China News Service, Tibet, August 2 (Reporter Sun Zifa) Why is the Qinghai-Tibet Plateau, known as the "roof of the world" and "the third pole of the earth", at different heights?
How did it form?
The Continental Collision and Plateau Uplift Team led by Academician Ding Lin from the Institute of Tibetan Plateau Research, Chinese Academy of Sciences was invited by the editor-in-chief of the international professional academic journal "Natural Review: Earth and Environment". ” published a review paper, systematically revealing the differential uplift process and deep dynamic mechanism of the Qinghai-Tibet Plateau.
The research team pointed out that the uplift of the Qinghai-Tibet Plateau driven by deep spheres such as continental collision-subduction is one of the most important geological events in the Cenozoic era.
Plateau uplift has significantly affected the coupling process of episphere-atmosphere, hydrosphere/cryosphere, biosphere and anthroposphere, and profoundly affected Asian climate dynamics, biodiversity, carbon cycle, modern water resources distribution and large rivers. It is the frontier of earth system science research in the 21st century.
65-45 million years ago, "two mountains and one basin" landform.
Photo courtesy of the Continental Collision and Plateau Uplift Team
However, the mechanism of continental lithospheric deformation and spatiotemporal changes in surface elevation on the Qinghai-Tibet Plateau during continental collision remains unclear.
In recent years, with the accelerated production of quantitative paleo-altitude data on the Qinghai-Tibet Plateau, scholars have gradually realized that the plateau has the characteristics of differential uplift, and the uplift time of some areas is earlier or later than previously estimated. Neither can fully reflect the plateau uplift process.
Cretaceous tectonic events and the prototype of the Qinghai-Tibet Plateau mountain range
Academician Ding Lin emphasized that the complete evolution model of the Qinghai-Tibet Plateau must take into account the heterogeneity of paleogeomorphology and lithosphere inherited by Asia in the tectonic events prior to the Indo-Eurasia collision, which is crucial for understanding the differential uplift of the plateau. .
45-40 million years ago, "two mountains and one basin" landform.
Photo courtesy of the Continental Collision and Plateau Uplift Team
A terrane is a complex of crustal fragments or crustal fragments bounded by faults and has a unique geological history.
Through a detailed analysis of the Cretaceous sea-land transition, tectonic deformation, magmatic and low-temperature thermochronological evidence on the Qinghai-Tibet Plateau, the research team proposes that the collision of the Lhasa-Qiangtang terrane and the subsequent northward subduction of the Lhasa lithosphere led to the initial growth of the Watershed Mountains; The continuous subduction of the southern Neo-Tethys Ocean uplifted the Gangdise area to the sea level about 95 million years ago, forming a development process similar to that of the present-day Andes, which is called the Andean-type Gangdise. And form a significant precipitation effect in southern Tibet.
At this time, the Qinghai-Tibet Plateau had only two narrow mountain ranges, the Dividing Range Mountains and the Gangdise Mountains, but the magnitude of the surface uplift remains to be quantified.
Timing and Mode of Initial Indo-Eurasia Collision
40-30 million years ago, the unified plateau was formed.
Photo courtesy of the Continental Collision and Plateau Uplift Team
The research team said that the timing and manner of the collision of the Indo-Eurasian plates are crucial for limiting the extent of the northern Indian margin and the amount of deformation in the Cenozoic intracontinental shortening, which in turn are the keys to constrain the magnitude of the plateau's surface uplift and deep dynamics.
At present, the hypotheses about the closure history of the Neo-Tethys include the Great Indian Ocean Basin model, the intra-ocean subduction model, and the single-stage subduction collision model. The foreland basin formed by continental collision, which began to receive provenances from the Gangdise island arc between 65 million and 59 million years ago, indicating that India-Eurasia had begun to collide at this time, much earlier than previously recognized internationally. The time when India and Eurasia initially collided 50 million years ago.
30-25 million years ago, the plateau grew outward.
Photo courtesy of the Continental Collision and Plateau Uplift Team
At the same time, the team of Academician Ding Lin has also gained key insights from their work in Tibet, Pakistan and India in the past 20 years: First, the Gangdise magma arc, fore-arc basin, ophiolite and ocean trench currently developed in southern Tibet were formed in the southern Lhasa terrane. The second is the evidence from northern Pakistan that Asian material could reach the Indian subcontinent about 52 million years ago, which does not support the existence of an ocean before the Indo-Eurasia collision. Bowl.
Therefore, the newly published paper states that the single-stage subduction collision model is the simplest to explain the Indo-Eurasia collision and is supported by geological evidence.
