Abstract:We found Late Carboniferous tonalites in the south of Hongshishan SSZ- type ophiolitic melange. This paper discuss their geological characteristics, genesis and tectonic environment, combining with the relationship between spatiotemporal distribution and evolution of Late Paleozoic SSZ ophiolite, island- arc magmatic rocks in Hongshishan—Baiheshan suture zone. We summarize regional tectonic evolution, so as to provide some chronological constraints for subduction, extinction of Hongshishan ocean and continental crust accretion process. Methods: Based on field geological survey, petrology, geochemistry and LA- ICP- MS zircon U- Pb geochronology of the tonalites in the south of Hongshishan, this paper discusses the petrogenesis and tectonic setting of the tonalites, and the final closure time and subduction process of the Hongshishan Ocean. Results: The tonalites in the south of Hongshishan are characterized by high silicon w(SiO2)=63. 95%~66. 22%, rich aluminum w(Al2O3)=15. 31%~16. 61%, rich sodium and poor potassium, A/CNK=0. 98~1. 45. Zircon U- Pb dating shows that the tonalites in the south of Hongshishan were emplaced in Late Carboniferous, with age of 306. 9~309. 9 Ma, in the northern Beishan orogenic belt, which is the Late Carboniferous. Conclusions: The contents of Zr, Nb, Ce and Zr+Nb+Ce+Y of the rock samples in this paper are all lower than the lower limit of A- type granite, and the samples fall into the area of undifferentiated granite in the discriminant diagram of granitoid genetic type and show the characteristics of I- type granite. The rocks are enriched in Rb, Ba, Th and La, and depleted in high field strength elements such as Nb, Ta, P, Ti and Eu. In terms of chemical composition, the values of Mg# are relatively low (0. 42 ~ 0. 52), and the degrees of differentiation are relatively low (D.I.=64. 5 ~ 73. 5). They were formed in the island arc environment during the oceanic crust subduction period.