Abstract:

Through seismic section study and sedimentarytectonic analyzing, based on the volume of uplift and associated fault, the inversion structures in the Xihu Depression of East China Sea shelf basin are divided into four types: wide fold, narrow fold, wide fold with reverse fault, and narrow fold with reverse fault. The inversion structures in the Xihu Depression are characterized by the zonation from east to west and the partition from south to north. The Central Uplift Belt has the strongest inversion structure, the East Marginal Belt is relatively gentle and the inversion in the West Marginal Belt is the weakest. The North Block comprises a lot narrow folds, while the Middle Block comprises strong inversion generally but weak in some places, The South Block have the opposite regulation to Middle Block. The inversion structures in the study area are mostly folds and supplemented with different degree of faults, so three parameters that are reverse displacement of inversion fault, amplitude of inversion fold and compression ratio in the Central Uplift Belt are chosen to quantitatively study the inversion characteristics in the Central Uplift Belt. The result shows that the inversion structure in the North Central Uplift Belt is strong, but limited; while the inversion structure in the Middle Central Uplift Belt is very strong or weak; the South Central Uplift Belt comprises strong inversion in some places, but weak mostly. The inversion structures in the Xihu Depression were caused by Longjing tectonic movement in the middlelate Miocene. The inversion faults were evolved by the reversal reactivation of preexisting normal fault; the reverse displacement generally reduced from bottom to the top. Inversion folds are more likely to develop on the top strata; it generally enhanced from bottom to the top. The subduction of Philippine Sea Plate to Asian Plate, caused Okinawa Trough to open, which caused the west boundary of Okinawa Trough to be pushed toward west. This push made the inversion structures in the Xihu Depression formed.

Key words: Xihu Depression, inversion structure, tectonic analysis, inversion parameter, dynamic background of inversion