Neotectonism In Changchun-Siping Area

The paper is based on three scientific projects: first, ecological environmental geologic investigation in Siping area with a scale of 1:50000, imbursed by the Ministry of Land and Resources; second, appreciation of regional crust stability and investigation on geological hazards in Jilin province, imbursed by the Planning Commission of Jilin province; third, classification of agricultural farmland and its application in supplement and equilibrium of agricultural farmlands in different fields, imbursed by the Ministry of Land and Resources. The author studied the neotectonism in Changchun-Siping area.Most of the neotectonics in Changchun-Siping area are fractures, and they are successional. Such as northeastern Siping-Changchun fracture, northeastern Yilan-Yitong fracture, northwestern Zhanyu-Wohutun fracture, northwestern Nanxianmaquan fracture, northwestern Dahongzui -Fangniugoukou fracture and eastwestern Hujiawobao-Xibada fracture. The neogenic fractures are both crust and cover fractures, and their scales are small. For example, southnorthern Dafuling fracture, west-north-western Kongdayuan-Hejiaxinzi fracture etc. Mercury-surveying in the soil cross these fractures shows peak value over them. And along some fractures, such as Kongdayuan-Hejiaxinzi, there are some springs. These phenomenons reflect that the fractures are active.From west to east, the research area includes Songliao plain, Daheishan horst, Yitong-Shulan graben and eastern Jilin fault-block mountains and it is a classical basin-ridge morphostructure, and the landforms in the east are higher than that in the west. According to their origin, there are two types of geomorphy, one is morphostructure, and the other is ectodynamorphic geomorphy. There are three classes and ten types in form. The first class includes Songliao plain and Hadaling fault-block mountains. The second class includes horsts and grabens. The third class includes taphrogenic and alluvial plain, tilted and alluvial plain, volcanic cone, fault valley, intruded rock hills and hog-back highland. There are two types of ectodynamorphic geomorphy, gravity geomorphy and stream geomorphy.The main types of gravity geomorphy are surface flow geomorphy, flood geomorphy and stream geomorphy.The paper analyses the grain-size features of the loess at Xingshan town and the result shows its features:(l) The size classification is bad and the main grain size( ) is greater than 7.61 (0.005 mm) . The average of grain size is between 7.61 and 8.26 (0.005 mm~0.003 mm) . (2) The composition of grade is as follows: sand 44.75%, silt 31%, and clay soil 24.25%. (3) The major frequency curve is single-peaked and positive. Binding the features of the other sediments, authors presume that the loess was accumulated in mid and late Pleistocene. The first genesis of the loess is sand dune and it was loessificated, so the loess was formed under the condition of tropical climate during the interglacial period. The neotectonism of research area is the main influencing factor for the accumulation of the loess.The neotectonism not only made the ground water surface descended and aggravated the process of desertification, but also offered the space and situation for the accumulation of the loess.The main volcanic and seismic activities are developed along northeast Siping-Changchun and Yilan-Yitong lithospheric fractures, and they are strictly controlled by them. The main volcanoes are distributed in Yitong and Fanjiatun-Datun areas. The Yitong volcanic group is distributed in Yitong-Shulan graben and arranged parallel along the graben's sides. The majority of the volcanoes are located at the intersections of two active fractures (zones). They erupted sequentially, the oldest is Xijianshan volcano with a age of 21.0Ma, the youngest is Xishan volcano at Dagushan with a age of 7.78Ma. According to the data of the deep source inclusion and chemical analysis, the author pursued the analyze of the unary linear regression and got a formula for the relation between the depth of magma source(y) and the content of...