Genesis of zircon and its constraints on interpretation of U-Pb age

作     者：WUYuanbao ZHENGYongfei 

作者机构：SchoolofEarthandSpaceSciencesUniversityofScienceandTechnologyofChinaHefei230026China 

出 版 物：《Chinese Science Bulletin》 (中国科学通报)

年 卷 期：2004年第49卷第15期

页      面：1554-1569页

核心收录：

学科分类：070902[理学-地球化学] 0709[理学-地质学] 07[理学] 

基　　金：National Natural Science Foundation of China NSFC: 40303303 40334036 

主　　题：U-Pb定年 锆石 内部结构 示踪元素 矿物包含物 同位素地质年代学 

摘      要：Zircon U-Pb dating is the most commonly used method for isotopic geochronology. However, it has been a difficult issue when relating zircon U-Pb ages to metamor- phic conditions in complex metamorphic rocks. Much pro- gress has been made in the past decade with respect to the genesis of zircon and its constraints on interpretation of U-Pb age. Three methods have been proposed to link zircon U-Pb age to metamorphic conditions: (ⅰ) internal structure; (ⅱ) trace element feature; (ⅲ) mineral inclusion composition. Magmatic zircon shows typical oscillatory zoning and/or sector zoning, whereas metamorphic zircon has internal structures such as no zoned, weakly zoned, cloudy zoned, sector zoned, planar zoned, and patched zoned ones. Zircons formed in different geological environments generally have characteristic internal structures. Magmatic zircons from different rock types have variable trace element abundances, with a general trend of increasing trace element abundances in zircons from ultramafic through mafic to granitic rocks. Zircons formed under different metamorphic conditions have different trace element characteristics that can be used to relate their formation to metamorphic conditions. It is an effective way to relate zircon growth to certain P-T condi- tions by studying the trace element partitioning between coexisting metamorphic zircon and garnet in high-grade metamorphic rocks containing both zircon and garnet. Pri- mary mineral inclusions in zircon can also provide unambi- guous constraints on its formation conditions. Therefore, interpretation of zircon U-Pb ages can be constrained by its internal structure, trace element composition, mineral inclu- sion and so on.