黄土高原及邻区新构造与新构造运动

中国黄土高原及邻区可划分为六个构造地块和构造接合带,其中央主体部分为一具中等强度活动性的环状构造,2.4Ma以来垂直运动幅度为930—1000m,平均速率为0.39—0.42mm/a。新构造运动可划分为四个主旋回、三个主幕。1.67MaB.P.前后构造应力场由近南北向转为近东西向。黄土-古土壤系列和水系沉积物-古土壤系列可作为新构造运动新的时间标尺。

NEOTECTONICS AND NEOTECTONIC MOVEMENT OF THE LOESS PLATEAU AND ITS ADJACENT REGIONS

The Loess Plateau of Northwestern China has been regarded as a stable land block surrounded by some active tectonic belts and its neotectonic features therefore have scarcely been submitted to thorough practical investigations. In this dissertation we have arrived at new conclusions on the basis of the data set composed of over 10 000 individual pieces gathered by the author from more than 600 profiles spreading over the plateau and another 5 000 pieces from more than 400 profiles accumulated in the literatures. The conclusions on the neotectonics are as follows: 1. The loess-paleosols and hydrogenic sediments-paleosols sequences are new time-scales for evolution of the neotectonics. 2. The Loess Plateau is not so stable as it has been thought. It has mid activity intensity. The plateau and its adjacent regions may be divided into 6 blocks (micro-plates) and 6 tectonic joint zones, and a ring rotation structure is found located in its central part. 3. Since 2.4 Ma B. P. the maximum vertical amplitute of the neotectonic movement is 930—1 000m and its average rate is 0.39—0.42mm/a in the central part of the plateau, but in the active tectonic belts (as between the Helan Mountains and the Yinchuan Basin) around the plateau it is 2 750m and 1.15mm/a. 4. The neotectonic movement is divided into 4 main cycles, the ages (Ma B. P.) of which are >3.5—2.4, 2.4—1.67, 1.67—0.1 and 0.1—0. There are 3 main generations in the neotectonic movement and their ages (Ma B. P.) are 2.4 or so, 1.67—1.45 and 0.1 or so. The synchro periodicity appeared between the main neotectonic cycles and the main climatic cycles. 5. The tectonic stress fields had undergone constant changes. The principal compressive stress with the position about S-N appeared before 1.67 Ma B. P., but the position had been transferred into direction NE-SW after 1.67 Ma B. P. The change is closely related with the movements of the India, the Pacific and the Eurasia Plates and the movements of the earth as a plannet during Late Cenozoic Era. Many facts from stratigraphy, geomorphology, tectonics, microtectonics, structural geology, volcanology, chronology and climatology are enumerated in this paper, and figures and tables are attached for illustration.