鄂尔多斯盆地东北部构造热演化史的磷灰石裂变径迹分析

运用磷灰石裂变径迹(AFT)分析的构造热年代学研究方法,系统探讨鄂尔多斯盆地东北部不同区段中新生代以来的热演化历史,为盆地东北部石油和天然气等多种沉积能源矿产的勘探预测提供新的约束条件。模拟结果表明:盆地东北部经历了250~150 Ma缓慢埋藏增温过程,平均增温速率为0.9℃/Ma;150~120 Ma为快速增温阶段,平均增温速率高达2.1℃/Ma,地层温度达到最高,且均大于130℃。之后不同区段经历差异降温过程:北缘露头区经历了120~65 Ma快速降温,平均冷却速率约1.3℃/Ma;65~10 Ma缓慢降温,平均冷却速率约为0.4℃/Ma。南缘露头区及盆地沉降区则经历了120~30 Ma缓慢降温,平均冷却速率约为0.9℃/Ma;30~10 Ma快速降温,平均冷却速率约为1.5℃/Ma。10 Ma以来,盆地东北部整体抬升冷却,平均冷却速率约6.5℃/Ma。分析结果认为燕山中期构造热事件之最高热增温作用的关键时刻为(120±10)Ma,促成鄂尔多斯盆地东北部主要烃源岩层系的成熟生烃和大规模油气成藏。在后期的差异抬升冷却过程中,北缘露头区在65 Ma±通过了110℃等温面,南缘露头区及盆地的沉降区在30 Ma±通过了110℃等温面,有利于相邻地区原生油气藏的积聚和保存,古近纪晚期(30 Ma)尤其是新近纪晚期近10 Ma以来的强烈构造抬升作用有可能是引发原生油气藏调整—改造和次生成藏的关键因素。

Apatite Fission Track Analysis of Tectono-thermal History in the Northeast of Ordos Basin

Apatite fission-track analysis offers the opportunity to reveal Meso-cenozoic tectono-thermal history of different sections and different sequences in the Northeast of Ordos Basin,and to provide new constraints on forecast and prospect oil,gas and other mineral.Simulation results show that: the temperature of stratum slowly rose at the rate of 0.9 ℃/Ma during 250-150 Ma;and rapidly rose at the rate of 2.1 ℃/Ma during 150-120 Ma in the northeast of Ordos Basin.At this time,all temperatures that are higher than 130 ℃ reach the highest.After that,strata of the north margin in the northeast of Ordos Basin rapidly uplift and cool at the rate of 1.3 ℃/Ma during 120-65 Ma and slowly uplift and cool at the rate of 0.4 ℃/Ma during 65-10 Ma;and strata of the south margin and subsidence of basin slowly uplift and cool at the rate of 0.9 ℃/Ma during 120-30 Ma and rapidly uplift and cool at the rate of 1.5 ℃/Ma during 30-10 Ma.The northeast of basin rapidly uplift and cool at the rate of 6.5 ℃/Ma since at least 10 Ma.Therefore,it is considered that(120±10) Ma is the key time of Mid-Yanshan tectonic thermal event,which brought about the mature hydrocarbon generation and the large-scale petroleum accumulation in the northeast of Ordos Basin.The north margin passed the 110 ℃ closed temperature in the 65 Ma±,and the south margin and subsidence area passed 110℃ closed temperature in the 30 Ma±,which were beneficial to the proto-petroleum enrichment and preservation.Since Paleogene late(30 Ma),especially Neogene late(10 Ma),the rapid uplift-cooling process has most probably become the key factor of the proto-petroleum adjustment and the secondary reservoir formation.