Autor Thema: 3 Milliarden Jahre alter Meteoritenkrater in der Maniitsoq Region, Westgrönland  (Gelesen 768 mal)

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3 Milliarden Jahre alter Meteoritenkrater in der Maniitsoq Region in Westgrönland

http://www.sciencedaily.com/releases/2012/06/120628164658.htm

http://maps.google.de/maps?q=65%C2%B015%E2%80%B2+N,+51%C2%B050%E2%80%B2+W&hl=de&ie=UTF8&ll=65.199164,-51.394043&spn=1.730615,3.845215&sll=65.257497,-51.836586&sspn=0.053957,0.120163&t=m&z=8

Adam A. Garde, Iain McDonald, Brendan Dyck, Nynke Keulen. Searching for giant, ancient impact structures on Earth: The Mesoarchaean Maniitsoq structure, West Greenland. Earth and Planetary Science Letters, 2012; 337-338: 197 DOI

http://www.sciencedirect.com/science/article/pii/S0012821X12001938

Zitat
Abstract

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.

 

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