Pressures and temperatures within a typical parent meteorite body

Abstract

Revised estimates have been made of the metal/silicate and metal/sulphide fractionations for nickel in the stony-iron and iron meteorites, respectively. Assuming equilibrium fractionations at temperatures of about 2000°K, pressures of between 10 4 and 10 5 atm must have been operating within the typical parent meteorite body. Revised estimates of the rate of depression of the γ → α transformation temperatures of nickel-iron alloys with pressure ( Uhig, 1954) suggest iron meteorites have transformed under pressures of approximately 7 × 10 4 atm. Furthermore, if about 10 8 years were available from the time of crystallization of octahedrites, through cooling into transformation regions and to the disruption of the body, the core of the parent body must have cooled to a minimum temperature of 700°K. If graphite was transforming to diamond in the Canyon Diablo octahedrite at 700°K in the core of the parent body, pressures of between 2 × 10 4 and 3 × 10 4 atm must have been operating in the core. This evidence indicates that pressures seem to have a maximum value of between 2 × 10 4 and 10 5 atm while temperatures of approximately 200°K are assumed to have been operating at the time when the mantle of the parent body was crystallized or crystallizing and when the outer metal core at least was still molten. There are indications that the crystallized core had cooled to about 700°K before it was disrupted. The volume of the typical parent meteorite body is likely to have approached that of the moon.