Difference in U-Pb isotope ages between baddeleyite and zircon in metagabbro from the Fushui complex in the Shangnan-Xixia area,Qinling orogen

There are relatively coarse-grained baddeleyite and zircon with higher U and Pb contents in metagabbro from the Fushui complex in the Qinling orogen. They are very good minerals for U-Pb isotope dating. Baddeleyite and zircon from medium- and coarse-grained hornblende-biotite gabbro yielded SHRIMP and TIMS U-Pb ages of 501.4±1.2 Ma and 480.0±3.4 Ma respectively. The age difference between the two minerals is about 20 Ma. The transformation of some baddeleyite to zircon in the rock and zircon genesis were studied. The study shows that the baddeleyite age of 501.4±1.2 Ma should be interpreted as the formation age of intermediate-basic rocks in the Fushui complex of the Qinling orogen. However, the genesis of zircon and the change of its U-Pb isotope system is relatively complex in the process of metamorphism, so the rational interpretation of the geological implication of its age (480.0±3.4 Ma) needs more studies.