Evidence of Ancient Impact in SW Greenland

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Evidence of Ancient Impact in SW Greenland

Postby David Entwistle » Sun Jul 01, 2012 9:23 am

There are lots of recent news reports of the discovery of an ancient impact structure in Greenland.

The press release from Cardiff University, School of Earth and Ocean Sciences is here.

The press release form the Geological Survey of Denmark and Greenland is here.

The paper: Searching for giant, ancient impact structures on Earth: The Mesoarchaean Maniitsoq structure, West Greenland by Adam A. Garde, Iain McDonald, Brendan Dyck, and Nynke Keulen is published in Earth and Planetary Science Letters.

A 100 km-scale, circular region in the Archaean North Atlantic Craton centred at 65°15′N, 51°50′W 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. The presently exposed features of the Maniitsoq structure were buried 20–25 km below the surface when this event occurred at c. 3 Ga, during waning convergent orogeny. These features include: a large aeromagnetic anomaly; a central 35×50 km2 large area of comminuted quartzo-feldspathic material; regional-scale circular deformation; widespread random fractures with featherlike 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 <c> 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.


The area is here, but, as stated above, there is no obvious evidence of the impact remains in the surface terrain.
David Entwistle
 
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