Using a commercial ceramic adhesive, we have developed a technique by which loose mineral grains may be mounted for electron microprobe (EMP) analyses and imaging prior to 40Ar/39Ar laser microprobe (LMP) dating. Successively applied and cured layers of the adhesive encase mineral grains aligned along the surface of a glass slide; this slide is subsequently ground off to expose the mineral grains for polishing and EMP analysis. Following removal of the conductive coating, irradiation, and heating to 500°C in vacuo (to drive off atmosphere, hydrocarbons, and moisture) the entire grain mount is introduced into the LMP line. Tests of the ceramic's properties were performed by subjecting 125-500μm-diameter grains of a 35.04±0.84-Ma amphibole to the full preparation and analytical regimen. Resulting isotopic data reveal that the ceramic does not interfere with the Ar systematics of the enclosed grains, but does contribute a large component of atmospheric Ar. Curing the grain mounts in a nitrogen atmosphere, and treating them at 700°C in vacuo prior to dating reduces the atmospheric contribution to negligible levels; using laser energies necessary to fuse amphibole grains, heating of the nitrogen-cured, 700°C-treated ceramic fails to evolve significant quantities of any Ar isotopes. This technique is designed for use in the dating of detrital and authigenic grains, each of which may have a different composition and range of inclusion and alteration phases. It is also applicable to the study of other minerals which must be concentrated or processed as grain separates prior to 40Ar/39Ar LMP analysis.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology