The Allochthonous Polymict Breccia Layer of the Haughton Impact Crater, Devon Island, Canada

• Published in: Meteoritics
• Main Authors: Redeker, H.‐J., Stöffler, D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1988
• Subjects: General Earth and Planetary Sciences; General Environmental Science; Canada; Devon Island
• Online Access: http://dx.doi.org/10.1111/j.1945-5100.1988.tb01281.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1945-5100.1988.tb01281.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.1988.tb01281.x

Abstract— The central allochthonous polymict breccia of the Haughton impact structure is up to about 90 m thick and as much as 7.3 km in radial extent. It has been analyzed with respect to modal composition, grain‐size characteristics, and degree of shock metamorphism for the grain‐size ranges 10–∼ 50, 1–10, 0.03–1, and <0.03 mm. The mineralogy of the breccia matrix is dominated by dolomite and calcite, with minor amounts of quartz, other silicate minerals, and rare melt particles. The following lithic clasts have been identified in the 1–10 mm size fraction (averages of vol.% given in parentheses): dolomitic rocks (51), limestones (29), crystalline rocks (10), sandstones and siltstones (3.7), chert (0.7), melt particles (1.9). The mineral clasts (1–0.03 mm) comprise (with decreasing frequency) dolomite, quartz, calcite, feldspar, biotite, amphibole, garnet, opaques, rounded quartz derived from sandstones and accessory minerals. Lithic and mineral clasts display various degrees of shock. Fragments of crystalline rocks are shocked in the 0–60 GPa range; whole rock melts from the crystalline basement are lacking and unshocked rocks are very rare. In contrast, shock‐melted sandstones, shales, and chert were found in most samples. Large clasts of these melt rocks are highly concentrated near the center of the crater. Otherwise, no distinct change of the modal composition with radial range has been observed except that the frequency of limestone clasts increases slightly with radial range. The breccia near the center is more fine‐grained than that beyond about 1 km radius and the sorting parameter increases somewhat with radial range. Except for the high concentration of shock‐melted sedimentary rocks and highly shocked crystalline rocks near the center of the crater, the distribution of shock stages within the lithic clast population is quite uniform throughout the breccia formation. We conclude that the breccia constituents are derived from the lower part of the target stratigraphy (deeper than about 800 m) ...