The paper reports SHRIMP U-Pb zircon data of a dark eclogite and a post-eclogite garnet-bearing gneissic granitic rock from the Bixiling area, Yuexi County, Anhui Province, in the eastern Dabie Mountains. The eclogite...The paper reports SHRIMP U-Pb zircon data of a dark eclogite and a post-eclogite garnet-bearing gneissic granitic rock from the Bixiling area, Yuexi County, Anhui Province, in the eastern Dabie Mountains. The eclogite, which is metamorphosed basic tuff, contains very scarce zircons in omphacite or garnet, but more zircons in quartz. They usually exhibit a double-layered texture, as shown clearly in cathodoluminescence images. Their inner main parts give a 206Pb/238U age of 757±7 Ma, representing the approximate age of the high-pressure (HP)- ultrahigh-pressure (UHP) metamorphic event during which the eclogite was formed. The outer peripheral parts of the zircons, which have been modified by late-stage fluids, give an age of 223±3 Ma. The granitic rock contains more zircons of anatectic origin found mostly in feldspar and quartz and usually also showing a similar composite texture. The inner main parts of the anatectic zircons with oscillatory zoning give a 206Pb/238U age of 727±15 Ma for the approximate age of the emplacement of the granitic rock, and their outer parts, an age of 219±3 Ma for a similar or even the same fluid event. It is thus suggested that the HP-UHP metamorphism of the Bixiling eclogite facies rocks took place during the Neoproterozoic Jinningian, and the Indosinian age values may only represent a late event in the nature of fluid activity.展开更多
U-Pb zircon dating on two foliated garnet-bearing granite samples in the western Dabie ultra-high-pressure (UHP) metamorphic unit yields concordant ages of (234±4) Ma and (227±5) Ma, respectively. These ages...U-Pb zircon dating on two foliated garnet-bearing granite samples in the western Dabie ultra-high-pressure (UHP) metamorphic unit yields concordant ages of (234±4) Ma and (227±5) Ma, respectively. These ages, following the UHP peak metamorphism, represent the magma emplacement ages for the foliated garnet-bearing granites. This, for the first time, shows that there are the Triassic granites in the Dabie Mountains. The foliated garnet-bearing granites resemble A-type granite in geochemical characteristics, indicating that they were formed in exten-sional geodynamic setting. The magma formation reflects a reheating event in the Dabie orogenic belt and it enhances the transfer of tectonic regime from collision into extension and promotes the rapid exhumation into lower crust for the UHP metamorphic rocks.展开更多
文摘The paper reports SHRIMP U-Pb zircon data of a dark eclogite and a post-eclogite garnet-bearing gneissic granitic rock from the Bixiling area, Yuexi County, Anhui Province, in the eastern Dabie Mountains. The eclogite, which is metamorphosed basic tuff, contains very scarce zircons in omphacite or garnet, but more zircons in quartz. They usually exhibit a double-layered texture, as shown clearly in cathodoluminescence images. Their inner main parts give a 206Pb/238U age of 757±7 Ma, representing the approximate age of the high-pressure (HP)- ultrahigh-pressure (UHP) metamorphic event during which the eclogite was formed. The outer peripheral parts of the zircons, which have been modified by late-stage fluids, give an age of 223±3 Ma. The granitic rock contains more zircons of anatectic origin found mostly in feldspar and quartz and usually also showing a similar composite texture. The inner main parts of the anatectic zircons with oscillatory zoning give a 206Pb/238U age of 727±15 Ma for the approximate age of the emplacement of the granitic rock, and their outer parts, an age of 219±3 Ma for a similar or even the same fluid event. It is thus suggested that the HP-UHP metamorphism of the Bixiling eclogite facies rocks took place during the Neoproterozoic Jinningian, and the Indosinian age values may only represent a late event in the nature of fluid activity.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 49794043 and 40073005) and the Ministry of Science and Technology of China (Grant No. G1999075506).
文摘U-Pb zircon dating on two foliated garnet-bearing granite samples in the western Dabie ultra-high-pressure (UHP) metamorphic unit yields concordant ages of (234±4) Ma and (227±5) Ma, respectively. These ages, following the UHP peak metamorphism, represent the magma emplacement ages for the foliated garnet-bearing granites. This, for the first time, shows that there are the Triassic granites in the Dabie Mountains. The foliated garnet-bearing granites resemble A-type granite in geochemical characteristics, indicating that they were formed in exten-sional geodynamic setting. The magma formation reflects a reheating event in the Dabie orogenic belt and it enhances the transfer of tectonic regime from collision into extension and promotes the rapid exhumation into lower crust for the UHP metamorphic rocks.
