| Abstract:Archean supracrustal rocks in western Shandong include two stages of supracrustal rocks in the early Neoarchean and the late Neoarchean. The early supracrustal rocks are mainly composed of metamorphic basalt-Komatiite, and the late supracrustal rocks are mainly composed of metamorphic volcanic rocks-clastic sedimentary rocks and BIF. The Hanwang iron deposit is located in the northwest of western Shandong. There are a large number of meta-basalt-Komatiite in the iron ore area. It is believed that the BIF was formed in the early Neoarchean, while the new study suggests that the BIF in western Shandong area was formed in the late Neoarchean. In this paper, the zircon SHRIMP U-Pb dating of the biotite granulite interbedded with BIF and the gneissic granodiorite intruded in the Hanwang iron ore area was carried out, and the ages were 2529 ± 7 Ma and 2534 ±11 Ma, respectively. The TREE, (La/Yb) n and Eu/Eu* of biotite granulite and gneissic granodiorite are76?10-6,19.8,0.84 and 82.7?10-6,17.3,1.14, respectively. The εHf values and single-stage Hf isotopic model ages of their magmatic zircons are 5.5-9.46 Ga, 2.5-2.6 Ga and 6.3-9.4 Ga, 2.48-2.60 Ga, respectively. The study supports the recognition that BIF in western Shandong was formed in the late Neoarchean. The formation of supracrustal rocks, metamorphic deformation and granodiorite intrusion occurred in a very short time range. The study also shows that the protolith of the biotite granulite is dacitic volcanic rock, which is likely to be formed by the strong crystallization differentiation of the newborn basaltic magma. The granodiorite was formed by the partial melting of the newborn basaltic rock, and the continental crust material was added during the formation process. |
