Evidence for the shock melting of sulfates from the Haughton impact structure, Arctic Canada

Sulfate minerals can form an important component of the matrix to carbonate-rich impact melt breccias at the 24 km diameter, 23 Ma Haughton impact structure, Arctic Canada. The textural and chemical features of the matrix-forming sulfates indicate that these phases, in addition to co-existing carbonates and silicates, crystallized directly from an impact-generated melt. Evidence for this includes (1) the matrix-supported nature of the crater-fill lithologies, (2) sulfate–carbonate–silicate liquid immiscible textures, (3) possible quench textures in anhydrite, and (4) flow textures developed between anhydrite and silicate-rich glasses. Further supporting evidence includes the presence of Si, Al and Mg in the anhydrite structure, which were probably ‘trapped’ by quenching from a melt. Irregular blebs and globules of shock-melted carbonates within anhydrite also suggest a common origin for the two phases. Field studies reveal that clasts of anhydrite-bearing target material are also present in the crater-fill deposits. Several clasts of anhydrite–quartz lithologies exhibit evidence for incipient shock melting in both phases. Previous assumptions about the response of sulfates and carbonates to hypervelocity impact (i.e., lack of melting) may, therefore, be incorrect.