2008 Joint Annual Meeting (5-9 Oct. 2008): The Anorthositic Central Uplift of the Manicouagan Impact Structure

The Manicouagan impact crater, located at 51˚30'N, 68˚30'W in eastern Quebec, was formed by meteorite impact at 214±1 Ma. This well-preserved, undeformed structure is a ~100 km diameter complex crater formed in predominantly crystalline rocks of the Grenville province. Weathering and episodic glacial scouring have eroded and exposed its internal structure, which makes Manicouagan a valuable source of data. The rock types, level of preservation, and good outcrop at Manicouagan have the potential to facilitate comparisons with other planetary bodies; in particular the Moon.

The intention of this study is to establish how the central uplift at Manicouagan was emplaced. Impact scaling laws suggest it has undergone 10 – 15 km of rapid structural uplift. Four months of field work investigating the central uplift reveals a core of metamporhosed anorthositic rocks, that constitute Mont de Babel (957 m) and Maskelynite Peak (945 m), and associated high-grade, granitic and metabasic gneisses. These rocks retain their overall coherency (i.e., are not breccias), but are interspersed with pseudotachylite veins typically 1 mm to 15 cm thick. Sporadically distributed anastamosing, multi-vein pseudotachylite systems, 1 to 2 m wide, are interconnected by more pervasive subsidiary veins that occur at angles to these multi-vein zones. Where observed, offset associated with the pseudotachylite zones is typically 20-30 cm. Initial results indicate that the pseudotachylite systems have facilitated movement within the host rocks, but are unlikely to have enabled kilometer-scale displacements necessary for central uplift formation.