Manifestation of shock in plagioclase from shatter coned gneisses, Manicouagan impact structure.
Previously Published Material: I have previously presented preliminary microscopy and field observations associated with this work at Charlotte GSA and 2014 LPSC. This will be the first time presenting the Raman and FESEM work.
Abstract ID#: 34442
Quartz grains within gneisses at 27 km rarely exhibit single sets of decorated PDFs. Oligoclase exhibits minor fracturing and development of fine planar features within twins. At a 15 km radius from the centre of the structure, multiple orientation, decorated PDFs are ubiquitous within quartz grains and multiple orientation, fine scale planar features are well developed within twins in oligoclase. In thin section, the gneiss has a “cloudy” appearance, owing to the preponderance of planar features in both the plagioclase and quartz. The shatter coned gneisses at 12 km radius, are even darker in thin section. Quartz grains exhibit high densities of multiple orientation, decorated PDFs, which give the grains a “toasted” appearance. Oligoclase grains also exhibit high densities of multiple orientation planar features within twins and the development of extensive isotropic, glassy-looking domains.
Shatter cones from the anorthositic gneiss central uplift at Manicouagan, 4 km radius from the centre, exhibit fractured labradorite grains. The intensity of the fracturing increases towards shatter cone surfaces. Fine scale, multiple planar features within twins, are only manifest in labradorite grains immediately adjacent to shatter cone surfaces.
This work summarizes the results of a Raman and FESEM investigation of oligoclase and labradorite grains from shatter cones at Manicouagan. This will allow a better understanding of the mechanisms of shatter cone formation, as well as the response of plagioclase to shock. Future work will aim to further constrain and calibrate shock in plagioclase.