China News Service, Beijing, February 10 (Reporter Sun Zifa) When was the Qinghai-Tibet Plateau, known as the "roof of the world", formed?
When will the Central Valley disappear?
What is its power mechanism?
What kind of historical process has it gone through?
The latest research by the collision uplift and impact team led by Academician Ding Lin from the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences (Institute of Qinghai-Tibet Plateau, Chinese Academy of Sciences) gives the answer.
They quantitatively restored the uplift and extinction process of the central valley of the Qinghai-Tibet Plateau 38 million to 29 million years ago through comprehensive research on tectonic geological evolution, deep lithosphere dynamics, paleotemperature, paleovegetation analysis, and paleoclimate simulation. , revealing that the uplift of the Central Valley is the beginning of the huge impact of the Qinghai-Tibet Plateau on the episphere environment.
This important scientific research paper on solving the mystery of the formation of the roof of the world on the Qinghai-Tibet Plateau was published online by the international academic journal Science Advances on February 10, Beijing time. It has an important demonstration role in the scientific research of the Earth system of the Qinghai-Tibet Plateau, and has also become an important achievement of China's second comprehensive scientific expedition to the Qinghai-Tibet Plateau.
The process of uplift and demise of the central valley of the Qinghai-Tibet Plateau 38-29 million years ago.
Photo courtesy of Institute of Qinghai-Tibet Plateau, Chinese Academy of Sciences
9 sets of volcanic ash found in Lumpola Basin
According to the Institute of Qinghai-Tibet Plateau of the Chinese Academy of Sciences, after the collision between the Indian plate and the Eurasian plate, a low-altitude central valley, which is completely different from the present landform, developed between the tall Gangdise orogenic belt and the central watershed orogenic belt. It runs from west to east. The current Japanese-Tu-Gai-Ze-Nima-Bango-Naqu-Dingqing line is extended.
In order to unravel the mystery of the deep geodynamic mechanism leading to the uplift of the Central Valley and the endogenous driving force of the plateau surface layer, the team led by Academician Ding Lin has been studying the history, mechanism and environmental-biological effects of the uplift of the Qinghai-Tibet Plateau since 1997. The hotspot area of China—Lumpola Basin, Bangor County, in the middle of the Central Valley, carried out field investigations. So far, 9 sets of volcanic ash have been found in the Cenozoic strata in the basin, and rich animal and plant fossils have also been exposed in the strata.
The research team used the zircon uranium-lead dating method to determine the absolute age of the volcanic ash, and established the absolute age frame of the sedimentary strata of the Lumpola Basin 50 million to 20 million years ago. Previously, the depositional age of the upper strata was 29-20 million years ago.
On the basis of this chronological framework, the research team cooperated with the paleoclimate simulation team of the University of Bristol in the United Kingdom, and for the first time used the method of paleoclimate simulation to determine that the rainfall pattern in the central valley of the Qinghai-Tibet Plateau is bimodal in winter and summer, combined with rainfall Quantity, surface evapotranspiration and soil moisture content, etc., reveal the formation season of paleo-soil calcareous nodules.
In addition, the research team creatively used the surface air wet-bulb temperature and the wet-bulb temperature lapse rate to quantitatively recover the history of surface height changes in the Lumpola Basin.
Academician Ding Lin led the team to conduct field investigations in the Lumpola Basin.
Photo courtesy of Institute of Qinghai-Tibet Plateau, Chinese Academy of Sciences
"Two mountains and one basin" uplifted into a plateau over 4,000 meters above sea level
Dr. Xiong Zhongyu, the first author of the paper and the Institute of Qinghai-Tibet Plateau of the Chinese Academy of Sciences, said that the research results show that about 50 million to 38 million years ago, the Qinghai-Tibet Plateau presented a landform feature of "two mountains and a basin". The Gangdise Mountains were about 4,500 meters above sea level, The Central Divide Mountains are about 4,000 meters above sea level, and between them is the Central Valley, which is about 1,700 meters above sea level.
The climate in the Central Valley is warm and humid, and precipitation is dominated by westerly and monsoons.
The co-author of the paper and researcher Su Tao of the Xishuangbanna Botanical Garden of the Chinese Academy of Sciences believes that the subtropical animals and plants in the Central Valley are prosperous, and it is the "Shangri-La" inside the plateau.
About 38 million to 29 million years ago, the Central Valley represented by the Lunpola Basin rapidly uplifted into a plateau over 4,000 meters above sea level, marking 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 dropped significantly, the precipitation decreased, and the monsoon effect in the south was relatively enhanced.
Climate change has led to the transformation of the central plateau from a warm and humid subtropical ecosystem to a cold and dry alpine ecosystem, and the main surface vegetation has evolved into alpine meadows.
The range of the central valley of the Qinghai-Tibet Plateau (white shaded area) and the change profile of the surface height. The five-pointed star represents the location of the Lunpola Basin, the study site.
Photo courtesy of Institute of Qinghai-Tibet Plateau, Chinese Academy of Sciences
Plateau Growth Process Driven by Deep Cycling on the Qinghai-Tibet Plateau
Academician Ding Lin, the corresponding author of the paper, pointed out that the deep geodynamic mechanisms leading to the uplift of the Central Valley are the subducting Lhasa mantle demolition, the upwelling of asthenospheric materials, and the shortening of the upper crust.
The plateau growth process driven by the deep sphere action of the Qinghai-Tibet Plateau is the endogenous driving force for the evolution and chain response of the plateau surface layers (atmosphere, cryosphere/hydrosphere, biosphere and anthroposphere).
Combined with the team's previous research, the latest results further show that the time for the development of the orogenic belt to the main body of the plateau was the Late Eocene-Early Oligocene (38-29 million years ago) north of the Brahmaputra suture, while the Brahmaputra suture The Himalayas south of the line did not reach their current heights until the early Miocene (25-15 million years ago).
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