Compound orogeny and scientific problems concerning the Central Orogenic Belt of China

Abstract：Orogenic belts widely distributed in the Earth have recorded the history of plate convergence and orogenic processes during the collision. Many of these belts are long-lived (>300 Ma) compound belts, which are more than 1000 km wide with a pre-orogenic thermal structure that provides evidence for continental growth. In the past decade, research has begun to focus on the long-term dynamics of such belts as well as their tectonic features and processes. A number of critical problems remain existent, which include the origins of the long-term activities, the mechanism of continental accretion, and the rheological and thermal structure of such orogens. The Central Orogenic Belt of China (COB) is a huge compound orogen, which extends more than 5000 km across central China and marks the boundary between the North China Block and the South China Block. The COB has been active for ~600 Ma, and during this time it underwent two major collisions, one in the Devonian and the other in the Triassic. In addition, the region has become tectonically active since the Cretaceous. The COB differs from other compound orogens in having a very complex structure, multiple long-term orogenic events, convergence of orogens and accretion of continents. The recent discovery of a large high- and ultrahigh-pressure metamorphic belt (HP-UHP) in the orogen and the recognition of two HP-UHP metamorphic events indicate the subduction of both oceanic and continental crust to the depth greater than 100 km. Thus, the COB is as important in the tectonic evolution of Asia as the Qinghai-Tibetan Plateau. Some of the critical unanswered questions regarding the COB include the nature of the continental convergence, collision and orogeny in the Devonian and Triassic and the formation of intracontinental sedimentary basins during the Mesozoic and Cenozoic. Also unclear are the temporal and spatial relationships of the HP-UHP metamorphic belts and the conditions under which deep subduction and exhumation of oceanic/continental crust took place. Likewise, the processes responsible for the long-term tectonic activity, the multiple and overlapping orogenies, and the thermal structure of the region are unclear. In addition, little is known about the genesis of the mineral deposits in the region and the oil and gas potential of adjacent Mesozoic and Cenozoic basins.