Micro-PIXE measurements in meteorites as a source of new information

Most of the present information on the early solar system comes from the investigation of meteorites. Trace-element contents are so far known from bulk analyses, and lateral distributions are known from electron microprobe investigations of the major and minor elements. Distributions of trace elements in single olivine crystals from the unequilibrated chondrites Semarkona and Dhajala are presented. Trace-element zoning in crystals inside chondrules varies strongly even within the same chondrule; but with the general tendency of more pronounced zoning near the chondrule's rim. Trace-element profiles measured in a single, isolated crystal to the contrary show uniform behaviour when going from the crystal's boundary to the interior. We propose a relatively simple model based on diffusion to explain the element distribution within the isolated crystal. From this model it can be concluded that the isolated crystal experienced a short heating to more than 1000 K during its history, that its inclusion into the chondrite came later and that it most probably had never been inside a chondrule. (orig.)