Trace Element Systematics of Granulite-Facies Rutile

Chen Yi; Chen Si; Su Bin; Li Yibing; Guo Shun

Abstract：Granulite is the most important metamorphic rock type for the study of crust evolution.As a common accessary mineral in granulite,rutile provides a new research window for the evolution of the continental crust.Based on fundamental information for granulite-facies rutile (microtextures,trace elements,and cation substitution) and related trace elements in major rock-forming minerals in the crust,this paper discusses the potential trace element behaviors and diffusion effects during granulite-facies metamorphism,which have received much less attention than eclogite ones during the last decades.The Zr contents in granulite-facies rutile may reflect metamorphic temperatures of different metamorphic stages;however,the formation of secondary zircon and/or ilmenite would significantly affect the Zr contents of former rutile via diffusion effects.The isolated rutile that is not equilibrated with zircon and quartz (e.g.,rutile boundaries close to the secondary zircon and ilmenite,orientated rutile needles in garnet) cannot be used to calculate temperatures by Zr-in-rutile thermometer.The Nb,Ta,Cr and V contents of granulite-facies rutile are largely influenced by bulk-rock composition and by the formation and breakdown of biotite,ilmenite and kyanite.In addition,the Fe contents of rutile adjacent to garnet may be significantly modified due to the fast diffusion rate of Fe.Understanding the behaviors of rutile trace elements during granulite-facies metamorphism can provide important mineral constraints for the metamorphic evolution and dynamic processes of the continental crust.