Abstract
The Anshan area in the northeastern part of the North China Craton contains the oldest known rocks in China. Rocks with ages of ∼3.8 Ga are present in three trondhjemite-dominated gneiss complexes, referred to as the Baijiafen, Dongshan and Shengoushi complexes. The oldest material identified in these complexes has weighted mean 207Pb/206Pb ages of 3800 ± 5 Ma, 3794 ± 4 Ma and 3777 ± 13 Ma, respectively. In addition, younger geological events at 3680 ± 19 Ma, 3620 ± 23 Ma, and 3573 ± 21 Ma have been identified, recording the emplacement of several generations of trondhjemite. A biotite schist of possible supracrustal origin contains a zircon population with a weighted mean 207Pb/206Pb age of 3723 ± 17 Ma and is cut by a 3620 Ma trondhjemite, implying formation prior to ∼3.62 Ga. TDM(Hf) model ages for the zircons range from 3256 to 4264 Ma, but are mostly ∼3.9 Ga, indicating that significantly older crust was not present in the source region of the trondhjemitic magmas.
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