The Sciences

Is Mt Kailash the Oldest Mountain in the Himalaya?

The southern margin of the Asian continent was elevated soon after the India-Asia collision, probably by 45 million years ago. But the Kailash Formation did not rise until after 17 million years ago.

In January, Twitter user @OnlyNakedTruth referred to a portion of the book Indica: A Deep Natural History of the Indian Subcontinent, by Pranay Lal, to claim that Mt Kailash was the oldest mountain in the Himalaya.

This author has always been struck by a disconnect in the book, published in 2016. Lal’s endnotes are detailed and summarise the state of research fairly well. However, there are multiple misunderstandings in the main text that lead to inexact conclusions, including with this tweet.

In the present case, @OnlyNakedTruth refers to an analysis performed on rocks from Mt Kailash. The analysis (whose source could not be traced)  shows the age of the sediments making up Mt. Kailash to be between 30 million and 10 million years old.

However, Mt Kailash is not the oldest mountain in the Himalaya.

Let’s get one technical point out of the way. Geologically speaking, Mt Kailash is not in the Himalaya. It is part of  the Asian continental plate. These mountains are known as the trans-Himalaya and, locally, the Gangdese Shan. The Himalaya are the deformed and uplifted rocks of the Indian plate. But this is of course a quibble, and the larger point about whether the rocks of Mt Kailash were uplifted early during the India-Asia collision process is noted.

The Mt Kailash range is made up of thousands of feet of sediment of the Kailash Formation, which sits granitic rocks of the Gangdese batholith. These granitic rocks formed within the southern edge of the Asian continent. As the Indian plate dived underneath Asia, magma formed deep inside the Asian plate. Blobs of this magma rose and solidified under the surface of the Asian continent, forming the Gangdese batholith – a large body of granite. This magmatism took place between 100 million and 45 million years ago.

There are new dates available now for the Kailash Formation, which was deposited atop this granite. The radiogenic dating of lava flows inter-layered with sediment indicates that the Kailash Formation accumulated between 26 million years and 21 million years ago.

This timeline indicates that around, 26 million years ago, the southern margin of the Asian continent and the India-Asia collision zone had subsided. The nature of the sediments indicates that a long chain of lakes formed in narrow depressions. These lakes were receiving sediment eroded from elevated ranges to the north.

The organic matter accumulating in these lakes have been transformed into coal layers. There is also an absence of pollen grains of temperate or high-altitude plant species. This sediment composition points to a lower elevation and warmer water setting, which geologists speculatively place between 1,000 m to 3,500 m. Presently, Kailash Basin sediments are exposed at altitudes greater than 6,000 m.

An illustration of the depositional environment of the Kailash Formation. Source: DeCelles et al, 2016

An illustration of the depositional environment of the Kailash Formation. Source: DeCelles et al, 2016

So the rocks that make up Mt Kailash are younger than 26 million years. They formed nearly 30 million years after the Indian and Asian continents collided.

High topography – i.e. the arrangement of land – already existed along several belts in the collision zone before 26 million years ago.

First, the southern margin of the Asian continent must have been elevated perhaps as early as 45 million years ago, since this terrain was the source of sediment into the Kailash Basin. More direct estimation methods suggest that high elevation existed in this region by 35-40 million years ago.

Additionally, the ratio of two isotopes of oxygen – O-18 to O-16 – in calcium carbonate minerals is dependent on the temperature. Geologists have measured this ratio in southern Tibet to find that paleo-elevations of around 5,000 m existed by some 35 million years ago.

Moreover, the zone of India-Asia collision and the Tethyan Himalaya belt – the northernmost Himalayan ranges – had been uplifted by 45-40 million years ago. The evidence for this comes from the composition of foreland basin sediments to the south. As India collided with Asia, a depression formed in front of the rising mountain chain. This foreland basin, later uplifted to form the Siwalik ranges, began receiving sediment derived from the erosion of the newly uplifted Himalaya.

In the Eocene age, 45-35 million years ago, sediments in this foreland basin contained rock fragments and minerals inherited from the collision zone and the Tethyan Himalaya. Younger foreland sediments of the early Miocene age, between 24 and 15 million years ago, contain fragments of the Tethyan Himalaya as well as the newly emerging Greater Himalaya.

Geochronological techniques have also been able to estimate when the Greater Himalaya came to be uplifted. Radiometric dating is a way to reveal the time at which minerals cool below a certain temperature and stop interacting with their surroundings. This ‘closure temperature is when their radioactive clock becomes stable.

For example, the corresponding radioactive clock of muscovite, which is a type of mica, starts ticking below ~350º C. Clocks in other minerals like zirconium silicate and monazite, a rare-Earth phosphate, start below 700º C and 600º C, respectively.

The Greater Himalayan granites and gneisses often contain all three minerals. So their respective closure dates can be used to trace the history of how they cooled over time, as the rock is uplifted from deeper to shallower regions.

Such studies have shown that the Greater Himalaya were exhumed between 21 million and 16 million years ago. Exhumation in such collisional settings is linked to rapid surface erosion and the formation of topography.

Also read: Any Excuse to Talk About the Himalaya, Both Beauty and Beast

A different method known as fission-track dating, which measures radiation damage in crystals of zirconium silicate and calcium phosphate, estimates when the rock cooled below 200-100º C. This indicates that the Kailash Formation was uplifted later than 17 million years ago.

In sum, the Gangdese Shan on the Asian continent, the Indus-Tsanpo Suture in the collision zone and the Tethyan Himalaya belt to the south, on the Indian plate, are older than Mt Kailash. And the Greater Himalaya was uplifted around the same time as Mt Kailash formed.

This evolution of topography in the Himalaya and along the southern margin of Asia is shown in the schematic below. Orange arrows indicate transport of sediment from source to basin. Black arrows show fault motion.

So it is simply not accurate to say that Mount Kailash is the oldest mountain in the Himalaya. The southern margin of the Asian continent was elevated soon after the India-Asia collision, probably by 45 million years ago. But the Kailash Formation did not rise until after 17 million years ago. It is a much younger component of the Gangdese Shan, a.k.a. the trans-Himalaya.

In fact, Mt Kailash’s classic pyramidal shape evolved during the ice ages of the Quaternary Period, beginning 2.58 million years ago. This is when glaciers dug out valleys and cut back slopes, forming smooth-sided and sharp-edged peaks.

Suvrat Kher is a sedimentary geologist and tweets at @rapiduplift.

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