Detrital zircon U-Pb, Hf isotopes, detrital rutile and whole-rock geochemistry of the Huade Group on the northern margin of the North China Craton: Implications on the breakup of the Columbia supercontinent

摘要

Supracrustal successions in the Zhaertai-Bayan Obo-Huade rift zone on the northern margin of the North China Craton include the Zhaertai, Bayan Obo and Huade Groups from west to east. The Huade Group, which has been subdivided into four formations, is composed of basal pebbled quartzites, quartzites, schists, phyllites, marbles, slates and diopsidites. Geochemistry of the metasedimentary succession indicates that source rocks of the lower two formations are felsic, displaying passive margin signatures, whereas those of the upper two formations have continental island arc or active continental margin signatures. U-Pb ages of detrital zircons from the group yielded three age populations of 2690-2450, 2150-1710 and 1660-1330 Ma, of which the youngest age population only exist in the upper Huade Group. The dominant 2690-2450 detrital zircons were likely sourced from the granitic rocks in the Yinshan Block. The subordinate 2150-1710 Ma detrital zircons were probably recycled from the metasedimentary units from the Khondalite Belt and/or derived from the similar aged granitic plutons of the Hongqiyingzi "Group", which are also evidenced by the similar geochemical features of rutiles from the Huade Group and the Khondalite Belt. Minor amounts of 1660-1330 Ma detrital zircons may have derived from the North American and/or Baltica cratons connected to the northern margin of the North China Craton in the Columbia supercontinent. The youngest detrital zircon age peak of ~1337 Ma in the upper Huade Group suggests that the sedimentation began after ~1.34Ga. In combination with the ~1320Ma granitoids cross-cutting it, depositional ages of the upper Huade Group can be constrained between ~1.34 and ~1.32 Ga. Taking into account the lithostratigraphic features, provenances and depositional ages, a continental rift basin deposit represented by the upper Huade Group on the northern margin of the North China Craton developed between ~1.34 and ~1.32 Ga, which indicates that the final breakup of the North China Craton from the Columbia supercontinent happened in the middle Mesoproterozoic.