Tectonic evolution of the Tongbai-Hong'an orogen in central China: From oceanic subduction/accretion to continent-continent collision

The Tongbai-Hong'an orogen is located in a key tectonic position linking the Qinling orogen to the west and the Dabie-Sulu orogen to the east. Because the orogen preserves a Paleozoic accretionary orogenic system in the north and a latest Paleozoic-Mesozoic collisional orogenic system in the south, it may serve as an ideal place to study the tectonic evolution between the North and South China Blocks. The available literature data in the past 20 years indicate that the tectonic processes of the Tongbai-Hong'an orogen involved four stages during the Phanerozoic: (1) Early Paleozoic (490-420 Ma) oceanic subduction, arc magmatism and arc-continent collision created a new Andean-type active continental margin on the North China Block; (2) Late Paleozoic (340-310 Ma) oceanic subduction and accretion generated separated paired metamorphic belts: a medium P/T Wuguan-Guishan complex belt in the south of the Shandan-Songpa fault and a high P/T Xiongdian eclogite belt in the northern edge of the Mesozoic HP metamorphic terrane; (3) Latest Paleozoic-Early Mesozoic (255-200 Ma) continental subduction and collision formed the Tongbai HP terrane in the west and the Hong'an HP/UHP terrane in the east as a consequence of deep subduction towards the east and syn-subduction detachment/exhumation of the down-going slab; (4) Late Mesozoic (140-120 Ma) extension, voluminous magma intrusion and tectonic extrusion led to the final exhumation of the Tongbai-Hong'an-Dabie HP/UHP terrane and the wedge-shaped architecture of the terrane narrowing towards the west. However, many open questions still remain about the details of each evolutionary stage and earlier history of the orogen. Besides an extensive study directly on the Tongbai-Hong'an orogen in the future, integrated investigation on the "soft-collisional" Qinling orogen in the west and the "hard-collisional" Dabie-Sulu orogen in the east is required to establish a general tectonic model for the whole Qinling-Tongbai-Hong'an-Dabie-Sulu orogenic belt.