Provenance and tectonic setting of the Statherian Hangaoshan Group: Implications for evolution of the North China Craton during late Paleoproterozoic

Abstract

The Hangaoshan Group, mainly composed of siliciclastic rocks, is one of the best-preserved sedimentary units exposed in the central North China Craton (NCC) from the Statherian Period. The Hangaoshan Group overlies the Paleoproterozoic Jiehekou Group and underlies Cambrian strata, with both contacts representing unconformities. Detrital zircon U-Pb dating and regional stratigraphic correlation constrain the depositional age of the Hangaoshan Group during ca. 1.8–1.69 Ga. High CIA (>62), low ICV (mostly 0.25–1.12) values and high SiO2/Al2O3 (2.5–22.2) ratios are suggestive of mature sources that experienced moderate to intensive chemical weathering. Low textural and compositional maturity indicate that the provenance of the Hangaoshan Group is mainly proximal deposition. Large proportion of quartz grains, light REEs enrichment relative to heavy REEs ((La/Yb)N = 4.37–33.7), negative Eu anomalies (δEu = 0.41–0.79), high Th/Co (0.44–20.5), high La/Sc (1.35–17.2) ratios, low La/Th (0.99–9.64) ratio and low Hf content (1.34–24.5) suggest that the provenances are mainly composed of felsic magmatic rocks with minor contributions from intermediate-basic meta-volcanic rocks, which is also supported by the A-CN-K, Al2O3-Fe2O3T*2-MgO*2 and Co-Nb-Y diagram. Detrital zircon ages from the Hangaoshan Group are mostly between 2.26 Ga and 1.84 Ga with a notable peak at 2.18 Ga and two subordinate peaks at 2.08 Ga and 1.98 Ga. Geochronological and isotopic similarity suggests that the Chijianling-Guandishan TTG and the Jiehekou Group in the Lvliang area are the dominant sources for the Hangaoshan Group, while the Yejishan Group, 2.2 Ga mafic meta-volcanic rocks, and Huijiazhuang and Xiyupi granite also contributed to lesser degrees. In terms of petrological characteristics, most gravels in the lower conglomerate of the 3rd Formation (Fm) are sandstone fragments of the 1st and 2nd Fm, suggesting that the 3rd Fm is mainly derived from the older diagenetic rocks of the Hangaoshan Group, with a lesser amount of basement rocks. Generally, the Hangaoshan Group was likely deposited in a rift basin. In combination with previous studies on other late Paleoproterozoic volcanic-sedimentary sequences, we consider that the Xiong’er rift in southern NCC extended into the midcontinent at the Lvliang area during ca.1.78 Ga and then the continental crust was uplifted in the Lvliang area during the Mesoproterozoic–Neoproterozoic.