Isotopic age of zircon of the Dongshan metamorphic rocks in Fujian Province and its geological significance

LA- ICP-MS zircon U- Pb dating was carried out for Dongshan metamorphic rocks in Fujian Province. Their ages obtained are 176.8 Ma, 203 Ma, 230 Ma,1320 Ma and 1810 Ma respectively, Among them, the 176.8 Ma is the age of magmatic zircon in volcanic-sedimentary rocks, representing the formation age of the sedimentary rock; 203 Ma and 230 Ma represent Late Triassic granitoids; 1320 Ma and 1810 Ma represent the metamorphic basement age of metamorphic rocks. The geochemical data indicate that these metamorphic rocks have poor Si and high Al, Fe, K and are characterized by low Co,Ni,V content and high Ba, Rb, Zr, Hf, U, Th, La values,exhibiting crust source features; relatively high REE content, slight enrichment of LREE, indistinct fractionation between LREE and HREE, and weak negative Eu anomaly all indicate that sources of the metamorphic rocks might have been mantle-crust and granitoids of I series. The Qingyingshan Formation seems to have been the early Jurassic product of the marine-terrigenous facies at the rifting stage, accompanied by volcanism.