Abstract:

There are three kinds of degassing methods of mantle-derived CO₂ in southern Songliao basin:the mantle thermal diapir, crustal magma chamber, the magma chamber at lowerest crust. Magmatic activity and lithospheric fault leads to the formation of inorganic CO₂ reservoir during the end of Paleogene and Neogene. Mantle-derived magma upwelling caused by geological activity in the northern part of Tan-Lu fault belt which belongs to lithospheric fault, results in the extrusion of inorganic CO₂ from the mantle-derived. Inorganic CO₂ is accumulated at the bottom of lower crust and then raised along network shear belt circuitously to detachment zone. When the low-angle basement fault is at active period which extends to detachment zone, inorganic CO₂ gas migrated to trap and formed gas reservoies along the crustal fault. There are two primary factors controlling concentration and accumulation of the inorganic CO₂ gas reservoir, one is the spread of gas source fault system, the other is the degassing of mantle-derived igneous activity. Mantle-derived CO₂ reservoirs are mainly distributed in the Changling fault depression and the Dehui fault depression, the former is distributed along Sunwu-Shuangliao fault, the later distributed in Harbin-Siping fault. Compared with mantle-derived CO₂ reservoir in Changling fault depression, layers CO₂-bearing in Honggang terrace and Dehui fault depression are younger and shallower.

Key words: Songliao basin, mantle-derived CO₂ reservoir, degassing model, accumulation model