Dataset: EPR 9-10 North Electron Microprobe Wavelength Spectroscopy

Electron microprobe wavelength dispersive spectroscopy data were collected from hydrothermally active chimneys and inactive off-axis massive sulfide deposits at East Pacific Rise (EPR) 9.50°N during 2019–2021 on cruises AT42-09, AT42-21, and RR2102. Samples were collected using the HOV Alvin or ROV Jason II. Samples were placed in a positive-pressure glove bag flushed with N₂(g), sparged with N₂, heat-sealed into Mylar bags containing AnaeroPaks, and stored at −20 °C. Epoxy-embedded petrographic thin sections were prepared from these samples. Subsamples were dried for 24 hours under N₂(g), vacuum-embedded in epoxy resin (Struers EpoFix Resin, 1 L kit; Part #40200030) following the manufacturer’s guidelines, and cured under N₂(g) for 24 hours. Each epoxy-embedded sample was pre-cut using a wafering saw and then sent to Spectrum Petrographics, Inc. (Washington, USA) for preparation as 30 µm thick, double-polished thin sections mounted on quartz slides, using methods designed to limit sample exposure to water and ambient air. When not in use, thin sections were stored under N₂(g) to limit oxidation.