ULTRAMAFIC ROCKS IN THE DONGHAI AREA,NORTHERN JIANGSU

Ultramafic rocks in Doughal, northern Jiangsu, fall into two belts. The northern beltconsists dominantly of metaperidotite,while the southern belt ultramafic cumulates of oceanic crust. They are dismembered ophiolites. It is inferred that the ophiolites originated in an ocean basin between the northern Jiangsu-Jiaonan terrane and the Jiaobei terrane on the northern margin of the Meso-to Neoproterozoic Yangtze paleocontinental plate. Metaperidotite isrepresented by relict mantle peridotite resulting from moderate degrees of fusion of primarypyrolite at high P/T. Ultramafic cumulates are the product of partial melting of primary pyrolite or magmatic crystallization differentiation,enriched in garnet and associated with eclogite,and are relatively low-temperature, ultrahigh-pressure metamorphic rocks formed in theprocess of southward subduction of oceanic crust in the Meso-to Neoproterozoic. They hadundergone strong fracturing and were thus squeezed into different tectonic levels in the lowerpart of the Donghia Group complex and became deep-seated blocks in melanges of the Doughal subduction zone.