HR: 0800h
AN: S41B-0977    [Abstracts]
TI: Seismogenic Structure of the Northern Section of Lijiang Basin in Northwest Yunnan (China) in Quaternary
AU: * Zhujun, H
EM: Xuhan928@263.net
AB: Located at the middle of Jinshajiang-Red River fault zone and intersected by Xiaojinhe fault zone, Lijiang region in northwest Yunnan, China, is surrounded by a complex dynamic environment. The northern section of Lijiang basin (NSLB) has the features of a zigzag fault, a kind of `tracing extension' in the shape. Taking the west boundary as example, it can be divided into three segments, among which south segment is in the N-S trending, central segment in the NNE trending and north segment becomes the N-S trending again. Basin width changes regularly along the basin boundary. The central part in the NNE-trending is narrow and has an average width of 3.5km. Both the south and north parts are wide and have an average width of 4.5km, which is 1km larger than that in the central part. It is an important character about a zigzag fault zone with a component of shear displacement. Fault slip is characterized mainly by extension, and sinistral shear. Average sinistral-shear and spreading displacements are respectively 1950m and 1730m. The kind of movement began in middle Pleistocene, which is about 800ka ago. Average sinistral and extensional slip-rates can be acquired, which are 2.44mm/a and 2.16mm/a. Geological evidences at different segments of Lijiang basin demonstrate results of geomorphic analysis, and are in consistent with our knowledge about the zig-zag fault. The field observation at the north segment of the NSLB shows a vertical displacement of 25 to 27m and a sinistral displacement of 12.5 to 13.7m, which happened after 9 to 10ka B.P. Based on the conclusions, it can be acquired that the average vertical slip rate of boundary fault in the NSLB in Holocene is 2.74mm/a and the average horizontal slip rate is 1.38mm/a. Sinistral displacement of ridges and gullies are very typical around Longquan in the middle of the west boundary in the NSLB. 29m sinistral displacement of a gully and 16m vertical offset of alluvial, diluvial and remnant deposits in late Pleistocene can be recognized at the north of the Longquan village. Based on the above analysis about structural geology, two conclusions about kinematic features in the NSLB can be acquired. One is that the tectonic movement in the NSLB is characterized by sinistral shear and extension and the other is that the components of vertical and horizontal movements are different at the different segments of the NSLB. The component of the vertical movement is clearly larger than that of the horizontal component in the N-S-trending segments, but it is contrary in the NE or NNE-trending segments in the middle of the NSLB. The phenomena are identical to the kinematic features of a zigzag with a component of shear displacement and the results concluded from the analysis of tectonic-geomorphology in the NSLB. Realization about sinistral shear and extension of the northern section of Lijiang basin provides direct evidence for the model of clockwise rotation of northwest Sichuan active block and the understanding of dynamic features of Red River fault zone.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1217 Time variable gravity (7223, 7230)
DE: 8107 Continental neotectonics (8002)
SC: Seismology [S]
MN: Fall Meeting 2005