Qinghai-Tibet Plateau: Telling you the secret of my "growth"

The Third Pole

Before it became what it is today,

In fact, one has developed

Low altitude warm valley

Over a period of more than 20 years, with the support of the Second Qinghai-Tibet Scientific Expedition, the collision uplift and impact team led by Ding Lin, an academician of the Chinese Academy of Sciences and a researcher at the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences (hereinafter referred to as the Qinghai-Tibet Plateau Institute), has described the appearance and historical process of the low-altitude "Central Valley" before the uplift of the Qinghai-Tibet Plateau through comprehensive research in multiple fields and methods, including tectonic geological evolution, deep structure of the lithosphere, paleoaltitude, paleotemperature, paleovegetation analysis and paleoclimate simulation. The relevant research was published in the journal Science Advances on February 10.

The “low point” before the rise

The uplift process of the Qinghai-Tibet Plateau is complex

And has gone through a long historical period

The geodynamic process of its uplift

Still controversial

Some people believe that

During the Eocene Epoch, between 53 and 36 million years ago, the southern part of the plateau first reached the highest altitude and then rose northward.

Another view is that

In the Eocene, the central part of the plateau was the highest area in terms of altitude, forming the prototype of the Qinghai-Tibet Plateau. Then, starting from the Miocene, it expanded southwards into the Himalayas and northwards to the Kunlun Mountains and Qilian Mountains in the northern part of the Qinghai-Tibet Plateau.

Xiong Zhongyu, the first author of the paper and a doctor from the Qinghai-Tibet Plateau Institute, said that after the collision between the Indian Plate and the Eurasian Plate, a "low-altitude central valley" completely different from the current landform developed between the tall Gangdise orogenic belt and the Central Divide orogenic belt. It runs from west to east along the current Ritu-Gezhe-Nima-Bange-Nagqu-Dingqing line.

"But we don't know yet when did it rise to its current height and what was the endogenous driving force that caused the uplift of the Central Valley." Ding Lin said that accurately quantifying the uplift process and characteristics is crucial to assessing its impact on the atmosphere and surface processes.

Since 1997, Ding Lin has led his team to conduct field surveys in the Lunpola Basin in the middle of the Central Valley, trying to solve this mystery.

The Lunpola Basin belongs to Bange County, Tibet Autonomous Region. It covers an area of ​​about 3,600 square kilometers, with an altitude of about 4,700 meters, an annual average temperature of about 0°C, and an annual precipitation of 400-500 mm. It has a typical high-cold monsoon climate and is a hot spot for studying the uplift history, mechanism and environmental-biological effects of the Qinghai-Tibet Plateau.

Ding Lin led the team to conduct a field survey in the Lunpola Basin in the middle of the Central Valley

Image source: Institute of Tibetan Plateau Research, Chinese Academy of Sciences

Finding the "code" in volcanic ash

The volcanic ash layer is the

Deposited

Ash from ancient volcanic eruptions

Can be used to accurately define

Formation era and absolute age of strata

Absolute age of the strata

Similar to a "ruler"

Only on the basis of this yardstick

Researchers can accurately

Reconstructing the evolution of the Earth's various spheres

The research team discovered a total of 9 sets of volcanic ash in the basin. Using the zircon uranium-lead dating method, they determined the absolute age of the volcanic ash and established an absolute age framework for the sedimentary strata in the Lunpola Basin 50-20 million years ago.

Studies have shown that the lower Niubao Formation was deposited between 50 and 29 million years ago, and the upper Dingqing Formation was deposited between 29 and 20 million years ago.

Zircon U-Pb ages of volcanic tuffs in the Lumpola Basin. Light blue circles indicate the Concordia age of each sample. (A) Cretaceous Madden Formation volcanic rocks. (B) Tuffs of the upper part of the lower Niubao Formation. (C-E) Tuffs of the middle Niubao Formation. (F) Tuffs of the lower Dingqing Formation. MSWD, mean square weighted deviation. (G) Tuffs of the middle Dingqing Formation. (H and I) Tuffs of the upper Dingqing Formation. Image source: Science Advances

Based on this chronological framework, the research team collaborated with the paleoclimate simulation team of the University of Bristol in the UK and used the paleoclimate simulation method on the Qinghai-Tibet Plateau for the first time. They determined that the rainfall pattern in the central valley of the Qinghai-Tibet Plateau is a bimodal pattern in winter and summer.

At the same time, combined with rainfall, surface evapotranspiration and soil moisture content, the formation season of paleosol calcareous nodules was revealed: the formation time of paleosol calcareous nodules in the lower Niubao Formation was March to June, while the formation time of paleosol calcareous nodules in the upper Niubao Formation was limited to two stages: May to June and September.

The deep circle is the "endogenous driving force"

Based on the ancient surface temperature determined by isotope data of ancient soil calcareous nodule clusters, the research team also creatively used the surface air wet-bulb temperature and the wet-bulb air temperature lapse rate to quantitatively restore the history of surface height changes in the Lunpola Basin.

(Figure A) During the late Eocene to early Oligocene, the valley floor rose rapidly by about 2.4 to 2.7 kilometers at a rate of 0.24 to 0.27 mm per year. Central Tibet may have reached its current height in the late Oligocene (Figure 7B) Image source: Science Advances

The research results show that about 50-38 million years ago, the Qinghai-Tibet Plateau presented a geomorphic feature of "two mountains sandwiched by a basin", with the Gangdise Mountains at an altitude of about 4,500 meters and the Central Divide Mountains at an altitude of about 4,000 meters, sandwiched between them is the Central Valley at an altitude of about 1,700 meters. The Central Valley has a warm and humid climate, with precipitation dominated by westerly winds and monsoons, and subtropical flora and fauna flourishing, making it the "Shangri-La" inside the plateau.

About 38-29 million years ago, the central valley represented by the Lunpola Basin rapidly uplifted into a plateau with an altitude of more than 4,000 meters, which also marked the formation of the main part of the Qinghai-Tibet Plateau.

With the uplift of the Central Valley and the cooling of the global climate, the temperature in the central part of the plateau has dropped significantly, precipitation has decreased, and the monsoon effect in the south has been relatively strengthened. Climate change has caused the central part of the plateau to change from a warm and humid subtropical ecosystem to a cold and dry alpine ecosystem, with alpine meadows as the main surface vegetation.

Combined with the team's previous research, the results further pointed out that the time when the orogenic belt to the north of the Yarlung Zangbo suture developed into the main body of the plateau was the late Eocene-Early Oligocene (38-29 million years), while the Himalayas to the south of the Yarlung Zangbo suture only reached its current height in the early Miocene (25-15 million years).

Ding Lin introduced that the deep geodynamic mechanism that led to the uplift of the Central Valley was the subducting Lhasa mantle delamination, the upwelling of asthenosphere materials and the shortening of the upper crust. The uplift of the Central Valley marked the beginning of the great impact of the Qinghai-Tibet Plateau on the surface environment.

The study opened up

Sphere isolation and scientific boundaries

In the Qinghai-Tibet Plateau

Research on spatiotemporal evolution

A solid step forward

On the Qinghai-Tibet Plateau

Earth System Science Research

Has an important demonstration role

—THE END—

Source: China Science Daily Producer: Ma Lian Editor: Wu Nan

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