3.3-3.1 Ga magmatism in the Dongshan Complex, Anshan area, Liaoning, China: Evidence from SHRIMP U-Pb zircon dating.

This paper reports SHRIMP U-Pb zircon ages of granitoids from the Dongshan Complex in the Anshan area, where there are Archean rocks with ages ranging from 3.8 to 2.5 Ga. A medium-coarse-grained trondhjemite sample has a 207Pb/206Pb weighted mean age of 3329 ± 22 Ma (MSWD=9.6) on magmatic zircons, with inherited zircons of 3687-3784 Ma. Magmatic zircons from fine-grained trondhjemite and adamellite samples have weighted mean 207Pb/206Pb ages of 3141 ± 8 Ma (MSWD=1.5) and 3142 ± 5 Ma (MSWD=0.35), respectively. The ~3.3 Ga medium-coarse grained trondhjemite was formed by anatexis of 3.8 Ga trondhjemiteic rocks. The 3.14 Ga fine-grained trondhjemite is considered to be a veinlet emanated from the nearby Lishan trondhjemite body with the same age. The 3.14 Ga adamellite cuts the fine-grained trondhjemite and is derived from continental material. Combined with early researches, it is indicated that ~3.3 Ga and ~3.1 Ga are two important crustal evolution stages in the Anshan area.