Research On Geochronology And Metamorphism Of Khondalite-Series Rocks Of The Jining In The North China Craton

Jining region includes Jining and its neighbour regions such as Zhuozi, Liangcheng, Badi, Xinghe, Tuguiwula etc., and the research area locates in the junction of central belt and the eastern khondalite belt in the west of North China Craton. This paper carry out a research on Geochronology and Petrology of khondalite-series rocks of the Jining region, and the main achievements gained as follows:The main mineral assemblage of khondalite-series rocks in the preliminary stage is kyanite-plagioclase-biotite-garnet-quartz; the abundant sillimanite develops with progression of metamorphic reaction so that forming the assemblage of garnet-sillimanite-biotite-k-feldspar-plagioclase-quartz. Cordierite is found in the late retrometamorphism stage. This paper mainly consider five types of Khondalite rocks:(Biotite) sillimanite-garnet cordierite leptynite gneiss; Spl-Sil-Ksp-Grt-Bt vein; Granite; Sillimanite-garnet K-feldspar mylonite; (Cordierite) sillimanite-garnet gneiss.Jining khondalite metasedimentary rocks, i.e. Sil-Bt-Grt leptynite gneiss, contain oldest U-Pb age at 2550-2480 Ma, suggesting a late Achaean/early Palaeoproterozoic detrital source. The depositional age could be defined by concordant ages 2228-2027 Ma of zircons in the Sil-Bt-Grt leptynite gneiss and cordierite-bearing sillimanite-garnet two-feldspar gneiss, which shows that the sedimentary age of Jining khondalite sediments must more than 2.0 Ga. And the belt of khondalite-series rocks is formed by the collision between the north Yinshan and the south Ordos terranes before final amalgamation of the NCC basement.Before formation of the khondalite Belt in the central North China, there still existed an ocean between the Eastern and Western blocks of the NCC. This ocean disappeared beneath the orogenic khondalite rocks when convergence between the two blocks occurred. Continued compression between the two blocks resulted in gneiss to granulite-facies metamorphism of khondalite-series rocks. The final suturing of the Eastern and Western blocks occurred at 1.85 Ga, resulting in the formation of the Trans-North China Orogen.