Lateral variation of crustal structure and composition in the Cathaysia block of South China and its geodynamic implications

Abstract

In order to clarify lateral variations in the crustal structure and composition of the Cathaysia block in South China which was affected by violent Mesozoic and Cenozoic tectono-magmatic activities, we studied the crustal thickness and the Poisson’s ratio in this region using the H–κ stacking method of teleseismic receiver functions. Our results show that the Poisson’s ratio varies between 0.20 and 0.29 and the crustal thickness ranges from 26 to 34km in the Cathaysia block. The crustal thickness and Poisson’s ratio show considerable variations across the Lishui-Haifeng Fault. The Southeast Coast Magmatic Belt is characterized by Poisson’s ratios >0.25 and a crustal thickness of 28–33km, reflecting probably intermediate to mafic compositions of the crust. The southwestern part of the Cathaysia Fold Belt exhibits a crustal thickness of 27–30km and Poisson’s ratios <0.25, reflecting a more felsic crust. However, the northeastern part of the Cathaysia Fold Belt is characterized by an almost flat Moho at a depth of ∼31km and a strong variation of Poisson’s ratio from 0.22 to 0.27. Our results revealed an ESE-WNW trending boundary between the southwestern and northeastern parts of the Cathaysia Fold Belt, which is consistent with previous results of geochemical studies. The lateral variations in the crustal thickness and composition of the Cathaysia block may reflect not only the lithological variations of the crustal rocks but also significant effects of tectonism and magmatism on the interior of the Cathaysia block during the Mesozoic and Cenozoic.