Depositional age, provenance and tectonic setting of the Proterozoic Ruyang Group, southern margin of the North China Craton

Abstract

Late Paleoproterozoic rifting and accompanying magmatism and sedimentation, which occurred widely in the North China Craton, are interpreted to be related to the breakup of the supercontinent Columbia. The Ruyang Group, overlying the Xiong’er Group in the southern margin of the craton, is a typical fluvial-marine sedimentary sequence mainly composed of sandstone with minor shale and dolostone. Sandstones from the Ruyang Group exhibit high contents of SiO2 (86.8–98.7wt.%) but relatively low contents of Al2O3, K2O, Na2O, TiO2 and MgO, typical of mature siliceous clastic rocks. Trace elements of these rocks indicate that the sequence was deposited in a passive continental margin environment and that the sedimentary detritus was derived from a Paleoproterozoic silicic-intermediate source, similar to other Paleo-Mesoproterozoic sedimentary sequences in the region.Detrital zircons from three sandstone samples of the Ruyang Group yield 207Pb/206Pb ages ranging from 1.70Ga to 2.70Ga with two pronounced peaks at ca. 2.10Ga and 1.86Ga. A weighted mean age at 1744±22Ma from nine young zircon ages between 1.80Ga and 1.70Ga can constrain the maximum depositional age of the Ruyang Group. Most detrital zircons exhibit negative ɛHf(t) values ranging from −15.6 to 0 and old TDMC ages ranging from 2.50Ga to 3.60Ga, implying reworking of Archean crust. A close match between the U–Pb ages and TDMC(Hf) ages, as well as the positive ɛHf(t) values for some detrital zircons, indicate a contribution of juvenile materials. The detrital zircon grains have TDMC(Hf) ages clustering between 3.00Ga and 2.60Ga with a peak at around 2.80–2.70Ga, indicating a major period of crustal growth at this time.