Detrital zircon U-Pb and Hf isotopic and whole-rock geochemical study of the Bayan Obo Group, northern margin of the North China Craton: Implications for Rodinia reconstruction

Abstract

The Zha’ertai-Bayan Obo-Huade rift zone is located in the northern margin of the North China Craton (NCC), where rift-related supracrustal successions are divided into the Langshan, Zha’ertai, Bayan Obo and Huade groups from west to east. The Bayan Obo Group unconformably overlies the Late Neoarchean to Paleoproterozoic basement rocks and has been subdivided into three successions by two prominent unconformities. Depositional ages of the lower, middle and upper succession can be constrained in the period of 1.81–1.65Ga, 1.56–1.35Ga and 1.19–0.92Ga respectively based on ages of the youngest detrital zircons and latter intrusions. Geochemistry of the meta-sedimentary samples suggest that most of them were directly sourced from intermediate to felsic magmatic and metamorphic rocks and only the Halahuogete samples from the middle succession display reworking features. U-Pb ages of detrital zircons from the group yielded age peaks of 2.52–2.48Ga, 1.95–1.85Ga, 1.74–1.61Ga, 1.55–1.53Ga, 1.37–1.34Ga and 1.18–1.13Ga. The late Neoarchean to middle Paleoproterozoic detrital zircons are documented in the lower and middle successions and are derived from the ca. 2.5Ga Guyang and Xi Ulanbulang areas and ca.1.9Ga Halaqin and Liangcheng areas in the Yinshan Block. The late Paleoproterozoic detrital zircons with low εHf(t) values from the Bilute Formation are interpreted to be sourced from the coeval rift-related granitic plutons and volcanic rocks in the northern NCC. On the other way, detrital zircon age patterns of the late Mesoproterozoic to early Neoproterozoic sedimentary units at the northern and southeastern margins of the NCC are similar with those from the western and northern margin of the Fennoscandian shield. Combined with recent paleomagnetic and geological data, we infer that the NCC and Baltica have not separated until 0.89Ga in the Rodinia supercontinent.