Geochronlogy and Geological Event Sequences of Hengshan-Wutai Precambrian Complex
NIU Xianglong LI Jianghai (Key lab of orogenic belt and crustal evolution, School of earth and space sciences, Peking University, Beijing, 100871)
Large amount of isotopic age data achieved in recent 10 years in Hengshan Wutai Mt. show that the climax value of Hengshan complex`s (2520 Ma) is 20Ma less than Wutai complex`s (2540 Ma), which coincides with the opinion of Hengshan complex being the arc root of Wutai arc. Based on the comprehensive analysis of the various geological records, three evolution stages have been suggested, 2.70-2.60 Ga, the formation stage of the primary crust in Hengshan Wutai areas, 2.60-2.52 Ga (not less than 2.45 Ga), the subduction and collision stage from the East to West Block and 2.50-1.75 Ga, the evolution stage of the early overlying strata. The last one is subvided five periods, which are: 1) 2.50-2.30 Ga, the continental plateau basalt eruption period; 2) 2.30-2.20 Ga, the stable subsidence period; 3) 2.20- 2.10 Ga, the tectonic activation and the emplacement of anorgenic granite period; 4) 2.10-1.85 Ga, the mantle plume activition period? 5) 1.86-1.75 Ga, the emplacement of large scale basic dyke swarms and the decomposition of North China Craton (NCC) period.