SHRIMP U-Pb zircon ages for the UHP metamorphosed granitoid gneiss in Altyn Tagh and their geological significance

• Published in: Chinese science bulletin 2004-12, Vol.49 (23), p.2527-2532
• Main Author: ZHANGAnda LIULiang SUNYong CHENDanling WANGYan LUOJinhai
• Format: Article
• Language: English
• Subjects: SHRIMP技术; UHP; 分析方法; 地质学; 地质年代; 片麻岩
• ISSN: 1001-6538; 1861-9541
• DOI: 10.1360/03wd0502

Cathodoluminescence (CL) and mineral inclusions 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 stagerim. SHRIMP ^206Pb/^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±10Ma) of the UHP metamorphosed granitoid gneiss, well consistent with the peak metamorphic age (about 500Ma) of the UHP eclogite with crystallization age of the protolith between 809±19 and 885±21 Ma at Jianggelisayi in western Altyn Tagh, indicates the existence of a UHPM belt along the south margin of the Altyn Tagh as a result of deep subduction during Early Paleozoic age of previously existing continental crust.