OPHIOLITES AND ULTRAHIGH PRESSURE ZONES IN THE CENTRAL OROGENIC BELT OF CHINA: TECTONIC HISTORY OF A COMPOSITE OROGENIC BELT

The Central Orogenic belt (COB) between the North China (NCB) and South China blocks (SCB) represents the northernmost orogenic collage of the Tethys domain that experienced a series of early Paleozoic and early Mesozoic subduction-accretion events, and an intracontinental orogenic event in the Cretaceous. It is bounded by the early Paleozoic tectonic belt in the north (N-COB) and the early Mesozoic tectonic belt in the south (S-COB). The North Qilian and the North Qinling oceanic-type suture zones, the North Qaidam continental-type suture zone and the east Kunlun arc-type suture zone in the western segment of N-COB indicate multiple events of terrane accretion via subduction-collision processes in the early Paleozoic (550-420 Ma). The North Qilian and the North Qinling orogenic belts form a continuous, early Paleozoic suture zone between the NCB and SCB as evidenced by (1) the occurrence of rock assemblages of common origin and ages, with similar tectonic structures, and (2) southward getting younger multiple arc terranes accreted to the continental margin between 540 Ma and 450 Ma as small forearc basins collapsed and closed. Following the closure of the Proto-Tethys Ocean in the Carboniferous, the A’nyemaqen-Mianlue basin evolved into a small ocean separating the south Qinling micro-plate from SCB. The discovery of two phases of UHP metamorphic zones in the early Paleozoic (505-440 Ma) and early Mesozoic (240-220 Ma) segments of COB reveals that both the NCB and SCB experienced deep oceanic/continental subduction processes in the early Paleozoic and Triassic, respectively.