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

We performed impact experiments into mixtures of chondrule analogs and different 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 our study 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−1 and 1200 m s−1. 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 (porosities) between ϕ = 0.70 (30%) and ϕ = 0.99 (1%) which covers the observed range of volume filling factors of carbonaceous chondrites (CC) and ordinary chondrites (OC). From our experiments, we expect CM chondrites to be likely compacted in a pressure range between 60 and 150 MPa, CV chondrites appear to be compacted with pressures between 100 and 500 MPa, and for OCs we only determined a lower limit of the compaction pressure of 150 MPa. These dynamic compaction pressures are in good agreement with the typical shock stages of the chondrites, and thus can confirm that CM chondrites are less shocked than CV chondrites and significantly less shocked than OCs. Finally, we found a factor of 10 difference in the dynamic-pressure compaction range of CCs and OCs that allows us to infer either a larger distance between the formation location of the two chondrite families than current models predict or a strong difference in orbital eccentricities for the two groups. As for the high-density rims found around chondrules, we can show that these do not form in dynamic compaction processes as studied in this paper.