On February 6, Geophysical Research Letters, the flagship publication of the American Geophysical Union and one of the journals included in Nature Index, published online the research paper titled A Smaller Greater India and a Middle–Early Eocene Collision With Asia by Jin Shuchen, Ph.D. candidate of the College of Resource, Environment and Tourism, CNU, and other students.

The Indo-Asian continental collision is one of the most important orogenic events in the Phanerozoic Eon, which still affects the global climate, ecology and biological diversity. The collision between India and Asia triggered the change of global land-sea and geomorphic patterns since the Cenozoic Era, and has contributed significantly to the global warming process in the last 50 million years. The time and mode of the initial collision between India and Asia are the premise and basis fordiscussing the formation and evolution of the Himalayan orogenic belt and the uplift of the Tibetan Plateau, which has long been controversial in the earth science community.

The discussion of the collision between the Indian and Asian continents cannot be separated from the size of the Indian Plate before the collision. The Indian Continent is still subducting under the Asian Continent, which causes frequent earthquakes and other natural disasters in this region. Since the Cenozoic Era, part of the Indian Continent has been subducted under the Asian Continent. Thesubducted and compressed part is called the Great Indian Plate (Greater India for short)(Figure 1). Quantitative estimation of the size of Greater India is the key to understanding a series of geodynamic processes such as the time of the collision between the Indian and Asian continents, the subduction degree of the Indian Plate, the crustal deformation and compression degree, and the Himalayan orogeny. However, the size of Great India is still very controversial in the earth science community. The size of Greater India determined by different methods ranges from some hundred kilometers to 3,000km, which restricts the study of the time and mode of the initial collision between the Indian and Asian continents.

Funded by the Key Research Project of the National Natural Science Foundation of China, Jin Shuchen et al. conducted tectonic paleomagnetic, rock magnetic, andpetrographic studies on the marine sedimentary limestone of the Zongpu Formation in the Tethys Himalaya in Tingri during the mid Paleocene Epoch. Results showed that the size of Greater India was only about 900km (Figure 1) and that theTethys Himalayan did not separate from the Indian Plate during the late Cretaceo-Eocene Epoch. The existence of the Neo-Tethys Ocean (Figure 2a) stretching about 2,000km between the Indian Continent and the Lhasa Block on the southern edge of the Asian Continent 60 million years ago challenges the common understanding that the initial India-Asia collision occurred during this period. Over 60-50 million years ago, the Indian Plate drifted at an average rate of 160±28 mm/a, meaning that the northern edge of Greater India (e.g. Dingri, Gyantse, Gamba, and Zanska) collided with the southern edge of the Asian Continent almost simultaneously about 50 million years ago, followed by the quasi-synchronous closure of the once-existing Neo-Tethys Ocean in the equatorial region (Figure 2b). This finding provides a key direction for determining the time and nature of the India-Asia collision, and provides a new starting point for the study on global climate change, biodiversity, geographical environment during the Cenozoic Era and the structure of the Asian Plate.

Figure 1 Location (the yellow part, while the dotted part represents its present location) and Size of Greater India About 60 Million Years Ago

Figure 2 Reconstructed Geographical Environment During the Collision between the Indian and Asian Continents (KLA: The Kohistan–Ladakh Arc)

This research was jointly funded by the Key Research Project of the National Natural Science Foundation of ChinaThe Kinematic Research on the Lhasa Block and the Tethys Himalayan during the Collision between the Indian and Asian Continents(91855216), and the General Science and Technology Project of the Beijing Municipal Education Commission Paleomagnetic Constraints during the Collision between the Indian and Asian Continents (KM202210028012).

Link of the paper: https://doi. org/10.1029/2022GL101372