川滇块体东北缘晚第四纪区域气候-地貌分析及其构造地貌年代学意义

地貌年代是新构造特别是活动构造定量研究的瓶颈问题。通过对川滇块体北东边界构造带所在的区域气候变化过程和地貌研究成果的综合分析,利用众多的年代学数据,从区域尺度对地貌的年代、形态和物质组成等特征对比分析,探讨了该区冰川地貌、河流阶地和冲洪积扇的演化特征,揭示了区域气候变化与区域性地貌演化存在的内在对应关系。气候变化产生的气温、湿度、降水量等变化控制了该区冰川地貌和流水地貌的演化。区域内冰川地貌主要是末次冰期的产物,对应于末次冰期两个冰阶,河流作用在7～10ka和1～5ka两个阶段改造末次冰期堆积地貌形成相应的侵蚀地貌。主要河流阶地发育对应于降水量剧烈变化的气候过程,其中形成三级阶地面的流水下切作用最强,随后堆积的深厚物质是二级阶地的主体,并一直没有被后期流水下切作用蚀穿,与气候变化的强度等特点对应。区内冲洪积扇主要有3个堆积时期,即3～5ka,7～10ka和20～25ka,主要发育在气候变化最剧烈的时期,大量的碎屑物形成并短距离搬运堆积。将区域分析综合的结果应运到康定南团结乡附近的地貌分析,可以很好的理解该区的地貌演化,用侵蚀改造的地貌演化结论否认了以前的堆积地貌认识,理清了地貌发育的年龄序列。综合分析与应用的结果表明,区域气候-地貌-构造系统研究对于活动构造年代学具有非常重要的意义。

LATE QUATERNARY CLIMATE AND GEOMORPHOLOGY ON THE NORTHEASTERN MARGIN OF SICHUAN-YUNNAN BLOCK AND THEIR TECTONOMORPHOLOGIC SIGNIFICANCE

As a typical active faulted block of the eastern margin of Tibetan plateau,Sichuan Yunnan block become a key area for active tectonics study. But fast and strong erosion and incision make it a big problem to get enough dating material. In this paper,the regional climate change and geomorphology were analyzed integrally in a regional scale with large quantity of published and our own data. With the analysis on the chronology,landform and sedimentary characteristic,the regional scale characteristics of the evolution of glacial landforms,river terraces and proluvial fans and its relationship with regional climate change were revealed. The results show that the evolution of glacial and fluvial landform was controlled by the changing temperature,humidity and precipitation induced by the climate change. The glacial landform was mainly formed during the Last Glacial,which were corresponding to the two ice stages respectively. The moraine was reconstructed to be eroded landform later during 7～10ka and 1～5ka. The main terraces were developed during the extremely unstable stage of climate change,and six levels of terraces with distinctive character on sedimentation and shape were identified in the study area. Among these terraces,the third level was formed after a strongest fluvial incision,and thick deposition was produced subsequently. This deposition is the main body of the second level terraces and remains uncut through during the following incision. The incision and deposition characteristics after the formation of third level terrace were coincident with the intensive changes of the climate. The proluvial fans were deposited during three stages,3～5ka,7～10ka and 20～25ka respectively,which were the unstable stages of climate,and large quantity of clastic material were produced and transported in a short distance. Finally,the regional geomorphologic evolution model was introduced to the analysis of the landform near Tuanjie to the south of Kangding city. The result provides a good chronologic constrain for the active fault study in this area. The local landforms developed in a manner of reconstruction instead of superposed deposition which was used in former studies. This study suggested that it is of great significance for tectonomorphologic chronology to analyze the regional climate,geomorphology and tectonics systematically.