Morphological analysis of olivine grains annealed in an iron-nickel matrix: Experimental constraints on the origin of pallasites and on the thermal history of their parent bodies
Citation
Saiki, K., Laporte, D., Vielzeuf, D., Nakashima, S., & Boivin, P. (2003). Morphological analysis of olivine grains annealed in an iron‐nickel matrix: Experimental constraints on the origin of pallasites and on the thermal history of their parent bodies. Meteoritics & Planetary Science, 38(3), 427-444.Publisher
The Meteoritical SocietyJournal
Meteoritics & Planetary ScienceAdditional Links
https://meteoritical.org/Abstract
Two types of pallasites can be distinguished on the basis of the grain shape of olivine (rounded or angular). It has been suggested that these two types of textures resulted from different degrees of annealing at high temperature in the parent body. In order to characterize the kinetics of rounding of olivine grains in an Fe-Ni matrix, we carried out a series of annealing experiments using a mixture of olivine and Fe-Ni powder. We were able to reproduce, at a miniature scale, the range of textures in pallasites. The rate of rounding was rapid enough to be observed and measured at the scale of a few micrometers to 20 micrometers, even though the experiments were performed below the solidus of the Fe-Ni metal. For instance, grains 14 m in diameter became nearly spherical within 7 days at 1400 degrees C. For the morphological analysis of olivine grains, we used two independent techniques: the "critical diameter method" and the "Gaussian diffusion-resample method," a new technique specially developed for our study. Both techniques indicate that the rounding time scale is proportional to the cube of the grain size and that morphological adjustments in our experiments occurred by volume diffusion in the olivine lattice, not by surface diffusion along the olivine-metal boundaries. We used our experimental data to estimate the time scales required for the development of olivine-metal textures in natural pallasites. We determined that small scale rounding of olivine grains in a solid metal matrix can be produced within relatively short time intervals: 100 years to produce rounded olivine grains 0.1 mm in radius at 1300-1400C.Type
Articletext
Language
enISSN
1945-5100ae974a485f413a2113503eed53cd6c53
10.1111/j.1945-5100.2003.tb00278.x