Searching for giant, ancient impact structures on earth: the Mesoarchaean Maniitsoq structure, West Greenland

• Published in: Earth and Planetary Science Letters
• Main Authors: Garde, Adam A., McDonald, Iain, Dyck, Brendan, Keulen, Nynke
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2012
• Subjects: QB Astronomy; QE Geology; Greenland; Maniitsoq; North Atlantic
• Online Access: https://orca.cardiff.ac.uk/id/eprint/44575/; https://doi.org/10.1016/j.epsl.2012.04.026

A 100km scale,circular region in the Archaean North Atlantic Craton centred at 651150N, 511500W near Maniitsoq town in West Greenland comprises a set of highly unusual geological features that were created during a single event involving intense crushing and heating and are incompatible with crustal orogenic processes. Th presently exposed features of the Maniitsoq structure were buried 20–25 km below the surface when this event occurred at c.3Ga,during waning convergent orogeny.These features include: a large aeromagnetic anomaly; a central 35x50 km2 large area of comminuted quartzo-feldspathic material; regional-scale circular deformation; widespread random fractures with feather like textures; intense fracture cleavage; amphibolite–granite-matrix breccias unrelated to faulting or intrusions; formation and common fluidisation of microbreccias; abundant evidence of direct K-feldspar and plagioclase melting superimposed on already migmatised rocks; deformation of quartz by oc4 slip; formation of planar elements in quartz and plagioclase; and, emplacement of crustally contaminated ultramafic intrusions and regional scale hydrothermal alteration under amphibolite-facies conditions. The diagnostic tools employed to identify impacting in the upper crust are inadequate for structures preserved deep within the continental crust. Nevertheless,the inferred scale, strain rates and temperatures necessary to create the Maniitsoq structure rule out a terrestrial origin of the structure.