福建东山变质岩LA-ICP-MS同位素年龄及其地质意义

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

LA-ICPMS锆石U-Pb法测得东山地区变质岩的年龄为176.8 Ma、203 Ma、230 Ma、1320 Ma、1810 Ma等,其中176.8 Ma为火山-沉积岩中的岩浆锆石,代表着地层形成的年龄;203 Ma、230 Ma为继承岩浆碎屑锆石,代表了晚三叠世源区火成岩的物源年龄;1810 Ma、1320 Ma为变质岩继承锆石,代表了基底物源年龄。地球化学分析结果表明:岩石具贫硅、高铝、铁,富钾,Co、Ni、V含量低,Ba、Rb、Zr、Hf、U、Th及La含量高,具壳源特征;稀土元素总量较高,轻稀土略富集,轻、重稀土元素分异不明显,无明显的负铕异常,表明变质岩的部分物质与地幔有关。福建东山地区亲营山组可能属早侏罗世晚期华夏陆块边缘进入裂陷期海陆交互相火山-沉积的产物。

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.