摘要:
Yin'e Basin,located in western Inner Mongolia,has undergone multiple tectonic alterations since its formation in the Paleozoic.The Yanshan tectonic movement resulted in that the basin experienced the tectonic evolution of intracontinental basin and generated a series of oil sags,such as Chagan depression and Juyanhai depression during the Cretaceous.However,tectonic evolution of the oil sags needs to further address.The study on apatite fission track of the five wells in the Xirehada region,northwestern margin of Yin'e Basin,has revealed the tectonic evolution history of the study area during the Mesozoic.The central fission track ages of 8 samples range from 111±8 Ma to 140±8 Ma and the track lengths range from 12.1±1.9 μm to 12.8±2.2μm.The track lengths in these samples is characterized by single peak and negative bias,reflecting that during the late Jurassic and early Cretaceous,the study area underwent tectonic uplifting and erosion event due to influence of curtain Ⅲ of the Yanshan movement.The study area was dominated by uplifting during this period.Based on the vitrinite reflectance of some drilling samples in study area,the denudation thickness of Middle Lower Jurassic ranges from 1069.06 to 2503.73m,suggesting that the area underwent strong uplifting and oil system was destroyed at this time.The results of thermal history of 8 samples,simulated by Hefty software,also indicate that the study area reached the maximum burial depth before Late Jurassic,followed by a rapid uplift and apatite annealing temperature range,about 120°C,during 140 ~111Ma.Since then,temperature decreased very slowly and continued to maintain the upper limit of annealing temperature,i.e.oil threshold temperature,until 60~40Ma,from then to now there has been no strong tectonic uplifting.Consolidate works of Yagan region,in the middle Yin'e Basin,and Shangdan depression,in the eastern Yin'e Basin(apatite fission track age is 90~113Ma,129~159Ma),it can be recognized that differential uplifting may develop in Yin'e basin during the Mesozoic,besides,influence of tectonic movements on different tectonic sites may vary from period to period,which is favorable to the study of tectonic evolution for Yin'e Basin.Combined with the previous work in the Yagan area and Shangdan depression in the eastern Yin'e basin (especially the age of 90~113Ma and 129~159Ma by apatite fission track),this study confirmed that differential uplifting of the Yin'e basin occurred in the Mesozoic period and different structural positions also show different change due to various tectonic movement,both providing evidence for study of tectonic evolution of the Yin ' e basin.%银额盆地位于内蒙古西部,自古生代形成之后经历了多期次构造改造.燕山期构造运动使盆地经历了陆内盆山构造演化,并在白垩纪孕育了查干凹陷、居延海凹陷等一系列的生油凹陷,这些生油凹陷的构造演化过程还有待进一步研究.本文通过对银额盆地西北部希热哈达地区(居延海凹陷)的5口钻井开展磷灰石裂变径迹研究,揭示了研究区中生代构造演化史.8个样品的中心年龄为111±8~140±8Ma,径迹长度在12.1±1.9~12.8±2.2μm之间,各样品径迹长度分布具有单峰、负偏的特征.反映了在晚侏罗世—早白垩世时期,受燕山Ⅲ幕构造运动影响,研究区遭受抬升、剥蚀的构造事件.该时期是研究区主要抬升期,根据研究区部分钻井样品的镜质体反射率恢复中下侏罗统剥蚀厚度在1069.06~2503.73m之间,证明该时期抬升强烈,油气系统遭受破坏.同时,利用Hefty软件对8个样品开展的热史模拟较为一致地反应研究区在晚侏罗世之前达到最大埋深,之后在140~111Ma之间经历了短暂的快速抬升,进入磷灰石退火带温度范围(120°C左右).此后较长时间内温度保持极为缓慢的降低,直至60~40Ma退出退火温度上限即生油门限温度,并持续至今,期间并无强烈的构造抬升.结合与银额盆地中部雅干地区和东部尚丹凹陷所开展工作(磷灰石裂变径迹记录年龄为90~113Ma,129~159Ma),证明银额盆地中生代时期存在差异隆升,不同构造位置受不同期次构造运动的影响也存在差异,为银额盆地构造演化研究提供了依据.