Oil & Gas Geology ›› 2014, Vol. 35 ›› Issue (5): 742-748.doi: 10.11743/ogg20140520

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Zircon U-Pb age and formation model of volcanic rocks from Nanpu Sag of Bohai Bay Basin

Du Jingxia, Shi Wenwu, Zhou He, Wang Quanli, Xia Qiujun, Liu Junrong   

  1. Research Institute of Exploration & Development, PetroChina Jidong Oilfield Company, Tangshan, Heibei 063004, China
  • Received:2014-02-10 Revised:2014-06-20 Online:2014-10-08 Published:2014-10-17

Abstract: Nanpu Sag underwent two magmatic cycles and four episodic eruptions.Zircons of volcanic rocks from Nanpu Sag are dated by U-Pb SHRIMP,LA-ICPMS and Lu-Hf isotope method.The results indicate that more than 95% of zircons in the early magmatic cycle are formed by metamorphic recrystallization,with a big range of U-Pb age.It is explained that they are formed by collision granite crust in 1 800 Ma,which is caused by remelt and recycling process induced by collision between new crust of Middle and Neo-Archean(2 900~2 600 Ma)with palaeo-oceanic crust.In the middle to late magmatic cycle,zircons are formed by crystallization of mantle-derived magma overflow,and they contain magmatic zircon and rich captive crystal,which are helpful for chronology and isotope studies.Through those zircon ages,a vertical sequence of correspondent tectono-thermal events of the North China craton and Nanpu Sag is established.Moreover,the absolute ages of mantle-derived magma overflow and the related strata are calibrated accurately.The result shows that Guantao Formation belongs to Miocene,Dongying Formation belongs to the Oligocene and Shahejie Formation crosses Paleocene and Eocene.

Key words: Cenozoic basalt, Zircon U-Pb age, volcanic rock, Nanpu Sag, Bohai Bay Basin

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