Program > Browse abstracts by speaker > Klemme Stephan

Conventionally, trace elements in experimental run products are analysed with SIMS or LA-ICPMS techniques using single spot analyses. Even with the most advanced laser ablation systems the crystal sizes need to be at least about 10 µm across to determine meaningful trace element concentrations. However, many experimental run products contain crystals that are smaller than this and often these experiments are simply discarded and a lot of time and effort is spent to synthesize homogeneous phases larger than this.

Here we present an alternative method to determine trace element concentrations in small and acicular apatite crystals using LA-ICPMS trace element mapping techniques. The experimental run product examined here contains mostly 10-15 µm sized acicular apatite crystals and a quenched carbonatite melt. The experimental details, the partition coefficients, and the geological implications will be presented elsewhere (c.f., Bach et al., this conference). Single spot LA-ICPMS analyses and laser ablation trace element maps were produced using a new Teledyne Iridia laser system coupled to a conventional Thermo quadrupole ICP-MS. We used laser sizes of 10 µm for the single spots and square 5 µm spots for mapping. The single spot data were reduced using the Glitter software package and the maps were processed using the Teledyne HDIP software.

The following convenient procedure has been established in our laboratories: (1) JEOL Hyperprobe: major element maps and BSE imaging. (2) Transfer of coordinates to the LA-system, programming the trace element map. (2) HDIP software to identify crystals and melt patches using highly incompatible or highly compatible elements. Here we used Ta, as Ta concentrations are very low (< 10 µg/g) in apatite and much higher in coexisting melts (≥150 µg/g). We then compared partition coefficients derived from trace element mapping with data from single spot analyses, and our results indicate very good agreement.