长江口海域新生代地层与断裂活动性初探
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摘要
长江口海域通过浅层人工地震勘察查明 ,新生代地层可分为 5个地震层。分别为第四系、上新统、中新统上段、中新统下段及始新统。第三纪地层自东北向西南依次超覆、减薄尖灭 ,上部被第四纪地层不整合覆盖。沉积基底主要由晚侏罗世火山岩系及燕山晚期酸性小岩体构成 ,未发现早第三纪及晚白垩世断陷盆地。断裂构造很发育 ,按展布方向大体可归为北东、北西及近东西向 3组 ,皆为正断层。前两者数量多、延伸长、断距大 ,与同区的航磁异常构架吻合。北东向断裂分段明显 ,西南段为第四纪断裂 ,中段为晚第三纪断裂 ,东北段为早第三纪断裂 ;而北西向断裂分段不很清晰。两者的垂直位移速率平均在 0 0 1 5mm a。本文对该海域有关的几个地质问题进行了讨论。
By shallow seismic prospecting the Cenozoic Group in the sea area near the Yangtze River Mouth could be divided into five seismic sequences. Those correspond to Quaternary, Pliocene, Upper Miocene, Lower Miocene and Eocene respectively. Quaternary System covers whole detecting area. Tertiary System overlapped and decreased to nip from NE to SW. Sedimentary basement mainly consists of volcanic rock (J 3) and acidic rock (γ3 5). Paleogene or Late Cretaceous basin is not found there. The faults have been detected are all normal faults. They can be divided into three groups (NE, NW, near EW) with trend. The NE and NW-trending faults are predominant, and agree with aeromagnetic anomaly. Their length and displacement are larger than that of EW-trending faults. The activity of the NE-trending faults is different with segment. The SW segment is Quaternary fault, the middle segment is Neogene fault, the NE is Paleogene. But the segment of a NW-trending fault is not obvious. The average vertical displacement rate is about 0.015 mm/a.
By shallow seismic prospecting the Cenozoic Group in the sea area near the Yangtze River Mouth could be divided into five seismic sequences. Those correspond to Quaternary, Pliocene, Upper Miocene, Lower Miocene and Eocene respectively. Quaternary System covers whole detecting area. Tertiary System overlapped and decreased to nip from NE to SW. Sedimentary basement mainly consists of volcanic rock (J 3) and acidic rock (γ3 5). Paleogene or Late Cretaceous basin is not found there. The faults have been detected are all normal faults. They can be divided into three groups (NE, NW, near EW) with trend. The NE and NW-trending faults are predominant, and agree with aeromagnetic anomaly. Their length and displacement are larger than that of EW-trending faults. The activity of the NE-trending faults is different with segment. The SW segment is Quaternary fault, the middle segment is Neogene fault, the NE is Paleogene. But the segment of a NW-trending fault is not obvious. The average vertical displacement rate is about 0.015 mm/a.
引文
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金翔龙,1992,东海海域地质,北京:海域出版社。
江苏省地质矿产局,1984,江苏省及上海市区域地质志,北京:地质出版社。
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