Abstract:

 The last decades have seen a number of studies of Neotectonics in China, concerning with geomorphology, recent sediments and tectonics. The implication of Neotectonics is, however, still controversial up to now. One reason for this is that the lower chronological boundary of the Neotectonic period has been defined as greatly different epochs ranging from the Late Eocene (40 Ma) to the Middle Pleistocene (0.73 Ma). In this work we attempt to address this issue from dynamics of tectonic movements. Analysis of presentday crustal motions, distribution of compressional stress axes of the tectonic stress field and their formation conditions suggests that they are characterized by fairly good continuity and coherence as well as consistent orientations. It indicates that the IndiaEurasia collision is the primary driving force that determines the recent crustal motions and tectonic stress field in mainland China. Geological data shows, however, that in the Eogene time eastern and western mainland China was under extension and compression respectively that were completely distinct tectonic environments. This situation continued till the Middle Miocene (1520 Ma) when the blocks in the eastern Tibetan plateau, such as SichuanYunnan (ChuanDian) and Bayan HaraSongpan, were extruded laterally. These blocks slide from north to south and towards southeast to push eastern mainland China, thus linking eastern and western mainland China together as a united tectonic system. It has caused a series of tectonic events as well as changes of dynamic setting of the Cenozoic in eastern China. All these lines of evidence demonstrate that the neotectonic movements of China started from the  middle Miocene, i.e. about 1510 Ma B.P.

Key words: Neotectonics, lower chronological boundary； Tibetan Plateau； extrusion； Middle Miocene