| 第四纪洞庭盆地澧县凹陷构造活动特征及动力学机制探讨 |
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| 引用本文：柏道远,李长安,王先辉,马铁球,彭云益.2010.第四纪洞庭盆地澧县凹陷构造活动特征及动力学机制探讨[J].地球学报,31(1):43-55. |
| DOI：10.3975/cagsb.2010.01.06 |
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| 基金项目:中国地质调查局地质大调查项目(编号: 1212010610706)和国家自然科学基金项目(批准号: 40672206) |
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| 中文摘要:第四纪澧县凹陷为洞庭盆地西北部的一个次级凹陷。通过地表观察和钻孔资料, 对澧县凹陷及周缘第四纪沉积物和地貌及其反映的构造活动特征进行了研究, 进而探讨构造活动的动力机制。澧县凹陷呈由南、北西、北东边界正断裂所限的三角形。早更新世-中更新世中期, 边界正断裂强烈活动, 凹陷区大幅沉降, 充填了一套以砂砾层为主的沉积, 其厚度自凹陷边缘向中央增加; 正断裂下盘局部存在较大幅度沉降。与此同时, 澧县凹陷南面、西面的外围地区产生构造抬升, 形成由冲积层组成的多级基座阶地。中更新世晚期开始凹陷区及周缘地带整体抬升, 凹陷区北部及凹陷南缘产生自西向东的掀斜, 凹陷区北部形成小型褶皱构造。上述构造活动特征指示澧县凹陷在早更新世-中更新世中期具断陷盆地性质, 中更新世晚期以来具拗陷盆地性质。提出早更新世-中更新世中期构造活动与地幔上隆有关: 深部地幔上涌对地壳加热, 使凹陷区中 地壳韧塑性物质膨胀而向周边侧向迁移, 尔后冷却收缩致上层地壳“塌陷”而产生整体性下拗沉降, 并于下沉块体侧翼发育正断裂。此外, 重力均衡机制可能也起到一定作用。中更新世晚期以来的构造活动可能与深部物质蠕移运动的弹性回返以及板块尺度的物质运动和挤压作用有关。 |
| 中文关键词:澧县凹陷 断陷盆地 拗陷盆地 动力机制 第四纪 |
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| Tectonic Activities and Dynamic Mechanisms of the Quaternary Lixian sag of Dongting Basin |
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| Abstract:Quaternary Lixian sag is a second-order tectonic unit in the northwestern part of the Dongting Basin. The authors studied the Quaternary sedimentary, geomorphic and tectonic characteristics of the Lixian sag and its adjacent areas based on near-surface survey and borehole data, and then probed into the tectonic dynamic mechanism. The Lixian sag is a triangle restricted by three normal faults located respectively along the south, northwest and northeast boundary. During Early Pleistocene-middle Middle Pleistocene, the normal faults moved violently, the sag subsided greatly, the sediments mainly composed of sand and gravel beds became increasingly thicker from the margin to the center of the sag, and local footwall evidently experienced strong subsidence. At the same time, the west and south periphery of the sag rose and the base terraces covered by alluvial deposits were formed. The sag and its peripheral areas rose as a whole since late Middle Pleistocene, when there occurred eastward tilt in northern Lixian sag and in south periphery, and small-sized folds were formed in the northern sag. These tectonic activities suggest that the Lixian sag was a faulted basin during Early Pleistocene-middle Middle Pleistocene and has become a depressive basin since late Middle Pleistocene. The authors hold that the tectonic activities during Early Pleistocene-middle Middle Pleistocene were related to mantle uplift: as the deep uplifting mantle heated the crust in Lixian sag, the ductile matter of the middle curst expanded and moved toward the periphery and then shrank by cooling, which brought about collapse and subsidence of the upper crust, and hence normal faults were formed on the margin of the subsided block. In addition, gravity isostasy might have played a part in the subsidence. The tectonic activities since late Middle Pleistocene were possibly related to the return of the earlier transported matter, the movement of the plate-scale material and the compression. |
| keywords:Lixian sag faulted basin depressive basin dynamic mechanism Quaternary |
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