But unfortunately, paleomagnetic data show that if the Indo-Asian continents collided about 60 million years ago, the Indian and Asian continental lithospheres must have absorbed about 4,000 kilometers of crustal shortening in a fully continental setting.
However, current geological evidence indicates that the Asian (less than 1000 km) and Himalayan (less than 1000 km) crustal shortening is less than 2000 km.
25-15 million years ago, the modern plateau was formed.
Photo courtesy of the Continental Collision and Plateau Uplift Team
In order to coordinate the mismatch between crustal shortening and paleomagnetic convergence, international scholars have proposed the Great Indian Ocean Basin model and the intra-ocean subduction model, but both lack the support of geological evidence.
In addition, if the Indian continent has undergone a counterclockwise rotation of about 90 degrees during the northward drift, it can also simply absorb the 2000-kilometer latitudinal shortening.
Different orogenic belts of the Qinghai-Tibet Plateau have different uplift histories
The team of Academician Ding Lin believes that the need to solve the uplift history of the plateau has greatly promoted the development of paleoaltimeters. The widely used paleoaltimeter quantitative reconstruction techniques include hydrogen/oxygen isotopes, animal and plant fossils, and cluster isotopes.
These paleo-altitude quantitative reconstruction techniques provide key information for continental deformation and plateau growth, and can provide a clearer understanding of the differential uplift process and dynamic mechanism of the plateau.
Combining the existing quantitative paleo-altitude results and deep dynamical evidence, the research team further restored the surface uplift history and lithospheric evolution process of different terranes on the Qinghai-Tibet Plateau from about 60 million years ago to the present, and proposed that different orogenic belts of the Qinghai-Tibet Plateau have different Uplift History:
Between 55 million and 45 million years ago, the Gangdise orogenic belt was uplifted to an altitude of 4500 meters due to the break-off of the subducting slab of the Neo-Tethys Ocean.
45 million to 40 million years ago, after the Neo-Tethys plate broke off, the more buoyant Indian lithosphere wedged horizontally to the north, activating the intracontinental subduction of the north-south suture zone of the Qiangtang terrane, causing the watershed mountains to uplift. At this time, the central valley between the Gangdise orogenic belt and the watershed orogenic belt, the Himalayan orogenic belt in the southernmost part of the plateau, and the northern part of the plateau are still at a low altitude of less than 2000 meters. A basin" geomorphological features.
40 million to 30 million years ago, the Lhasa lithosphere was demolition and sinking under the Central Valley, and the coupling of various deep geodynamic processes, such as the shortening of the upper crust, the magma bottom cushion, and the upwelling of the asthenosphere, made the Central Valley uplift 4,500 meters. At this height, the Qinghai-Tibet Plateau has been officially transformed from an orogenic belt to a unified plateau.
25-15 million years ago, due to the continuous subduction of the Indian continent, the lithosphere of the Indian continent subducted under the Himalayas and the lithosphere of the Eurasian continent subducted under the Hoh Xil-Kunlun Mountains in northern Tibet were demolition and sinking successively. Uplifted to modern heights, a plateau in the modern sense was formed.
The team of Academician Ding Lin pointed out that, however, the uplift history of the northern Qinghai-Tibet Plateau still has great uncertainty, and more quantitative paleo-altitude data is needed to verify.
The uplift of the Qinghai-Tibet Plateau needs to focus on four research directions in the future
Indo-Eurasia initial collision model.
Photo courtesy of the Continental Collision and Plateau Uplift Team
The team of Academician Ding Lin said that geophysical exploration revealed that the lithosphere of present-day India and Eurasia has undergone various geodynamic behaviors ranging from horizontal wedging to steep subduction, plate tearing, breaking off, and demolition. Throughout the Cenozoic India-Asia continental collision, similar processes continued to occur, which eventually led to the spatial and temporal differences in the tectonic deformation, magmatism and surface uplift of the Qinghai-Tibet Plateau.
Regarding the follow-up research on the uplift time and mechanism of the Qinghai-Tibet Plateau, the team of Academician Ding Lin believes that four research directions need to be developed in the future:
One is to resolve the inconsistency between the Indo-Eurasian convergence and crustal shortening; the second is to accurately define the uplift history of the plateau by a large amount of high-resolution paleo-height data; the third is to combine numerical simulations and geological data to accurately reconstruct the plateau Earth System evolution history; Fourth, combined with geophysical imaging technology and geodynamic simulation, clarify the circulation process and distribution range of the continental lithosphere, and analyze how continental collision affects the structure of adjacent plate boundaries and global-scale mantle convection.
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