Abstract:

It is widely accepted that the Sudbury structure formed by large bolide impact. To find more supporting evidences we have used electronbeam scanning microscopy and Raman microspectroscopy to document the microstructures and phase transformation in zircons from the fragments of the Sudbury breccias which are among the most prominent features of the Sudbury structure. In addition to the important peaks for zircon, two additional Raman peaks at 640 cm-1 and 817 cm-1 are shown. These two additional peaks match with those from a synthetic ZrO2 polymorph containing 05 wt％ TiO2 and fayalite, respectively. Our data show that planar microstructures in three directions and decomposition of zircon to form a ZrO2 polymorph plus fayalite (ZrSiO4+2FeOZrO2+Fe2SiO4) are common in the Sudbury zircons we have examined. These features support an impact origin for the Sudbury breccias and thereby the Sudbury structure at large.

Key words: Sudbury breccia, shockmetamorphosed zircon, phase transformation