松辽盆地南部无机CO_2成藏机理与分布

Distribution and Accumulation of Inorganic CO_2 in Southern Songliao Basin

松辽盆地南部的幔源CO2气主要存在3种脱气方式:热底辟体脱气、岩浆房脱气和地幔热底垫体脱气。古近纪末—新近纪时期的岩浆活动和岩石圈断裂是无机CO2气藏形成的主控因素;属于岩石圈断裂的郯庐断裂北部断裂系,当处于活动期时,诱导幔源岩浆上涌,促使无机CO2气从幔源岩浆脱出,先期富集在下地壳底部,并沿着下地壳的网状剪切带迂回向上运移到达拆离带;当断至拆离带的低角度基底断裂处于活动期时,无机CO2气体沿着壳源断裂上移进入地壳浅层圈闭富集成藏。气源断裂体系的展布与幔源火成岩活动脱气是无机CO2气运聚成藏的两大主控因素。幔源CO2气藏主要分布在长岭断陷和德惠断陷:前者主要沿着孙吴—双辽断裂带分布,后者受控于哈尔滨—四平断裂带。长岭断陷的幔源CO2气藏埋藏较深,由于向北西的红岗阶地和东部的德惠断陷层位在变新,导致CO2气藏埋藏深度逐渐变浅。

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.