Comparative study of the Lanhualing Paleoproterozoic I−type granitoids and the Liaoji A−type granitoids in eastern Liaoning

Liaodong Peninsula is a significant component of the Jiao-Liao-Ji belt. It experienced complex process of structural evolution with the recorded effects of magma metamorphism in multiple periods. The 2.2 Ga Liaoji A-type granite and 1.89~1.85 Ga porphyritic granite/ syenite indicate the beginning and end of the effects of mountain formation in Paleoproterozoic respectively. The latest research shows that two unique types of granites have been formed under the effects of magmatism of 2.20~2.15 Ga. These two granites have different petrogenesis mechanisms and tectonic significance. In this paper, a detailed study of the Lanhualing granodiorite, Bailazi granodiorite and Huangpo diabase collected in the North of Qingchengzi lead-zinc concentrated area was conducted. The corresponding zircon U-Pb ages are 2177±19 Ma, 2129±36 Ma and 1876±29 Ma, respectively. The rock type and geochemical characteristics of the granodiorite show obviously differences from the typical 2.2 Ga Liao-ji A-type granites. It is characterized by weak peraluminous, low potassium calc-alkaline to alkaline, low content of Zr, Hf, Nb, Rb, low K₂O/Na₂O value, and extremely low content of total rare earth element. Therefore, it is categorized as typical I-type granite. According to the analysis of zircon Lu-Hf isotope, the value of ε_Hf (t) is −5.1~9.0. The age of the two-stage model(t_DM2) is in a range of 2089 Ma to 2817 Ma. The magma source consists of 2.5 Ga Archean crustal materials and a small amount of asthenospheric mantle materials. The granodiorite from Lanhualing area has the affinity geochemical property of island arcs or active continental margin. It may have been formed in the subduction and compression environment of arc magma; according to the A-type granite formed in extensional settings, we believe that the Paleoproterozoic belt of eastern Liaoning had experienced a tectonic environment of overall extension and local compression in the period of 2.2 Ga, which is the back-arc basin formed during or after the collision of the oceanic plate with the Longgang block.