THE PETROGENESIS OF THE SPILITE-KERATOPHYRESEQUENCE OF THE HAIZHOU GROUP IN NORTHERN JIANGSU

The matavolcanic rock sequence of the Hiazhou Group in northern Jiangsu,consistingmainly of quartz keratophyre with subordinate spilite and rare keratophyres,belongs to aspilite-quartz keratophyre association type and is characterized by a generally higherK content.On the basis of analyses of the petrography,petrochemistry and REE contents ,it is material ofsubmarine eruption in the Haizhou rift trough an intracontinental rift formed under inter-mediate conditions during the Late Proterozoic. Spilite and quartz keratophyre were derivedfrom alkali basaItic magma of the upper mantle and subalkaline rhyoritic magma of the sialiccrust respectively,so show the features of a bin1odal model. After the deposition of the HaizhouGroup, regional medium-and high-pressure greenschist facies metamorphism occurred severaltimes. Three metamorphic facies zones may be distinguished :the glaucophane greenschist facieszone ,Iow greenschist facies zone and high greenschist facies zone,showing a progressive meta-morphism.