Abstract:
Linfen Basin is located in middle-southern part of the Fenwei Graben systems, North China Craton. As a late Cenozoic rift basin, it was defined by the northeast-striking and east-striking normal faults. Comprehensive constraints of sedimentary facies and provenance of the Chaizhuang section in the middle part of the basin indicating that the section can be divided into three units with different source areas, with some loess on the top of the section. This may provide important clues for exploring the tectonic setting of the basin evolution. Unit 1 in Pliocene (5~2.6 Ma) was deposited in alluvial fan and eolian environment with the nearby sedimentary rocks (i.e. limestone) to be the main source rocks. Unit 2 in the lower part of the Pleistocene (2.6~1.0 Ma) was deposited in a delta environment with mixed source rocks shed from Taihang Mountains and Zhongtiao Mountains on the eastern and southeastern of the basin, which include the Archean-Palaeoproterozoic granitic gneiss and gneiss, Neoproterozoic-Paleozoic carbonatite, Mesozoic terrigenous clastic rocks and some granitoids. Unit 3 in the upper part of the Pleistocene ( < 1.0 Ma) was deposited in a fluvial environment with the acidic magmatic rocks derived from the Taihang Mountains on the northeastern of the basin. Combined with the late Cenozoic regional regime evolution of the Shanxi Graben, we proposed that the northeast-striking normal faults were strongly active in Pliocene and influenced by the transtensional stress regime under NW-SE extension. The east-striking faults seem to be active in early Pleistocene (2.6~1.0 Ma) and were influenced by the NE-SW extension. From 1.0 Ma, the fluvial replaced the delta and lacustrine sedimentary environments. This indicates that the basin evolution is not as strong as in early Pleistocene which may be a result of the weakening of the extension. All these clues indicate that the main tectonic transition ages in Fenwei Graben systems influenced by the Xizang in Pliocene-Pleistocene may include Late Miocene-early Pliocene (5.0 Ma), 2.6 Ma and 1.0 Ma.