Multi-stage Mafic Magmatism Along The Northern Margin Of The North China Craton And Their Geological Implications

The North China Craton is one of the oldest craton on Earth.Pre-early Paleozoic mafic dyke swarms widely occur along the northern margin of the North China Craton.The study of the type and spatio-temporal relationship of the mafic dyke swarms allows us to better understand their tectonic settings,the evolution of mantle source area and the roles of the supercontinental reconstruction.This study reports two periods new mafic dykes in the Fengzhen area,yields the zircon U-Pb LA-ICP-MS ages of 1806 ± 13 Ma and 437.2 ± 5.3 Ma,respectively.Combined with previous published data,this effort reveals five stages of mafic magmatism as follows :(1)at ca.1.8 Ga metamorphic mafic intrusions;(2)at ca.1.78-1.73 Ga mafic dyke swarms;(3)at 1.68-1.67 Ga Gabbro plutons and mafic dykes;(4)at ca.1.32 Ga mafic sill swarms and Gabbro plutons;(5)at ca.1.23 Ga mafic dyke swarms;(6)at ca.925 Ma mafic dyke swarms;(7)at ca.437 Ma mafic dykes.The tectonic settings and magmatic evolution are discussed in this study by using geochemistry data,and the further discussion on the tectonic evolution of the northern margin of the North China Craton.The northern margin of the North China Craton occurred an orogenic event at ca.1.9 Ga,and then an post-orogenic extension event in the North China craton started at ca.1.8 Ga.The tectonic setting of northern margin of the North China Craton transform into the continental breakup setting at ca.1.78 Ga and two main rift belts are developed.Three different types mafic magmatism were presented at 1.78-1.73 Ga,1.68-1.67 Ga and 1.32-1.23 Ga,respectively.which are interpreted as the different phases of within the rift evolution process.Also,it was related to the breakup process of the Columbia Supercontinent.After that,the northern margin of the North China Craton went through the Grenville orogeny,the North China Craton is as to a part of the Rodinia Supercontinent.Rodinia Supercontinent is suggested to breakup since ca.925 Ma,and the northern margin of the North China Craton is interpreted as the passive continental margin.At ca.500 Ma,the northern margin of the North China Craton changes from passive continental margin to activecontinental margin because the Paleo-Asian oceanic crust subducted beneath the North China Craton.At the same time,the Bainaimiao island arc were developed during the subduction process.The southward subduction process finished at ca.437 Ma,and a back-arc basin was developed between the Bainaimiao island arc belt and the North China Craton as the evidence of the mafic dykes within the North China Craton.