Dabie Shansulu Tongbai Central China Orogen

The Qinling-Dabie-Sulu, or Dabie Shan, is the world's largest ultrahigh pressure metamorphic belt, containing Triassic (220-240 Ma) high-pressure, low-temperature (eclogite) facies metamorphic rocks formed during the collision of the North and South China cratons. Most remarkably, the orogen contains coesite and diamond-bearing eclogite rocks, indicating metamorphic burial to depths exceeding 60 miles (100 km). The Dabie Shan metamorphic belt stretches from the Tanlu fault zone between Shanghai and Wuhan, approximately 1,250 miles (2,000 km) to the west northwest to the Qaidam basin north of the Tibetan Plateau. The orogen is only 30-60 miles (50-100 km) wide in most places, and it separated the North China craton on the north from the Yangtze craton (also called the South China block) on the south. A small tectonic block or terrane known as the South Qinling is wedged between the North and South China cratons in the orogen and is thought to have collided with the North China cra-ton in the Triassic, before the main collision.

The Qinling-Dabie-Sulu orogen is marked by numerous terranes forming the irregular suture between the North China and South China cratons. It is a major part of the E-W-trending Central China orogen that extends for 900 miles (1,500 km) eastward from the Kunlun Range, to the Qinling Range, and then 370 miles (600 km) farther east through the Tongbai-Dabie Range. Its easternmost extent, offset by movement along the Tan-Lu fault system, continues northeastward through the Sulu area of the Shandong Peninsula then into South Korea. The Sulu belt may extend through the southern part of South Korea. The intermittent presence of ultrahigh-pres-sure diamonds, eclogites, and felsic gneisses indicates very deep subduction along a cumulative 2,500-mile (> 4,000-km) long zone of collisional orogenesis.

The rifting and collisional history throughout the Paleozoic of the North China and Tarim cra-tons with blocks and orogens to the south, such as the North Qinling terrane, the South Qinling ter-rane, and eventually (in the Triassic) the South China craton, have been complicated and controversial. In the early Paleozoic northward subduction of the Qaidam-South Tarim plate (possibly connected with the South China plate) took place beneath the active southern margin of the NCC. The North China cra-ton, probably together with the Tarim block, collided with the South Tarim-Qaidam block in the Devonian, then with the South China block in the Permo-Triassic. This latter collision resulted in exposure of ultrahigh-pressure rocks from approximately 60-120 miles (100-200 km) depth in the Dabie Shan, and westward sliding or escape of the South Tarim-Qaidam block, and caused uplift of a large plateau (Huabei Plateau) in the eastern North China craton. Younger extrusion tectonics related to Himalayan collisions farther west resulted in approximately 300 miles (500 km) of left-lateral motion along the Altyn-Tagh fault, separating the North China craton from the South Tarim-Qaidam block, slicing and sliding to the west the arc that formed on the southern margin of the craton during early Paleozoic subduction.

The terrane accretion and eventual "continent-continent" collision along the southern margin of the North China and Tarim cratons are defined by a geometrically irregular suture, defining a diachronous convergence with a complex spatial and temporal pattern. Many models of extrusion tectonics, such as eastward, vertical (upward), and lateral, have been proposed for the Qinling-Dabie orogen in the last decade. Vertical movement along a paleosubduction zone was important to Triassic uplift of the ultra-high-pressure rocks in the eastern part of the orogen. An orogen-parallel, eastward extrusion occurred dia-chronously between 240 and 225-210 Ma. Cretaceous to Cenozoic unroofing was initially dominated by eastward tectonic escape in the early Cretaceous and then by Pacific subduction in the mid-Cretaceous. The Triassic Dabie high-pressure (HP)-UHP metamorphic rocks were originally located beneath the Foping dome, located in the narrowest part of the Qinling belt, and these rocks were extruded eastward to their present-day location.

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