MESO-CENOZOIC VOLCANICS IN JILIN PROVINCE AND THEIR TECTONIC SETTINGS

Jilin province is located at the castern margin of the Eurasian plate.Since the Mesozic,two volcanic rock associations have been erupted.They possess the characteristics of inheritance and development in both magmatic activity and tectonic settings.The Mesozoic Volcanics are represented by a basalt-andesiterhyolite association occurring in the continental-margin down-faulted basin Mountain tectonic setting,while the Cenozoie Volcanics include an alkaline olivine basalt tholeiite-quartz trachyte association occurring in the continentmargin,rift valley-fracture tectonic setting.The distribtion of the Mesozoic volcanics in the study area is controlled by the northeast-trending subparallel faultfold structures.These structures resulted from sinistral shearing due to the northwestward subdnction of the Pacific plate beneath the Eurasian plate.The formation of the volcanics was affected by the operative pattern of the subduction zone,but it is the only factor. The distribntion of the Cenozoic volcanic in the area is controlled by the structures which inherited the Mesozoic tec- tonic framework and further transformed into extensional rift valley-fracture structures.The fromation of the volcanics was not affected by the operative pattern of the subduction zone.The Mesozoic volcanics in the area are dominated by andesites,which were derived from the andesitic magma,and some rhyolites and basalt andesites resulted from partial differentiation of the andesitic magma and its contamination with the country rocks.In the Cenozoic volcanics basalts are predominant with some quartz trachytes and pantellerites which the products of differentiation of the basaltic magma.Both the andesitic and the basaltic magma are the products of partial melting of the upper mantle.