辽东半岛夷平面发育特征初步探究*

夷平面是一种与长期稳定的构造环境相关联的大尺度地貌景观,将夷平面与风化壳作为整体来研究是现代夷平面研究的主流。为了探讨辽东半岛夷平面的性质、形成环境等发育特征,对该地区的红色风化壳进行地球化学分析和粒度测试。辽东半岛红色风化壳主要出露于半岛东西两侧,厚度多在4 m左右,化学蚀变指数CIA平均值为82.70,ba值((Na₂O+K₂O+CaO+MgO)/Al₂O₃)平均为0.39,S/A值(SiO₂/Al₂O₃)平均为4.86,黏粒含量平均为8.31%。从分析数据可以看出,辽东半岛红色风化壳是下伏基岩原地风化的产物,推测其形成于温暖、湿润的气候条件下,与南方岩溶区红色风化壳相比具有盐基淋溶率低、富铝化程度低和黏化作用弱的发育特征。结合区域地貌特征,认为研究区红色风化壳的发育主要经历了4个阶段: (1)岩溶作用在古侵蚀基准面之上的整个岩体内进行,地貌起伏逐渐增大;(2)地貌起伏达到最大,覆盖型岩溶、灰色风化壳开始发育;(3)岩溶双层夷平面基本形成;(4)灰色风化壳的发育近乎停止,原本位于古侵蚀基准面之下的灰色风化壳在构造运动作用下全部抬升于现代侵蚀基准面之上形成红色风化壳。因此,研究区的夷平面为古夷平面,发育阶段为红土化阶段。该研究成果可为辽东半岛新近纪以来的新构造运动及海平面变化研究提供初步依据。

Preliminary study on development characteristics of planation surface in Liaodong Peninsula

Planation surface is one that is associated with long-term stable tectonic environment of large scale landscape. The planation surface with the weathering crust as a whole to study is the main stream of modern planation surface research. The red weathering crust mainly is outcropped in the east and west of Liaodong Peninsula,and its thickness is around 4 m. In order to explore the properties,environment and development characteristics of the planation surface in Liaodong Peninsula,chemical elements and particle size characteristics of red weathering crust in this area were studied. The test results showed that the average value of CIA of the red weathering crust in the study area is 82.70,the average value of ba((Na₂O+K₂O+CaO+MgO)/Al₂O₃)is 0.39,the average value of S/A(SiO₂/Al₂O₃)is 4.86,and the average value of clay content is 8.31%. Compared with the red weathering crust of the karst area in the south of China,it has the characteristics of low leaching rate of salt base,low aluminization degree and weak viscosification. According to the regional geomorphologic features,the development of red weathering crust in the study area mainly went through four stages: (1)karst process was carried out in the whole rock mass above the base level of ancient erosion,and the geomorphologic fluctuation gradually increased;(2)geomorphologic fluctuation reached the maximum,and covered karst and gray weathering crust began to develop;(3)karst double-layer planation surface basically formed;(4)the development of gray weathering crust nearly stopped. With the tectonic movement,the gray weathering crust,which was originally located below the base level of ancient erosion,was all elevated above the base level of modern erosion to form red weathering crust. Therefore,the planation surface in the study area is ancient planation surface,and the development stage is lateralization stage. The results can provide a preliminary basis for revealing the neotectonic movement and sea level change in the Liaodong Peninsula from the Neogene to present.