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通过对洞庭盆地南缘常德-益阳-长沙断裂中段较为详细的浅层物探、钻探、年代学测试以及地表地质地貌调查和综合分析等方面的工作,获得了一些新的认识:常德-益阳-长沙断裂中段(隐伏断裂)表现为一条倾向NNE的正断裂,断错了古近纪基岩顶界面,并向上切错下更新统的华田组(Q1pht)、汩罗组(Q1pm)和中更新统下段新开铺组(Q2px)底界面,而中更新统中段的白砂井组(Q2pb)则平整地覆盖在断裂之上,无任何变形和位错形迹。断裂的最新活动时代在中更新世早期,中更新世中晚期以来已无活动迹象。断裂两盘基岩顶界面(或下更新统底界面)垂直落差(即第四纪以来总断距)为16.10m;越往上断距越小。同一层位,断层上盘的华田组(Q1pht)和汩罗组(Q1pm)的沉积厚度远大于断层下盘的沉积厚度,表明该断裂的活动具有较多的边沉边断的同生性质。以与洞庭盆地南缘常德-益阳-长沙断裂中段对应的安乡-汉寿凹陷为例,通过对第四纪以来断裂控制的差异性沉降幅度与凹陷内沉积厚度的对比分析,初步认为安乡-汉寿凹陷主要是通过拗陷作用形成的,而不是断陷作用。洞庭盆地与周边隆起山地之间不但断裂发育,同时也是中强地震集中发生的地带。一条断裂是否存在断错早、中更新世地层的构造现象,是判断中强地震发震构造的一个重要标志。
Through the more detailed shallow geophysical exploration, drilling, geochronology test, surface geology and geomorphology investigation and comprehensive analysis in the middle section of Changde-Yiyang-Changsha fracture in the southern margin of Dongting Basin, some new understandings have been obtained: Changde-Yiyang-Changsha The middle fault (buried fault) behaves as a normal fault with a tendency of NNE, which breaks down the top interface of the Paleogene bedrock and turns upwards to the Lower Pleistocene Huatan Formation (Q1pht), Miluo Formation (Q1pm) The Q2px bottom interface is formed in the lower section of the Middle Paleozoic, while the Q2pb in the middle section of the Middle Pleistocene is flatly covered above the fault without any deformation or dislocation. The latest episode of faulting has shown no sign of activity since the mid-late Pleistocene and mid-late Middle Pleistocene. The vertical drop (ie the total fault distance since the Quaternary) of the top of the fracture bedrock (or the lower Pleistocene interface) is 16.10m; The depositional thicknesses of the Q1pht and the Milo Formation (Q1pm) in the same layer and the fault upper plate are much larger than the sedimentary thickness of the lower fault, indicating that the fault has more concentric features . Taking the Anxiang-Hanshou depression corresponding to the middle section of Changde-Yiyang-Changsha fracture in the southern margin of Dongting Basin as an example, by contrasting the difference between the settlement control and the sedimentary thickness in the depression since the Quaternary, - Hanshou depression is mainly formed by depression instead of rifting. Between the Dongting Basin and the surrounding uplifted mountains, not only faults develop, but also concentrated areas where the strong earthquakes occur. It is an important indicator to judge the seismogenic structure of the moderate-strong earthquakes that whether a fault is fault-ruptured or the middle-Pleistocene stratigraphic phenomenon.