Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..505m&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 505-506
Astronomy and Astrophysics
Astronomy
5
Astronomical Models, Chemical Composition, Cooling, Depth, Meteoritic Composition, Crusts, Electron Probes, Pyroxenes, Temperature Effects, Thickness
Scientific paper
Cumulate eucrites have been proposed to be located at the lower part in a eucritic crust on a diogenitic mantle of the Howardite, Eucrite, and Diogenite (HED) parent body. To obtain information on the evolution and the thickness of eucritic crust of the HED parent body, we computed cooling rates and burial depths by modeling both the width of the augite lamella and Ca compositional gradients by numerically solving the diffusion equation of Ca atoms required for augite lamella growth in pyroxene. We determined the best-fit cooling rate (or burial depth) by closely matching the calculated width of augite and Ca gradients of both augite and the host pyroxene to the observed profiles measured by electron microprobe. We assumed the solvus function reported by Lindsley to determine the Ca contents of augite and low-Ca pyroxene at their interface. We used the Ca diffusion coefficients of augite and pigeonite experimentally determined by Fujino et al. The details of calculations are given in Miyamoto and Takeda. These results are consistent with a recent spectral study in which the largest observed eucritic fragment (10 km) sets a lower limit on the thickness of the eucritic crust. The highest termination temperature of Moore County among these cumulate eucrites suggests that Moore County was excavated at relatively high temperature. The burial depths do not correlate with the mg# of pyroxenes in the cumulate eucrites. This result suggests heterogeneous distribution of the crustal materials in the HED parent body.
Miyamoto Manabu
Takeda Hidenori
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