Diana Bolser¹, Thomas J. Zega^2,3, Abu Asaduzzaman³, Stefan Bringuier³, Steven B. Simon⁴, Lawrence Grossman⁴, Michelle S. Thompson² and Kenneth J. Domanik^1
1Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, USA
²Lunar and Planetary Laboratory, Department of Planetary Sciences, University of Arizona, Tucson, Arizona, USA
³Department of Materials Science & Engineering, University of Arizona, Tucson, Arizona, USA
⁴Department of Geophysical Sciences, University of Chicago, Chicago, Illinois, USA

A coordinated, electron-backscatter-diffraction (EBSD) and transmission electron microscope (TEM) study was undertaken to obtain information on the origin of rims on refractory inclusions in the Allende and Axtell CV3 chondrites. These measurements were supported by theoretical modeling using density functional theory. Crystal-orientation analysis of Wark-Lovering rims via EBSD revealed pyroxene grains with similar crystallographic orientations to one another in both inclusions. An epitaxial relationship between grains within the diopside and anorthite rim layers was observed in Allende. TEM examination of the rims of both samples also revealed oriented crystals at depth. The microstructural data on the rims suggest that grain clusters grew in the form of three-dimensional islands. Density functional theory calculations confirm that formation of oriented grain islands is the result of energy minimization at high temperature. The results point toward condensation as the mode of origin for the rims studied here.

Reference
Bolser D, Zega TJ, Asaduzzaman A, Bringer S, Simon SB, Grossman L, Thompson MS and Domanik KJ (2016) Microstructural analysis of Wark-Lovering rims in the Allende and Axtell CV3 chondrites: Implications for high-temperature nebular processes. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12620]
Published by arrangement with John Wiley & Sons

Motoo Ito¹ and Scott Messenger^2
1Robert M Walker Laboratory for Space Science, EISD/ARES, NASA Johnson Space Center, Houston, Texas, USA
²JAMSTEC, Kochi Institute for Core Sample Research, Nankoku, Kochi, Japan

We have established analytical procedures for quantitative rare earth element (REE) measurements by NanoSIMS 50L ion microprobe with 2–10 μm spatial resolution. Measurements are performed by multidetection using energy filtering under several static magnetic field settings. Relative sensitivity factors and REE oxide/REE element secondary ion ratios that we determined for the NanoSIMS match values previously determined for other ion microprobes. REE measurements of 100 ppm REE glass standards yielded reproducibility and accuracy of 0.5–2.5% and 5–15%, respectively. REE measurements of minerals of an Allende type-A CAI, 7R19-1, were performed using three different methods: spot analysis, line profile, and imaging. These data are in excellent agreement with previous REE measurements of this inclusion by IMS-3f ion microprobe. The higher spatial resolution NanoSIMS measurements provide additional insight into the formation process of this CAI and offer a promising new tool for analysis of fine-grained and complexly zoned materials.

Reference
Ito M and Messenger S (2016) Rare earth element measurements and mapping of minerals in the Allende CAI, 7R19-1, by NanoSIMS ion microprobe. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12623]
Published by arrangement with John Wiley & Sons