关键词: 吉林南部, 蚂蚁河岩体, 锆石U-Pb年代学, 地球化学

Abstract: The Mayihe pluton, located in southern Jilin Province, consists mainly of gabbro-diorite, granidiorite, and monzogranite. Such characteristics of zircons from gabbro-diorite and monzogranite imply their magmatic origin, as euhedral shape, typical oscillatory zoning and high Th/U ratios (0.14-2.56) . LA-ICP-MS zircon U-Pb dating indicates that the ²⁰⁶Pb/²³⁸U ages of zircons from gabbrodiorite range from 219 to 227 Ma, yielding a weighted mean age of (224±4) Ma (n=8), and those of zircons from monzogranite from 217 to 241 Ma, yielding a weighted mean age of (226±3) Ma (n=19). The petrogeochemistry of Mayihe pluton shows its bimodal rock association. Gabbrodiorites are characterized by lower content of SiO₂, higher content of TiO₂, MgO and CaO. Moreover, they are rich in both large ion lithophile elements (LILEs) and light rareearth elements (LREEs), depleted in high field strength elements (HFSEs). Their initial ⁸⁷Sr/⁸⁶Sr ratios and ε_Nd(t) values are 0.703 7 and 3.45 to 3.82, respectively, suggesting a depleted lithospheric mantle source. In contrast, grandiorites and monzogranites have higher SiO₂ and lower TiO₂, MgO and CaO. They are strongly rich in Rb, Th, U, and depleted in Nb, Ta, P, Ti, Ba, Sr. Their initial ⁸⁷Sr/⁸⁶Sr ratios and ε_Nd(t) values range from 0.705 3 to 0.705 8 and from -0.73 to -3.40, respectively. Characteristics above suggest that both grandiorite and monzogranite be derived from the partial melting of the lower continental crust. The bimodal rock association of the Mayihe pluton，together with the research on regional tectonics, demonstrates that the pluton were resulted from the post-collision extensional environment between the North China craton and Yangtse craton. It can be concluded that thinning or destruction of the lithosphere in the North China craton could be initiated in the Late Triassic, and the southern Jilin Province belongs to this lithosphere-thinning region.

Key words: southern Jilin Province, Mayihe pluton, zircon U-Pb geochronology, geochemistry