| The geological evolution of the South Dabie zone(SDZ), especially exhumation history, is still unclear. This thesis reports the secondary ion mass spectrometry(SIMS) U–Pb dating results of zircons and rutiles and trace element analyses of zircons from the SD eclogites in the Huangzhen and Zhujiachong areas and migmatited eclogites in the Hualiangting Reservior, with the aim of constraining tectonic evolution of the SDZ. The dating results indicate that two groups of ages are determined, 740-780 Ma and ~220 Ma, respectively. The former corresponds to ages of the Neoproterozoic protoliths from which zircons display oscillatory zoning and resorption structures in CL images, have high Th/U ratios(>0.4), and show steep heavy rare earth element(HREE) patterns. The latter is consistent with timing of eclogite facies metamorphism. The Triassic zircons from the eclogites have low Th/U ratios and show flat HREE patterns. Zircons from the migmatited eclogite display both flat and steep HREE patterns and yield ages of 219 ± 2 Ma, implying that migmatization timing is similar to the timing of eclogite facies metamorphism. SIMS U-Pb dating results of rutiles from these samples yield identical lower intercept ages ranging from 197 ± 4 to 197 ± 5 Ma, which reflects a cooling history of the SDZ at ~ 500 ℃. The SIMS U-Pb dating result of zircons from the Beiyu area within the Susong zone is 221 ± 4 Ma, representing peak metamorphic timing of the Susong zone. Compared with the researches of the Central Dabie zone(CDZ), the U-Pb dating results in this study show that the SDZ just experienced eclogite facies metamorphism when the CDZ exhumated rapidly to the depth with the temperature below ca. 500 ℃. Until about ~200 Ma the SDZ just exhumated to the depth with the temperature below ca. 500 ℃. These lines of evidences indicate that the subduction and exhumation histories are significantly different between different slices. |
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