himalayas were there,” explains Page Chamberlain, professor of Earth and planetary sciences and of Earth system science at the Doerr School of Sustainability, and senior author of the study. “Our study shows for the first time that the edges of the two tectonic plates were already quite high prior to the collision that created the Himalayas—about 3.5 kilometers on average.”
In the classic model, the Himalaya mountain range formed when the Indian subcontinent collided northward with Eurasia about 65 million years ago, pushing oceanic crust and continental fragments upwards.
“Experts have long thought that it takes a massive tectonic collision, on the order of continent-to-continent scale, to produce the sort of uplift required to produce Himalaya-scale elevations,” explains Daniel Ibarra, Ph.D., a postdoctoral researcher from Chamberlain’s lab, first author of the paper, and now an assistant professor at Brown University. “This study disproves that and sends the field in some interesting new directions.”
The researchers looked at oxygen isotopes preserved in minerals to determine the altitude at which they formed, reconstructing the topography of the Himalayas before the continent collision.
Almost all minerals contain traces of oxygen in their crystalline structure, as does H2O or water. Oxygen exists in three stable isotopes: oxygen 16, 17, 18. Oxygen isotopes behave chemically in an identical manner, but due to the slight mass difference, water molecules containing heavy oxygen isotopes tend to evaporate and precipitate at different rates. A mineral formed at a lower altitude near the ocean will show a higher level of lighter isotopes and vice versa.
Sampling quartz (SiO2) veins from lower altitudes in southern Tibet and using oxygen analysis, the team showed that the foundations of the Gangdese Arc – a major geological unit at the base of the Himalaya mountains – were already much higher than anticipated, long before any tectonic collision occurred.
“This new understanding could reshape theories about past climate and biodiversity,” Ibarra concludes. The formation of the Himalayan mountains as an effective barrier for rain and atmospheric currents has long been seen as an important factor shaping weather patterns over Asia and the Indian Ocean. But the new paleo-topographic reconstruction, with high-elevation terain predating their formation, will likely lead to new paleoclimatic assumptions. It could also beget closer scrutiny of other key mountain ranges, such as the Andes and the Sierra Nevada, formed in a similar manner by the collision of Earth’s tectonic plates.
The study “High-elevation Tibetan Plateau before India–Eurasia collision recorded by triple oxygen isotopes” was published in the journal Nature Geoscience (2023). Additional material provided by Stanford University.
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