The chemical state and local environment of sulfur in basaltic glasses from the eastern Galapagos rift and quenched laboratory experiments have been investigated by synchrotron-radiation S K-edge X-ray absorption near-edge structure (XANES) spectroscopy, using an energy-selective fluorescence detector. We have also investigated sulfur in melts in the system 6NaAlSiO 4 -CaS-CaSO 4 quenched from 1500°C and various reference compounds, using conventional fluorescence yield and total-electron yield (TEY) recording modes. The S K-edge XANES spectrum of CaS dissolved in Na-aluminosilicate glass is dominated by a broad singlet edge-feature near 2475 eV, consistent with isolated SCa a coordination polyhedra in the melt, whereas that of quenched end-member CaSO 4 -bearing melt is similar to XANES spectra of crystalline sulfates. The linear correlation between relative XANES area and wt% content of sulfur has been used to estimate the content of sulfur in samples of lazurite (5.6-6.3 wt% by EPMA), scapolite-group minerals (0.4 wt%) and the basaltic glasses (0.04-0.15 wt%). The S K-edge XANES spectra of basaltic glasses synthesized under reducing (WM and IQF solid oxygen-buffer) conditions are dominated by a single broad absorption peak at 2470-2482 eV in combination with a weak peak or shoulder at 2470-2471 eV, and are reproduced by mixing XANES spectra of FeS and alkaline-earth monosulfides. The S K-edge XANES spectra for glasses from the eastern Galapagos rift are also dominated by S 2- , but one TEY spectrum shows possible thiosulfate and another, trace sulfate.
- Basaltic glass
- Chemical state of sulfur
- X-ray absorption near-edge structure (XANES) spectroscopy