The use of a neon inductively coupled plasma (Ne ICP) in place of an argon inductively coupled plasma (Ar ICP) for laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS) is demonstrated. Gas blank mass spectra were obtained comparing the signals obtained with an Ar ICP with the Ne ICP. Sensitivity (signal/concentration) data were also obtained for a number of analytes using solid reference materials. The sensitivity data is complicated by significant changes in optimum Ne ICP parameters (especially nebulizer gas flow) for analytes of varying mass. The sensitivity of the Ne ICP is in general also lower than that obtained for the Ar ICP. The potential for the Ne ICP to reduce the formation of argides, both in the background and from sample induced interferences, is demonstrated. Clearly shown is the reduction of the interferences of 63Cu40Ar and 65Cu40Ar on 103Rh and 105Pd in a Cu2S sample, as well as the reduction of the interferences of 58Ni40Ar and 60Ni40Ar on 98Ru and 100Ru in a NiS sample.
Clinopyroxene/melt pairs in strongly potassic silicate and carbonatite melts exhibit unusually high U/Th partitioning ratios of 3 and 2, respectively. These values are much higher than those found for aluminous clinopyroxenes in peridotite, and have the potential to cause signi®cant ( 230 Th)/ ( 238 U) isotope enrichment in volcanics. The potassic silicate (lamproite) and carbonatite melts correspond closely to the main agents of mantle metasomatism, indicating that clinopy-roxene in metasomatized regions of the mantle may greatly affect U/Th disequilibria. Recycling of alkali pyroxenite veins in the oceanic lithosphere formed by solidi®cation of melt in the extremities of the MORB melting region presents an alternative to eclogite recycling in MORB and OIB genesis.
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