Effects Of Radiation Damage In Natural Zircon On The Formation Of High Pressure Mineral Of Reidite

Under high pressure,zircon can be transformed reidite,which is often found inmeteoritic craters in nature and serves as an important indicator for meteoritic craters.By using heavy ion irradiations in zircon,Glasmacher et al.(PRL,2006)and Lang et al.(EPSL,2008)simulated effects of alpha-decay induced radiation damage on the formation of reidite.The result of Glasmacher et al.suggested a promotion of the reidite phase by radiation damage,while that of Lang et al.indicated an seemlying opposite result at a very high dose of ion irradiations.In addition,swift ion induced nuclear tracks are different from the defects produced by?-recoils.Therefore,in order to explain the apparent discrepancy on radiation damage effects on the formation of high pressure phase of reidite,this paper compares three natural zircon having different degrees of irradiation damage with a synthetic zircon having no irradiation damage.The degree of radiaton damage was calculated by the age and the content of U and Th in natural zircon.Synchrotron radiation X-ray diffraction was used to study the influence of radiation damage on the high pressure phase transformation in zircon.Our results show that the phase transformation into reidite from the synthetic zircon(without radiation damage),the Pakistan zircon(10¹⁶ event/g),the Mud Tank zircon(10¹⁷ event/g),and the Bancroft zircon(10¹⁹ event/g),starts at 14.2?19.5,15.7?17.1,18.4?21.5 and 22.5?26.4 GPa,respectively.The Bancroft zircon has the highest radiation damage,and the lowest ratio of reidite after high pressure.We therefore conclude the full amorphization of zircon at high dose of alpha decay events hampers the formation of high pressure phase of reidite,which agrees well with the previous result that the irradiations of high dose high energy ions(5×10¹² Xe/cm²)hinders the structural transformation.