Geological and Geochemical Characteristics of Source Rocks of Carbon Dioxide in Deep Strata of Northern Songliao Basin, Northeast China

Based on studies of major element, rare earth element, fluid inclusion and absorbed gas, the possible source matters of carbon dioxide (CO₂) and their potentialities to form gas accumulations in deep northern Songliao basin, NE China were addressed in this paper. Mantle-Derived magma, volcanic rocks, carbonate rocks and organlc matters are four kinds of potentia1 source matters, whose significances are degressive in turn and vertical distributions could be divlded into shallow, middle, deep and deeper levels. In shallow level, the source matters of CO₂ are volcanic rocks and carbonation rocks with higher total carbon contents and absorbed CO₂ contents, 0 24%-7 76% and 0 213%-1 387% respectively. The absorbed CO₂ contents of volcanic rocks are negatively correlated wlth the S₁O₂ contents, and positively with the Na₂O+K₂O contents. The principal source matters are metamorphic carbonate rocks in middle level and mantle-Derived magma in deep and deeper levels. Higher CO₂ abundance in magmatic systems correspondng to deep volcanic rocks could be suggested by characteristics of lithogeochemistry and fluid inclusion as well as tectonic setting. The volcanic rocks of Yingcheng Formation and corresponding magmatic activities are the most favorable CO₂ source matters in northern Songliao Basin.