Fractionations by impacts or pyroclastic activity

Several kinds of physical processes have been hypothesized to have affected planetesimals prior to their accretion into planets. These processes could conceivably explain some chemical fractionations observed among asteroids and planets. 

Bulk compositions of H, L, and LL chondrites normalized to Cl abundances. Elements are plotted in order of decreasing volatility from left to right. Lithophile, siderophile, and chalcophile elements are designated with open, black, and gray symbols, respectively. These diagrams reveal fractionation of these element groups among different ordinary chondrite classes. Data from Kallemeyn et al. (1989). 

Element fractionation resulting from oxidation/reduction 

Changes in oxidation state can have a significant effect on the volatility of some elements, including cerium, ytterbium, tungsten, and molybdenum, all of which are refractory in reducing conditions but become increasingly volatile as conditions become more oxidizing. 

Concentrations of metallic iron and oxidized iron, normalized to silicon, indicate that both oxidation/reduction and loss of metal are required to explain the compositions of various chondrite classes. 

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