OPHIOLITES OF THE KUNLUN MOUNTAINS, CHINA AND THEIR TECTONIC IMPLICATIONS

Three ophiolite belts, ranging in age from Cambrian to Triassic, provi de valuable data on the tectonic evolution of the Kunlun Mountains whi ch lie along the northern margin of the Tibetan Plateau. All of the op hiolites contain dismembered but nearly complete assemblages of perido tite, mafic and ultramafic cumulates, pillow and massive lavas and rad iolarian cherts. (1) The oldest belt contains ophiolites of Cambrian a ge, but the initial spreading of the ocean basin most likely began in the Late Proterozoic. These ophiolites outcrop in the central part of the eastern Kunlun, extend for at least a few hundred kilometers, and are believed to reflect a small ocean basin. Closure of this ocean led the accretion of south Kunlun block to the north Kunlun block and Tar im craton. Ophiolitic lavas in this belt have island are affinities. ( 2) A second belt of early Carboniferous ophiolites extends nearly 600 km along the northern margin of the western Kunlun. Lavas in this belt are basalt, basaltic andesite and andesite, all of which have composi tions characteristic of volcanic arcs. This ocean basin possibly devel oped on the basis of the early Paleozoic oceanic basin. Closure of thi s ocean basin by southward subduction in the early Permian produced a suite of calc-alkaline volcanic rocks in what is now the central part of the western Kunlun. (3) The third belt extends nearly 1200 km along the southern margin of the Eastern Kunlun and contains numerous ophio lites of Early Permian to Middle Triassic age. These ophiolites are hi ghly tectonized, containing volcanic rocks with the geochemical charac teristics of mid-ocean ridges, oceanic islands and volcanic arcs. This belt is tentatively interpreted as the suture zone between Gondwana a nd Eurasia.