NEW CONSTRAINTS ON THE SLATE ISLANDS IMPACT STRUCTURE, ONTARIO, CANADA

The Slate Islands in northern Lake Superior represent the eroded remai ns of a complex impact crater, originally similar to 32 km in diameter , New field studies there reveal allogenic crater fill deposits along the eastern and northern portions of the islands indicating that this 500-800 Ma impact structure is not as heavily eroded as previously tho ught. Near the crater center, on the western side of Patterson Island, massive blocks of target rocks, enclosed within a matrix of fine-grai ned polymict breccia, record the extensive deformation associated with the central uplift, Shatter cones are a common structural feature on the islands and range from <3 cm to over 10 m in length, Although shat ter cones are powerful tools for recognizing and analyzing eroded impa ct craters, their origin remains poorly constrained.