Sx100 electron microprobe

Major and trace element compositions of the olivine phenocrysts from four polished thin sections were analyzed using a Cameca SX 100 electron microprobe at the University of Manchester. A total of 350 spot measurements were taken from 66 olivine phenocrysts. All analyses were performed using a beam current of 20 nA and an accelerating voltage of 15 kV. Counting times for all elements (Si, Al, Cr, Fe, Mn, Mg, Ca, Na, K, Ni and Co) was 60 s, determined as the optimal configuration to obtain the best detection limits. Prior to analysis the background and sensitivity of the microprobe was determined using well‐characterized silicate, oxide, and metal standards (Gregory et al., 2017).

All experimental glasses were analyzed quantitatively by using a Cameca SX-100 electron microprobe at the AMNH. Fifteen data points were collected per sample to measure the concentration of all major and minor elements other than H₂O (Na, K, Mg, Ca, Al, Si, Ti, Fe and Cl) in the glass. An accelerating voltage of 15 kV was applied using a 10-μm beam size, beam currents of 5 nA (Na, K), 10 nA (Mg, Ca, Al, Si, Ti) and 40 nA (Cl) and counting times of 5 s (Na), 10 s (K), 20 s (Mg, Ca, Al, Si, Ti) and 120 s (Cl). Prior to each analytical session, the microprobe was calibrated by using the standards diopside (Si, Ca, Mg), jadeite (Na), orthoclase (K and Al), rutile (Ti), fayalite (Fe) and scapolite (Cl). The standardization process was checked by measuring three internal standards (basalt, andesite and rhyolite) prior and after each session. The results of the experimental glass analyses were normalized to 100% and are listed in Table S1 (Supplementary Material). Since magnetite was the only mineral phase in all samples, and Fe loss to the AuPd capsule is negligible at wet and oxidizing conditions^{37 (link)}, the wt% concentration of magnetite (Fe₃O₄) was easily calculated from the FeO concentration in the residual glass by difference to the fully glassy starting composition P1D.

Major elements in melt inclusions and their plagioclase hosts were analyzed at Oregon State University^{28 ,29} . Major elements in mid-Atlantic ridge phenocryst-host pair samples (A11-107-7-20; TR138-9D; EN025-6D; EN025-2D) were measured using a Cameca SX 100 electron microprobe at the University of Tennessee at an accelerating voltage of 15 kV. Plagioclase was analyzed at a current of 10 nA using a 5 μm spot, with count times of 20 s on peak for Si, Ti, Al, Na, and K, 30 s on peak for Ca, and 60 s on peak for Fe. Glass was analyzed at 20 nA with a 15 μm spot, using count times of 20 s for Si, Al, Mg, Ca, S, Na, and K, and 30 s for P, Ti, Fe, Mn, and Cr. Background count times were 15 s. Natural and synthetic reference materials were employed, and data were processed using a ZAF correction applied using the Cameca PAP procedure. Results are reported in Supplementary Data 1.

The chemical composition was measured using a CAMECA SX100 electron microprobe operating in wavelength-dispersive spectrometry mode at 15 kV, 10–20 nA and using natural standards (Full description of the methodology is summarized in ref. 2 (link)). The single-crystal X-ray data were obtained using SuperNova Dual diffractometer with a mirror monochromator (MoKα, 0.71073 Å) and Atlas CCD detector. The structure was solved by direct methods, with subsequent analyses of difference-Fourier maps, and refined with neutral atom scattering factors using SHELX97^{50 (link)}. Experimental details for untreated and annealed crystals summarized in supplementary file in Table S3. The Raman experiment was performed using WITec confocal CRM Alpha 300 Raman microscope at excitation laser line λ = 488 nm and CCD detector. The spectra were collected in the range between 4000–120 cm⁻¹ with the spectral resolution of 3 cm⁻¹ and integration time, 0.3 s for a single spectrum.

Hand specimens were crushed using a stainless steel jaw press and the chips were then ultrasonically washed in MilliQ H₂O to remove any seawater contamination. The Havre rhyolite was washed with weak HCl and water. The washed chips were subsequently dried and then powdered in an agate mill. Major element concentrations were determined on a Siemens^® SRS300 XRF at the University of Auckland, following standard techniques73 . Fresh glass was analyzed for the Havre rhyolite. A polished thin section was carbon coated and analyzed by a Cameca SX100 electron microprobe at Macquarie University. A defocused beam was used with an accelerating voltage of 15 kV and a beam current of 15 nA. Counting times of 10 s were used for both peak and background measurements. The analysis in Table 1 represents the average of 5 spots. Spectrometer calibration was achieved using the following standards: Jadeite (Na), Fayalite (Fe), kyanite (Al), olivine (Mg), chromite (Cr), spessartine garnet (Mn), orthoclase (K), wollastonite (Ca, Si) and TiO₂ (Ti).

A Cameca SX-100 electron microprobe was used for imaging and analysis of the chemical composition of laser-melted samples. Energy dispersive spectroscopy and backscattered electron imaging (BSE) were used for the characterization of sample homogeneity. Quantitative chemical analysis was performed by wavelength dispersive spectroscopy (WDS) using synthetic rare earth orthophosphate crystals for calibration standards for all rare earths except Y, for which synthetic Y₃Al₅O₁₂ (YAG) was used due to flux originated Pb contamination detected in YPO₄ standard.