松辽盆地南部白垩纪裂后期异常沉降分离

Differentiation of Anomalous Cretaceous Post-Rift Subsidence in the Southern Songliao Basin

为了研究松辽盆地白垩纪裂后期沉降的动力机制,以松辽盆地南部长岭、十屋凹陷为例,用回剥法和应变速率反演方法对研究区钻井和地层剖面资料进行了研究。结果表明：观测得到的裂后沉降和模拟预测的理论裂后沉降结果存在较大差异,异常沉降量达160-800 m;并且异常沉降经历了两次沉降高峰期,分别出现在裂后期的泉头组及嫩江组沉积时期,平均沉降速率最大值出现在泉头组沉积时期,达16 m/Ma,同期地壳应变速率也达到裂后期最大值,约为6 Ga^-1。该异常沉降除受到裂后期基底断裂和盆地小型正断层活动的小部分影响外,可能主要受控于中生代晚期Izanagi俯冲板片在松辽盆地深部的下拽作用及其诱发的深部地幔流动,属动力沉降。

To understand the dynamic mechanisms of post-rift subsidence in Songliao Basin,the backstripping and strain rate inversion methods are used to study the stratigraphic sections and boreholes in Changling sag and Shiwu sag on the southern edge of Songliao Basin by analyzing the relevant data.The post-rift anomalous subsid-ence is computed as the discrepancy between observed and predicted post-rift subsidence based on modeling ex-ponential thermal cooling following earlier lithospheric thinning events.The modeling results of 13 wells show clearly that the anomalous subsidence during the post-rift stage is between 160 m and 800 m in the study area. With averagely maximium subsidence rate reaching 16 m /Ma and strain rate reaching 6 Ga^-1 ,the rapid subsid-ence periods in the study area occurred at 99.6 -91.4 Ma（Quantou Formation）and 84.7 -79.1 Ma（Nenjiang Formation）.The Cretaceous anomalous post-rift subsidence in the southern Songliao Basin was primarily in-duced by downdrag pressure of subducting in western Pacific slab and deep mantle flow under Songliao Basin. The basement faulting in Songliao Basin during Early Cretaceous and normal faulting in the post-rift stage also make contribution to anomalous post-rift subsidence.