关键词: 活动断裂, 活动块体, 块体转动, 磁偏角期望值, 磁偏角实测值, 川滇地区

Abstract: The inner part of the Sichuan-Yunnan rhombic block is dissected by the Lijiang-Xiaojinhe Fault, and hence can be subdivided into Northwest Sichuan sub-block in the north and Central Yunnan sub-block in the south. The eastern boundary faults of these two sub-blocks are regularly characterized by left-lateral strike-slip, while the western boundary faults are characterized by right-lateral strike-slip. The slip rate of both the eastern and western boundary faults are significantly different. All these phenomena may indicate the composite movement of these sub-blocks characterized by southeastward horizontal slipping associated with clockwise rotation around a vertical axis during the Cenozoic time. Among them, the horizontal slip rate of the Southwest Sichuan sub-block is 5mm/a, and the angular velocity of clockwise rotation is about 1 4°/Ma, while those of the Central Yunnan sub-block are 3.5mm/a and 1 5°/Ma, respectively. About 90 oriented samples have been collected from Paleogene strata in Yaoan, Dayao, Yongren and Beimajie of Kunming within the Central Yunnan sub-block. The vectors of remanent magnetism of each sample (measured magnetic declination and inclination) have been obtained through alternating field demagnetization and thermal demagnetization. The comparison between the measured magnetic declination and the expected value shows that the accumulated clockwise rotation of the Central Yunnan sub-block of the Sichuan-Yunnan rhombic block since early Miocene has reached up to 30°～48°. The feature represented by the entire rotation of the sub-blocks accompanied by left-lateral slipping along the boundary active faults is consistent with the kinetic model of clockwise rotation of the block in left-lateral strike-slip faulting region.

Key words: active fault, active block, block rotation, expected magnetic declination, measured magnetic declination, Sichuan-Yunnan region