Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2K082

Experiments on the consolidation of chondrites and the formation of dense rims around chondrules

Beitz, Eike (TU Braunschweig, Institut für Geophysik und extraterrestrische Physik)
Güttler, Carsten (TU Braunschweig, Institut für Geophysik und extraterrestrische Physik)
Nakamura, Akiko (Kobe University, Department of Earth and Planetary Sciences)
Blum, Jürgen (TU Braunschweig, Institut für Geophysik und extraterrestrische Physik)

It is generally accepted, that chondrites are formed by coagulation of chondrules and the matrix dust. Such pre-chondrites can be formed in low-velocity collisions and would therefore be more porous than the typical chondrites are. Those chondrites have volume filling factors (porosity) ranging from φ=0.3 (70%) to φ=0.6 (40%). We will present impact experiments into mixtures of chondrule analogs and dust materials to determine the dynamic pressure range under which these can be compacted to achieve porosities found in chondritic meteorites. The second objective of the experiment was to test whether or not fine-grained dust rims around chondrules can be formed due to the dynamic compaction process. In our experiments, aluminum cylinders were used as projectiles to compact the chondrite-analog samples in a velocity range between 165 m/s and 1200 m/s. The resulting impact pressures in the samples fall between ~90 and ~2400 MPa. To measure the achieved porosities of our samples, 25 samples were analyzed using computer-aided tomography. We found volume filling factors to be between φ= 0.70 and φ= 0.99. Additionally, we determined the mean pressure range in which CM chondrites were likely to be compacted and found values between 60 and 150 MPa. As for the high-density rims found around chondrules, we can show that these do not form in dynamic compaction processes. Moreover, we found that for a collision between two pre-chondritic bodies of 0.4< φ < 0.5, the collision velocity for a pressure range of 0.05 GPa to 2 GPa falls between 100 m/s and 2000 m/s, which is within the typical velocity range of the of planetary growth models and agrees with a formation distance of chondrites between 2 and 3 AU at given orbital eccentricities of 0.02 and 0.1 for the pre-chondrites.

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