A Study Of Sudbury Breccias And Shock-metamorphosed Zircons, Ontario, Canada

The Sudbury Structure, formed by meteorite impact at 1850Ma, consists of three major components: (1) the Sudbury Basin; (2) the Sudbury Igneous Complex, which surrounds the basin as an elliptical collar; and (3) breccia bodies in the footwall known as Sudbury Breccia. Sudbury Breccia appears, in general, as subrounded fragments set in a recrystallized fine-grained to aphanitic igneous-textured matrix and is regarded as an important evidence of a meteorite impact.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 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.