A review of study on genesis of Paleoproterozoic graphite deposits in the North China Craton:Progresses and Questions
Three Paleoproterozoic graphite metallogenic belts have been identified within the North China Craton,including the Eastern Graphite Belt(Jiao-Liao-Ji orogenic belt),the Western Graphite Belt,and the Southern Graphite Belt.These graphite deposits account for 74％of the national reserves,and thus they are important sources of crystalline graphite deposits in China.On the basis of extensive collection and analysis of previous research results on graphite deposits in this area,this paper systematically summarizes the distribution,genetic mechanism and formation age of the Paleoproterozoic graphite deposits within the North China Craton,and its implications for the early environmental evolution of the Earth.The key problems are discussed and prospected.In the Eastern Graphite Belt,graphite ore bodies from the north to south are mainly produced in the Ji'an Group in the South Jilin,the Liaohe Group in the East Liaodong and the Jingshan Group in the North Jiaodong Peninsula.In the Western Graphite Belt,graphite deposits are mainly found in the Wulashan Group and the Jining Group.In the Southern Graphite Belt,graphite ore deposits are mainly exposed in the Taihua Group on the southern edge of the North China Craton.The graphite deposits in the three graphite metallogenic belts of the North China Craton have certain similarities,and they all belong to regional metamorphic graphite deposits.The ore-bearing rocks are metamorphic supracrustal rocks,including graphitic plagioclase gneiss,graphitic felsic gneiss,graphitic diopside granulite and graphitic marble.The form of graphite is mainly in the form of flake.Graphite carbon is mainly derived from organic matter,and there is a small amount of inorganic carbon mixed locally.The ore-bearing rocks in these three graphite metallogenic belts have similar sedimentary ages and metamorphic metallogenic ages.The sedimentary ages are roughly 2.0～2.2Ga,and the metamorphic metallogenic ages are about 1.8～1.95 Ga.The formation of these massive graphite deposits in the North China Craton is the most powerful evidence of the flourishing of life in the Paleoproterozoic,which has an important impact on the early environmental evolution of the Earth.On the one hand,the mass burial of organic matter can lead to the increase of atmospheric oxygen content and the positive shift of carbonate carbon isotope.On the other hand,these buried organic matter will undergo metamorphic decarbonization during the late subduction collision orogeny,consuming oxygen and release CO2 enriched with light carbon isotope 12 C,which may reduce atmospheric oxygen content and negatively shift carbonates carbon isotope value.However,the burial of huge amounts of organic matter in the Paleoproterozoic and the impact on the early atmosphere of the Earth in the later process of collision orogeny denudation weathering still need more geological data for quantitative estimation.These Paleoproterozoic graphite deposits formed in the North China Craton recorded the complete process of organic matter from burial to metamorphism to form graphite,which is an ideal object for studying these problems,and is of great significance to our understanding of the early environmental evolution of the Earth.
North China CratonPaleoproterozoicGraphite depositEarly Earth environmentGreat Oxidation event
万方数据
维普
