Dynamic crystallization experiments as constraints on chondrule genesis

The effectiveness of dynamic recrystallization experiments to reconstruct chondrule textures is evaluated. Consideration is given to the results of several experimental simulations of the silicate spheres of pyroxene-olivine chondrules, Si-rich chondrules, chondrites, droplet chondrules, and microporphyritic chondrules. It is shown that many chondrules have textures consistent with heating to 1400-1600 C, and cooling rates from a few degrees to several thousands of degrees per hour. It is shown that this physical constraint effectively rules out mechanisms for chondrule genesis which do not require instantaneous or very slow cooling. Analysis of the available textural, chemical, and isotopic data suggest that chondrules were generated from primordial particles, and several mechanisms might have assisted in chondrule heating as they settled down toward the median plane of the nebula. The most important of these mechanisms appear to be friction with the nebular gas and heating by flares.