Genesis and Tectonic Significance of Miocene Tephrite in Laohushan Volcanic Area,Jilin Province
The Laohushan monogenic volcano is located in Dakouqin area,southern Jilin Province.In order to explore the geochemistry characteristics and genesis of the Miocene tephrite in this volcanic area,together with the coupling between it and the evolution of regional fault structure,the whole rock geochemistry and Pb isotope study on it were carried out.Na2O/K2O values of the tephrites are range from 1.30 to 1.38,with low A/CNK(0.97-1.09)and high Mg#(58.05-61.11)values.The tephrites are enriched in high field strength elements(HFSEs),such as Th,U and Nb,and relatively weakly enriched in large ion lithophile elements(LILEs),such as Rb,Ba and K,with LREE/HREE=10.66-11.32.The values of 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb are range from 17.661 to 17.675,15.451 to 15.457 and 37.652 to 37.692,respectively.The parental magma is mainly from the asthenosphere mantle,with a small amount of subducted oceanic crust components,which shows the attribute characteristics of OIB(oceanic island basalt)or intraplate metasomatic enriched mantle source.The depth range of magma formation is about 93-105 km,and the existence of the Yitong-Shulan fault provides conduit and space for magma upwelling and fissure eruption.In addition,the formation of basaltic magma and its associated volcanic activity occurred in an extensional tectonic environment.
element geochemistrylead isotopetephriteLaohushan volcanoJilin Provincegeochemistrypetrology
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