Cathodoluminescence (CL) and mineral inclu- sions investigations show that zircons from Yinggelisayi UHP metamorphosed granitoid gneiss in Altyn Tagh exhibit core-mantle-rim internal texture with magmatic residual cor...Cathodoluminescence (CL) and mineral inclu- sions investigations show that zircons from Yinggelisayi UHP metamorphosed granitoid gneiss in Altyn Tagh exhibit core-mantle-rim internal texture with magmatic residual core, the metamorphic overgrowth mantle and the late stage rim. SHRIMP 206 Pb/238U ages of 5 spots from the mantles vary from 484±11 to 491±12 Ma with Th/U ratios from 0.01 to 0.03, yielding a weighted average age of 487±10 Ma (2σ ) as the age of the UHP metamorphosed granitoid gneiss. The 206Pb/238U ages from the oscillatory zoned cores range from 809±19 to 885±21 Ma with Th/U ratios ranging from 0.42 to 0.83, which are interpreted as the crystallization age of the protolith of the granitoid gneiss. The metamorphic age (487±10 Ma) of the UHP metamorphosed granitoid gneiss, well consistent with the peak metamorphic age (about 500 Ma) of the UHP eclogite with crystallization age of the proto- lith between 809±19 and 885±21 Ma at Jianggelisayi in west- ern Altyn Tagh, indicates the existence of a UHPM belt along the south margin of the Altyn Tagh as a result of deep sub- duction during Early Paleozoic age of previously existing continental crust.展开更多
文摘Cathodoluminescence (CL) and mineral inclu- sions investigations show that zircons from Yinggelisayi UHP metamorphosed granitoid gneiss in Altyn Tagh exhibit core-mantle-rim internal texture with magmatic residual core, the metamorphic overgrowth mantle and the late stage rim. SHRIMP 206 Pb/238U ages of 5 spots from the mantles vary from 484±11 to 491±12 Ma with Th/U ratios from 0.01 to 0.03, yielding a weighted average age of 487±10 Ma (2σ ) as the age of the UHP metamorphosed granitoid gneiss. The 206Pb/238U ages from the oscillatory zoned cores range from 809±19 to 885±21 Ma with Th/U ratios ranging from 0.42 to 0.83, which are interpreted as the crystallization age of the protolith of the granitoid gneiss. The metamorphic age (487±10 Ma) of the UHP metamorphosed granitoid gneiss, well consistent with the peak metamorphic age (about 500 Ma) of the UHP eclogite with crystallization age of the proto- lith between 809±19 and 885±21 Ma at Jianggelisayi in west- ern Altyn Tagh, indicates the existence of a UHPM belt along the south margin of the Altyn Tagh as a result of deep sub- duction during Early Paleozoic age of previously existing continental crust.
