Computational protocol: Dissecting the Re-Os molybdenite geochronometer

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Protocol publication

[…] Elemental and isotopic mapping was carried out using a CAMECA NanoSIMS 50 L at the University of Western Australia. The analysis was performed with an O− beam generated by a Hyperion (H200) RF plasma oxygen ion source. The beam current was approximately 17 pA and the spot size was approximately 100 nm. Each area of interest was pre-sputtered with the primary beam to a dose of >1 × 1017 ions/cm2. Due to the geometry of the mass spectrometer, it was not possible to collect all the relevant isotopes simultaneously, thus each area was mapped twice using two different configurations of the multicollection system. The magnetic field was fixed, and the electron multiplier (EM) detectors were positioned to collect signal from 56Fe, 63Cu, 98Mo, 107Ag, 185Re, 190Os during the first run, and then the last two detectors were moved to collect 187Re and 192Os during the second run. The peak positions were calibrated using pure Re and Os metal standards. As sensitivity was a key issue and there were no significant mass interferences, no slits were used in the mass spectrometer.Images were acquired with a raster size of 45 or 50 μm2, at a resolution of 512 × 512 pixels, with a dwell times of 25 or 30 ms/pixel. Maps were corrected for 44 ns deadtime on each individual pixel. Images were processed using the OpenMIMS plugin for FIJI/ImageJ (https://github.com/BWHCNI/OpenMIMS). […]

Pipeline specifications

Software tools OpenMIMS, ImageJ
Applications Mass spectrometry imaging, Microscopic phenotype analysis
Chemicals Molybdenum, Osmium, Rhenium