Impact-Generated Dykes and Shocked Carbonates from the Tunnunik and Haughton Impact Structures, Canadian High Arctic

• Main Author: Newman, Jennifer D
• Format: Text
• Language: English
• Published: Scholarship@Western 2020
• Subjects: impact crater; breccia; carbonate; melt rock; Arctic; shock; Geology
• Online Access: https://ir.lib.uwo.ca/etd/6950; https://ir.lib.uwo.ca/context/etd/article/9372/viewcontent/auto_convert.pdf

The Canadian High Arctic contains two impact structures created by hypervelocity impact events in carbonate-rich target rocks. The remote locations of the Tunnunik and Haughton impact structures means that there are aspects of these impact structures which have yet to be fully investigated. This study characterizes the range of impact-generated dykes exposed from both impact structures which include lithic breccias, impact melt-bearing breccias, and impact melt rocks. Breccias may include silicate impact glass fragments and evidence for carbonate melt. Impact melt rocks from the Haughton impact structure contain the rare terrestrial mineral moissanite. This is only the third reported occurrence of moissanite associated with an impact structure and the first to observe its presence in situ. Inclusions and variation of polytypes in moissanite provide information regarding high temperatures present during crater formation. The carbonate-rich rocks that form these impact structures contain well-developed shatter cones as evidence of shock metamorphism. As a shock classification system does not currently exist for carbonates, the effect of shock on the crystal structure of calcite and dolomite is examined using X-ray diffraction to better understand the extent of strain in both these minerals. Previous studies of shocked carbonates from terrestrial impact structures is limited and the goal here is to assign numerical values to indicate strain and thereby better quantify and compare shock in carbonates among impact structures. The parallel studies of impact-generated dykes and shock at the Tunnunik and Haughton impact structures allow for the comparison of two impact structures with similar diameters, 28-km for Tunnunik and 23-km for Haughton, in different states of preservation. The deeply eroded Tunnunik impact structure and well-preserved Haughton impact structure provide insights into complex crater formation in carbonate rich rocks that would otherwise not be available by only studying one site. Results from this ...