Qinling orogenic belt

The Qinling orogenic belt is a tectonic feature that evolved throughout the Proterozoic and Phanerozoic eons due to a variety of tectonic activities. It is a part of the Central China Orogenic Belt, aligned in an east–west orientation across Central China, and spans portions of Shaanxi, Henan and Gansu provinces along the Qinling Mountains which are one of the greatest mountain ranges in China. The first materials involved in the Qinling orogenic belt formed around 2.5 billion years ago, whereas the main morphology of the belt now largely reflects the Triassic collision between the North China Plate and the South China Plate and Cenozoic extension across China. During these 2.5 billion years, various types of rocks have been formed here due to different tectonic processes and chemical reactions between rocks. Therefore, geologists are able to reconstruct the evolution of mountain belt based on evidence preserved in these rocks.

Throughout the long history of the evolution of Qinling orogenic belt, there were several cycles of plate collisions and plate separations together with ocean openings and closures occurred. The process is known as a Wilson Cycle. The Qinling orogenic belt was formed largely because of the movements of North China Block and Yangtze Block of the South China Plate.

The Qingling orogenic belt can be divided into two major regions, the North Qinling Belt and the South Qingling belt, which are located at the boundary of the southern North China Craton and the northern South China Craton respectively. The most interesting thing about the evolution of Qinling orogenic belt is the multiple individual micro-block interactions. The tectonic evolution of the whole Qinling belt was not a single event but a combination of several collisional and extensional events, which mainly includes 4 phases:

At the beginning of the Qinling rock record (around 2.5 billion years ago), the North Qinling belt and South Qinling belt were not initially formed together at the same location at the same time. The South Qinling belt was formed by continental magmatic activities 2.5 billion years ago. Then, magma cooled down and became rocks which contribute to the major basement of the South Qinling belt. On the other hand, the North Qinling belt was formed later. It was first formed 1000 million years ago by magmatic activities which occurred in an oceanic-arc environment.

During the early Neoproterozoic (1000 million years ago), the North Qinling belt and the South Qinling were aligned along the same subducting plate boundary at the Northeastern part of super-continent Rodinia (an extremely large tectonic plate composed of different smaller plates). During subduction, the South China block overrode an oceanic plate was compressed and South Qinling belt first formed on a small scale.

On the other hand, the formation of North Qinling belt was more complicated. It did not initially exist with North China Block, but a part of supercontinent Rodinia. At the subducting plate boundary, it collided with Rodinia and was folded up forming North Qinling Belt.

In addition, at some distances further away from the North Qinling Belt, a continental arc with volcanoes was formed at another subducting plate boundary as well, which is named the Proto-Erlangping arc. An arc can be formed because the subducted lower plate melted in the mantle and rose up to the opposite upper plate while cutting through lines of weakness of plate. As a result, magma eventually reached the top of the plate, then cooled down and solidified into rocks, forming an arc. In the meantime, Proto-Erlangping ocean was created at divergent plate boundary where plates separate, so that the Proto-Erlangping arc was moving away from North Qinling belt.

Later on in the middle Neoproterozoic (around 750 million years ago), the supercontinent containing Proto-Erlangping arc, North Qinling Belt and South Qinling Belt was broken up. The two belts were transported to another place together. The oceanic part of South China block was broken and separated into two parts creating the Shangdan ocean. This is because divergent convection magma dominated at that period, when two parts separate, magma rise up from the gap of them creating a larger oceanic plate (as well as an ocean). On the other end of the oceanic plate, it collided with another oceanic plate coincidently. An island arc called 'DanFeng island arc' was formed.