Petrology, structure and origin of the Manicouagan Melt Sheet, Quebec, Canada: A preliminary report Floran ET AL.

Chemical, petrographic, isotopic and field studies of igneous‐textured rocks within the Manicouagan structure indicate that they are the product of impact melting. Features of the melt sheet include a high degree of textural variation combined with chemical homogeneity. The textures record a complex thermal history and are due primarily to the interaction of clasts with melt. An inverse correlation between clast abundance and matrix grain size allows the melt sheet to be divided into three vertically gradational units of variable thickness. Chemical homogeneity indicates that the impact melting process has the first order effect of homogenizing heterogeneous target material. The process, however, is not totally effective, because significant (although small) deviations from a calculated average composition exist, particularly in the basal clast‐laden unit. These differences depend on clast composition and abundance. The results presented here are consistent with proposed models for the generation of terrestrial and lunar impact melts.