Combined TEM, NanoSIMS, Synchrotron XRF and STXM study of presolar grains and surrounding pristine matrix mineralogy with special emphasis on Acfer 094 and ALH77307

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It is well documented that Acfer 094 and ALH 77307 are two of the most pristine meteorites ever found. The unusual high amount of presolar grains (> 160 ppm silicates, > 25 ppm oxides - Acfer094) within the matrix mineralogy combined with the recent development of site specific (FIB) and large area (ArIS) thin film preparation techniques for TEM investigations enable us to study the main and trace element content as well as structural characteristics of a large set of presolar silicates. The presolar grains and surrounding matrix mineralogy will be studied by TEM, NanoSIMS, synchrotron induced Nano-XRF and STXM. During the first project phase we not only developed the required preparation and measurement procedure but already identified 9 presolar grains applying the NanoSIMS technique within two successfully prepared large area thin films. The complete chemical and structural characterization of these grains will be the next important step. In addition we will extend our work to presolar grains from pristine CR-clan meteorites, which will be identified by a co-operated project (see proposal by Hoppe and Zipfel). The comprehensive study of presolar silicates will enable us to assess the conditions of formation around their parent stars, to reconstruct condensation - crystallization processes and to identify signs of processing in the ISM including amorphisation and re-crystallisation. We will also study the genetic relationship with the surrounding meteorite matrix. Thus, our multi-analytical studies of presolar grains and their surrounding matrix material will give us detailed information on the material from which our solar system formed.