Thursday, February 7, 2019

Is Mount Kailash The Oldest Mountain In The Himalaya?

No. It is not.

Although, according to this tweet it is.


The person tweeting as CBG-san (@OnlyNakedTruth) uses Pranay Lal's book Indica: A Deep Natural History Of The Indian Subcontinent as the source (page 268-269), and also refers to an analysis done on Mount Kailash rocks. I could not make out the source of the table of analysis. They show the age of Mount Kailash Formation as ranging from around 30 million years to around 10 million years old.

Let me get one technical point out of the way. Geologically,  Mount Kailash is not in the Himalaya. It is part of  the Asian continental plate. These mountains are known as the Transhimalaya. Locally, these ranges are also called the Gangdese Shan. The Himalaya are the deformed and uplifted rocks of the Indian plate. This is a quibble though. I appreciate that the larger point is whether the rocks of Mount Kailash were uplifted very early during the India-Asia collision process.

The Mount Kailash range is made up of thousands of feet of sediment of the Kailash Formation, sitting on 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, magmas formed deep inside the Asian plate. Blobs of this magma rose and solidified in the subsurface 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 on top on this granite. 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 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. 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 of these lakes, which geologists speculatively place between 1000 m to 3500 m. Presently,  Kailash Basin sediments are exposed at altitudes greater than 6000 m.

The graphic below shows the depositional environment of the Kailash Formation


Source: DeCelles et.al. 2016- Oligocene-Miocene Great Lakes in the India-Asia Collision Zone

The rocks that make up Mount Kailash are younger than 26 million years. They formed nearly 30 million years after the collision of the Indian and Asian continents.

High topography 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 methods of estimating elevation also suggest high elevations in this region by  35-40 million years ago. The ratio of the two isotopes of oxygen (O18 to O16), bound in calcium carbonate minerals,  is temperature dependent. Measurements from southern Tibet indicate paleo-elevations of around 5000 m by 35 million years ago.

Second, the zone of India-Asia collision (Indus-Tsangpo Suture), 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 (which later was uplifted to form the Siwalik ranges) began receiving sediment derived from the erosion of the newly uplifted Himalaya.

Eocene age (45-35 million years) sediments in this foreland basin contain rock fragments and minerals inherited from the Indus-Tsangpo Suture and the Tethyan Himalaya. Younger foreland sediments of Early Miocene age (between 24 and 15 million years) contain fragments of the Tethyan Himalaya as well as the newly emerging Greater Himalaya.

The timing of uplift of the Greater Himalaya is also hinted at by geochronology. The radioactive clock inside muscovite (a type of mica) starts ticking below around 350 C. Clocks in other minerals like zircon (zirconium silicate) and monazite (rare earth phosphate) are set at higher temperatures, at 700 C and 600 C respectively. A sample may contain all three of these minerals, as Greater Himalayan granites and gneisses often do. Their dates of formation track a cooling history, as the rock is uplifted from deeper crustal levels to shallower regions.

Such work by geologists 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 formation of topography. Mike Searle's book Colliding Continents: A geological exploration of the Himalaya, Karakoram, & Tibet describes these different methods for assessing rock ages and cooling histories.

A different geochronology method known as fission-track dating,  that measures radiation damage in crystals of zircon (zirconium silicate) and apatite (calcium phosphate) to estimate when the rock cooled below 200 C to 100 C indicates that the Kailash Formation was uplifted later than 17 million years ago.

Ranges on the Asian continent (Gangdese Shan), as well as the Indus-Tsanpo Suture in the collision zone and the Tethyan Himalaya belt to the south on the Indian plate, are older than Kailash. The Greater Himalaya was uplifted around the same time as the Mount Kailash Formation.

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.


I've always been struck by a disconnect in Pranay Lal's book. His end notes are detailed and summarize the state of research fairly well. However, there are many basic mistakes in the main text. I made a list of the many geology errors in his book in an earlier post titled Book: Indica- A Deep Natural History of the Indian Subcontinent.

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 or Transhimalaya.  Mount Kailash's classic pyramidal shape evolved during the ice ages of the Quaternary Period beginning 2.58 million years ago, when glaciers dug out valleys and cut back slopes, forming smooth sided and sharp edged peaks.

2 comments:

  1. Very good article.
    P.S: I sent you an email today re-introducing myself.

    ReplyDelete