Evaluation of dehydration mechanism during heating of hydrous asteroids based on mineralogical and chemical analysis of naturally and experimentally heated CM chondrites
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2008
Received: 1 March 2008
Accepted: 17 May 2008
Published: 8 September 2008
Based on the evidence derived from spectroscopic observation and meteorite analysis, some hydrous asteroids were heated and dehydrated for a certain period of time after aqueous alteration. In order to reproduce the dehydration processes, we experimentally heated Murchison CM chondrite at 600°C for 1 h (600°C/1 h), 600°C/96 h, 900°C/1 h, and 900°C/96 h under controlled oxygen partial pressures. The experimental products were compared with Belgica (B-)7904 CM chondrite, a meteorite from a dehydrated asteroid in terms of characteristic mineralogical and compositional properties. B-7904 shows properties intermediate between the two experimental products heated at 900°C/1 h and 900°C/96 h. In addition, the presence or the absence of some temperature-sensitive minerals in B-7904 suggests that it experienced heating at a temperature higher than 700°C but lower than 890°C. The duration of heating, based on the diffusion time needed to achieve the Fe-Mg zoning profile in olivine in B-7904, was estimated to be between 10 and 103 days at 700°C and between 1 to 102 h at 890°C. The obtained durations are much shorter than those expected from the internal heating model which requires prolonged heating over million years. Therefore, it is unlikely that the short-lived radionuclide of 26Al is a heat source for the dehydration of B-7904. Instead, short-duration local heating, such as that from impacts or solar radiation, is a more promising heat source.