Discovery of oriented zircon growing in the shear process of the Altun (Altyn) fault and its significance:Evidence from microstructure and mineral inclusions in zircon

A suite of granitic and amphibolitic mylonite formed in the process of strike-slip shear is ex-posed in the central segment of the Altun(Al tyn)fault belt.Three types of zircon are identified from the mylonite:long-prismatic zircon,prismatic zircon of magmatic origin and subrounded zircon of metamor-phic zircon.The three types of zircon are more or less different in respect to their microstructural features and mineral inclusions therein.Of these types,long-prismatic zircon grains are oriented in the rock,with their long axis oriented in the same direction as the stretching lineation and the long axes of all the miner-al inclusions therein being parallel to that of the zircon,i.e.to the direction of stretching lineation.Raman spectrum study indicates that the inclusion minerals show the melting phase feature,and cathodolumines-cence images show that this type of zircon has a relatively homogeneous internal structure.Therefore,the long-prismatic zircon resulted from rapid oriented growth in a partial melting regime in the ductile shear process.It not only denotes the direction of shear strain in the strike-slip shear,but the growth age(crys-tallization age)of this type of zircon denotes the age of strike-slip shear.