LAUSR

ABSTRACT Whether the North Qinling Terrane (NQT) was accreted to the North China Craton (NCC) in the Proterozoic is still a matter of debate. We report the first detrital zircon study from the Baishugou Formation, which forms the uppermost part of the Mesoproterozoic Guandaokou Group, at the southernmost NCC margin. Detrital zircons from carbonaceous silty phyllite in the lower part of the Baishugou Formation yield U–Pb ages peaking at ca. 2500 Ma, with minor peaks at ca. 2300–2000, 1800, and 1600 Ma, and εHf(t) values ranging from −10.8 to +9.1. These zircons are considered to have been sourced from the NCC. In contrast, the middle-to-upper part of the formation contains detrital zircons which yield an age group ranging from 1800 to 1000 Ma, with peaks at 1800, 1500, 1300, and 1100 Ma; the zircons with ages of 1500–1300 Ma dominantly have εHf(t) values greater than +5 and the majority plot along the depleted mantle evolution curve. The striking difference between the U–Pb ages of the detrital zircons from the upper and lower parts of the formation suggests a shift in provenance. Magmatism at 1500–1300 Ma has not been reported from the southern margin of the NCC but has been discovered in the NQT. Hence, we deduce that the zircons from the upper part of the formation were primarily derived from the NQT, where an episode of crustal growth and magmatism is recorded between 1500 and 1100 million years. The variable sediment provenances imply that the NCC and NQT could be connected during the late Mesoproterozoic to early Neoproterozoic. The pattern of detrital zircon ages in the new sediments from the Baishugou Formation is distinct from those in the Kuanping Group and the Palaeozoic Erlangping Complex, which are at present sandwiched between the NCC and the NQT. The detrital zircons from these two groups are dominated by an age peak at ca. 1000 Ma, which is formed as the result of amalgamation of the NQT and the Rodinia Supercontinent during the Grenville orogeny. It is possible that the new sediments of the Baishugou Formation were deposited before Grenville orogeny.