Himalayas had a leg up before reaching the skies

A new technique for measuring past topography.

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There’s no doubt that mountain ranges play a crucial role in changing the climate and shaping the flora and fauna. Knowing how Mountain ranges form is of great interest to those who research and model past climates.

Researchers at the Stanford Doerr School of Sustainability have demonstrated that the Himalayas did not form as experts have long believed. Using a method to analyze meteorites to determine historical elevations in sedimentary rocks, the new study shows for the first time that the edges of the two tectonic plates were already around 3.5 kilometers high before the collision that gave rise to the Himalayas.

Page Chamberlain, professor of Earth and planetary sciences and Earth system science at the Doerr School of Sustainability and senior author of the study, said, “The controversy rests mainly in what existed before the Himalayas were there.”

According to the findings, historical climate models must be recalculated, and new paleoclimatic assumptions may be made regarding the Himalayan region of Southern Tibet, known as the Gangdese Arc. The fact that this is more than 60% of their current height may cause assumptions about the past temperature and biodiversity to change.

It could lead to a closer look at other significant mountain ranges, such as the Andes and the Sierra Nevada. It is suspected that this uplift was caused by crustal shortening caused by the low-angle subduction of the Neo-Tethyan oceanic lithosphere. It is not easy to find proxies for the altitude in the geologic record, but Stanford researchers discovered an altitude proxy in collaboration with study authors from the China University of Geosciences (Beijing)

In addition to precipitation falling more heavily on windward slopes, the chemical composition of the precipitation changes as the air rises toward the peaks. There is a tendency for heavier isotopes to drop out first, while lighter isotopes tend to drop out near the peaks. This way, experts can determine the altitude at which the rocks were deposited by analyzing their isotopic composition.

Researchers from Stanford University found the Gangdese Arc’s foundations were higher than expected long before the tectonic collision by sampling quartz veins from lower altitudes in southern Tibet. There are three stable isotopes of oxygen in the sedimentary record: oxygen 16, 17, and 18. The key isotope, oxygen 17, is extremely rare. Only 0.04% of the oxygen on Earth comes from it. As a result, only four atoms of oxygen 17 are present in a million atoms of oxygen sample.

Chamberlain, who helped process samples at the Terrestrial Paleoclimate lab at Stanford, said, “There are maybe eight labs in the world that can do this analysis. Still, it took us three years to get numbers that made some sense and worked daily.”

Yuan Gao, Jingen Dai, and Chengshan Wang at the China University of Geosciences funded this research.

Journal Reference:

  1. Daniel E. Ibarra, Jingen Dai, et al. High-elevation Tibetan Plateau before India–Eurasia collision recorded by triple oxygen isotopes. Nature Geoscience. DOI: 10.1038/s41561-023-01243-x
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