Hu Fangyang et al.-GRL: Using whole-rock Sr/Y and La/Yb ratios to quantitatively estimate the paleo-altitude changes of the Tibetan Plateau from the Cretaceous to the present. The study of the paleo-altitude of orogenic belts has always been an important part of the study of orogenic belt evolution and paleoclimate.

At present, the commonly used method for calculating ancient altitude is through paleontological fossil records and stable isotopes, such as ancient animal and ancient plant fossils, hydrogen-oxygen isotopes or clustered isotopes of carbonates, etc.

However, both methods rely on sedimentary rocks, so it is difficult to obtain chronological data that directly correspond to ancient heights, and it is difficult to apply to ancient orogenic belts in the pre-Cenozoic.

In recent years, some scholars have used the geochemical composition of magmatic rocks to calculate the ancient height of orogenic belts. However, these methods may be difficult to directly apply to other orogenic belts, or require given variable values, thus increasing the uncertainty of the results.

As the "roof of the world", the Qinghai-Tibet Plateau is the area where ancient height research is most concentrated.

According to paleontological fossil records, the uplift of the Tibetan Plateau mainly occurred in the Miocene, and stable isotope calculations show that the Tibetan Plateau may have uplifted to more than 4,000 meters in the Eocene.

There are currently many views on the uplift model of the Tibetan Plateau, including overall simultaneous uplift, south-to-north stage/continuous uplift, and differential uplift.

In addition, research on the ancient height of the "Tibetan Plateau" before the India-Eurasia plate collision is still blank due to limitations in research methods.

In response to the above problems, postdoctoral fellow Hu Fangyang of the State Key Laboratory of Lithospheric Evolution of the Institute of Geology and Geophysics, Chinese Academy of Sciences, and academician Wu Fuyuan, a co-supervisor, established a relationship between the altitude of global orogenic belts and the Sr/Y and La/Yb ratios of magmatic rocks.

Related equations were used to calculate the paleo-height changes of the Tibetan Plateau from the Cretaceous to the present, and the calculation results were verified.

Considering the difference in average crustal density between the island arc zone and the collision zone, the author established relevant equations suitable for the island arc zone and the collision zone respectively (Fig. 1).

Figure 1 (a, c, e) The relationship between the altitude of global modern island arc zones and crustal thickness, whole-rock Sr/Y ratio and (La/Yb)N ratio of magmatic rocks.

(b, d, f) The correlation between the altitude of the global modern collision zone and the crustal thickness, Sr/Y ratio and (La/Yb)N ratio. The author calculated the ancient height changes of the Tibetan Plateau from the Cretaceous to the present based on the equation (Fig.

2).

The results show that the South Qiangtang Block and the North Lhasa Block began to gradually uplift in the Early Cretaceous.

Entering the Late Cretaceous, the Northern Lhasa Block was uplifted into an ancient plateau (Northern Lhasaplano), and the altitude of this ancient plateau exceeded that of the Gangdese Arc in the same period.

The Gangdese arc experienced a tectonic collapse in the Late Cretaceous (75-70 Ma) and began rapid uplift during the Paleocene.

During the Eocene-Oligocene period, the Qiangtang block experienced significant uplift and basically reached a height of 5000 m.

The paleoheight of the South Lhasa Massif (Gangdise) was relatively stable in the early Eocene, and subsequently uplifted from the late Eocene to the Oligocene, reaching a height of 5000 m.

However, during the Eocene-Oligocene period, the central Tibetan Plateau (Central Lhasa and North Lhasa Massifs) had a relatively low altitude (2500 m), indicating the existence of a valley in the central Tibetan Plateau during this period.

After entering the Miocene, with the uplift of the central Tibetan Plateau to 5000 m and the rapid uplift of the Himalayas, the Tibetan Plateau as a whole has basically reached its current altitude, indicating that the Tibetan Plateau has been basically formed in the Miocene.

Figure 2 Paleoheight changes in various blocks of the Tibetan Plateau from the Cretaceous to the present. The above calculation results are basically consistent with the existing stable isotope calculation results, and are consistent with the research results of regional sedimentary records, structural records, and thermochronology, indicating that this method can be used

The calculated paleoheight evolution of ancient orogenic belts is reliable.

In addition, the results of this study show that the Tibetan Plateau has experienced a complex differential uplift history since the Cretaceous, which provides certain support for further research on the orogenic dynamic process and regional climate effects of the Tibetan Plateau.

The research results were published in the authoritative international academic journal Geophysical Research Letters.