Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..542t&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 542
Other
7
Meteorites, Meteoritic Composition, Petrography, Pyroxenes, Radioactive Age Determination, Temperature Effects, Crystal Defects, Ejecta, Mars (Planet), Recrystallization
Scientific paper
The ALH 84001 meteorite, long thought to be a diogenite, has recently been reclassified as a martian orthopyroxenite. Unlike the other martian meteorites, ALH 84001 shows evidence for multiple shock events, separated in time by recrystallization of silicates and by aqueous alteration. This history of multiple shock (impact) events suggests that ALH 84001 is older than the other martian meteorites, and might be from an ancient (Hesperian or Noachian) surface on Mars. Petrographic evidence of shock in ALH 84001 includes crush/gouge zones with recrystallized cataclastic texture; strain birefrigence, deformation features, and fractures in pyroxenes; maskelynite after all original plagioclase; radial fractures surrounding chromite and maskelynite grains; grain boundary offsets along some radial fractures; and fault offsets of zoning in carbonate mineral grains. These features did not form in a single shock event because the fault offsets of the carbonate zoning postdate formation of the carbonate; the formation of carbonate postdates recrystallization of the crush/gouge zones; and recrystallization of the crush/gouge zones postdates their formation. Evidence for two shock (impact) events in ALH 84001 suggests that it is not likely to be a product of relatively recent magmatism. To accommodate this shock history, the martian source crater for ALH 84001 must be superimposed on (or adjacent to) older impact materials. Of the few craters on young igneous surfaces on Mars, only a small proportion formed on or near earlier impact features. It is much more likely that ALH 84001 was ejected from an old igneous unit (Hesperian or Noachian age), pocked by numerous impact craters over its long exposure at the martian surface.
No associations
LandOfFree
An ancient age for ALH 84001? Petrographic evidence for multiple shock events does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with An ancient age for ALH 84001? Petrographic evidence for multiple shock events, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and An ancient age for ALH 84001? Petrographic evidence for multiple shock events will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-822044