Ar-40/Ar-39 age of the Shergotty achondrite and implications for its post-shock thermal history

Details Ar-40/Ar-39 age of the Shergotty achondrite and implications for its post-shock thermal history Ar-40/Ar-39 age of the Shergotty achondrite and implications for its post-shock thermal history

Jul 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979gecoa..43.1047b&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 43, July 1979, p. 1047-1055.

Computer Science

17

Achondrites, Argon Isotopes, Feldspars, Meteoritic Composition, Shock Heating, Temperature Effects, Case Histories, Neutron Irradiation, Stony Meteorites, Surface Temperature, Isotopic Ratios, Meteorites, Achondrites, Shergotty Meteorite, Ages, Thermal History, Shock Metamorphism, Argon/Argon, Isotopes, Analysis, Samples, Meteorite, Maskelynite, Temperatures, Diffusion, Models, Cooling, Parent Bodies, Collisions, Experiments, Data, Plagioclase, Outgassing, Dating Techniques, Cosmic Rays, Exposure Ages, Chon

Scientific paper

Ar-40/Ar-39 measurements are used to determine the age of the Shergotty achondrite and the chronology of the shock event responsible for the complete conversion of its plagioclase to maskelynite is discussed. Apparent ages are found to vary between 240 and 640 million years for the whole rock sample, with a plateau age of 254 million years for a maskelynite separate. The Rb-Sr age of 165 million years determined by Nyquist at al (1978) suggests that the maskelynite as well as the whole rock was incompletely degassed. Argon diffusion characteristics indicate a post-shock cooling time greater than 1000 years and a burial depth greater than 300 m for a thermal model of a cooling ejecta blanket of variable thickness. It is concluded that the shock event which degassed the argon and reset the Rb-Sr systematics occurred between 165 and 250 million years ago when the parent body experienced a collision in the asteroid belt.

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