Abstract: Detailed macro and micro scale structure analyses and finite strain measurements have revealed that there are significant differences in the structure characters in crustal deformation between pre-and post-Mesozoic. Due to the superimposition and reconstruction of later deformation, the pre Mesozoic structures can only be seen with difficulty in the Archenn basement. Since Mesozoic, the area of interest has experienced at least two stages of deformation: the early contraction and late extension. Contraclion: Decolleinent-thrusting caused three levels of structural deformation from lower to up:1 the ductile shear zone represented by mylonile zone developed between metamorphic basement and sedimentary cover；2. the ductile and brittle shear zone developed within the Changlingzi Formation being a relatively weak zone in the cover:and 3. the thrust zone shown by the overthrusting of the Cambrian and Carboniferous strata onto the Jurassic stratum. The middle and lower level structures such as stretching lineation, shear folds. A-type folds. asymmetric rotational porphyroclast and S C fabric both on macro and micro-scale were resulted from the westward decollment. In addition, regional magmatism accompanied this stage tectonic movement suggested that the regional heat flux was relatively high. Extension: This stage deformation occurred at about 118-103Ma accompanying the uplifting of metamorphic basement. It is mainly characterized by ductile normal shear zones and a great number of brittle normal faults developed both in the basement and in the cover. The formation of NNE trending tensile Cretaceous granitoid veins and regional NNE striking Cretaceous basins such as Pulandian Basin, Beihai Basin and Xiongyue Basin had close relation with this deformation—suggesting that the inner and neighbouring areas of the basement were at the tensional environment owing to the uplifting of basement. The development of a great number of felsic veins parallel to the foliation of mylonite in the basement indicates that dynamic partial melting occurred during the ductile shearing. Composition of the fluid inclusion hosted in the felsic veins is mainly H2O with few CO2. Field observation demonstrates that there are two types of felsic veins:syn-decollement type and syn-normal shearing type. The former consists of fewer K-feldspar and more plagioclase and has undergone intensive ductile shearing which can be inferred from the deformation features such as close shear folds and mylonization. While the later has more K feldspar intercepting the foliation of mylonite. The fluid might give rise to the strength reduction of the rock forming minerals and enhance the mylonization of the felsic veins. And the quartz-filling tensile fissures in the feldspar imply that hydra—fracture processes of water may have functioned. The mechanism of dynamic partial melting in the ductile shearing may be as follows:under the relative high stress. intensive shear heating caused the local increasement of rock temperature, which resulted in the melting of muscovite and amphibole firstly, sending out OH and forming solid-fluid two facies system . as a result-the shearing was greatly enchanced, then the fusion cooled and reerystallized. and finally formed the fetsic veins. Because the feedback nature of serf—organiztion characterizes this shear heating process. the felsic veins in the mylonite have rhythmic features. The conversion from contraction to extension of the crust in Southern Laoning during such a short interval(about 10～20Ma) may be explained by the constriction resulted in intensive shortening and thickening of the crust. which caused the unstability in gravity. The strong magmatism at the same time indicates the high initial temperature of the MOHO and high regional heat flux. Consequently. the unstability in gravity and thermal regime may cause the uplifting of the basement and hence regional extension in relatively short interva1.