Abstract by Tober Dyorich
Accurate Geochemical Analysis Begins in the Field: A Look at Creons Cave Basalt, Snake River Plain, Idaho
As part of our studies of the petrogenesis of the basalts on the Great Rift, we analyzed a series of samples collected from basaltic spatter at Creons Cave and powdered by collaborators. X-ray fluorescence (XRF) analysis revealed that this spatter either had a complicated history or had been contaminated. The analysis had strong positive Pb anomalies, high concentrations of alkali elements, and high LOIs, which do not correlate with the normal interpretation of a mantle plume origin for similar rocks. The vesicles in whole rock samples were found to have secondary minerals and dust. To remove these contaminants, rocks were first broken into pea-size pieces and washed multiple times in an ultrasonic bath. Then the cleanest rock chips were handpicked, crushed to a powder, and prepared for XRF analysis. Compositions of the washed samples confirmed that the previous batch of samples had been contaminated. The new analyses lack the Pb and alkali anomalies and have the normal low LOIs. This project shows that accurate analyses and interpretations depend on each step of the process, from sample collecting to preparation to analysis.