The Age and Geological Significance of Early Neoproterozoic Mafic Sills on the Eastern Margin of the North China Craton:Evidence from Zirconology
The tectonic setting of the Neoproterozoic mafic sills (dykes) in the eastern margin of the North China Craton is of great significance for reconstructing the position of the Craton in Rodinia supercontinent. By analyzing the structure,paragenetic relationship with other minerals,and trace element characteristics of zircons in four mafic rock sill samples from Dalian and Xuzhou regions,it is found that they have typical structural and trace element characteristics of mafic magmatic zircons. Most of the crystallization temperatures (about 800-900℃) are consistent with those of zircons in mid-ocean ridge basalts,and some zircons can be observed to appear in clinopyroxene as inclusions. The above characteristics indicate that these zircons were formed in the early stage of cooling crystallization of mafic magma. Their U-Pb ages (881 Ma,876 Ma,914 Ma,and 925 Ma) can represent the emplacement age of mafic sills,and their trace elements show the characteristics of continental island arc magmatic zircons. Based on the geometric distribution of mafic sills (dykes) and the duration of magmatic activity,we suggest that they may have formed in a subduction related tensile environment.
mafic sillNeoproterozoicNorth China Cratonzirconologygeochronologymineralogy
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