| Abstract: | ![]()
The internal structures of zircons in eclogite from Huangzhen have been studied by cathodoluminescence(CL) microscopy. Two growth stages were distinguished:protolith magmatic cores and metamorphic overgrowthrims. These different domains were analyzed for trace ele-ments using LAM-ICP-MS. The protolith and theovergrowth zircons have different trace elements charac-teristics. The trace element contents of protolith zircons arehigh and very variable. The overgrowth zircons show a typi-cal trace element feature of equilibrium with garnet, e.g. lowcontents of HREE (132.2-197.6 ?g/g) and small differentialdegree of HREE ((Yb/Gd)CN=8.6-11.9). The contents of Nb,Ta and the ratio of Nb/Ta are lower in the metamorphic do-mains (0.5-1.4 ?g/g, 0.7-1.5 ?g/g, 0.3-1.3, respectively)than in the protolith domains (3.8-19.7 ?g/g, 2.7-12.1 ?g/g,1.0-4.6, respectively). This is the first time to give the evi-dence that the metamorphic zircon equilibrates with therutile, which formed during the peak metamorphic stage.The REEs and other trace elements data demonstrate that the metamorphic zircons overgrow in the eclogite-facies con-ditions. The trace element composition of zircon can there-fore give new ways to constrain their formation conditions. |
