Oxidation Dynamics and their Effects on Texture and Magnetic Response in Remelted and Quenched Submarine Basaltic Glass

As part of an experimental and observational study of the magnetic response of submarine basaltic glass (SBG), we have examined -- using ion backscattering spectrometry (RBS), transmission and scanning electron microscopy (TEM; SEM), energy-dispersive X-ray spectrometry (EDS) and surface X-ray diffraction (XRD) -- the textures wrought by the controlled oxidation of glasses prepared by the controlled-environment remelting and quenching of natural SBG. Initial compositions with 9 < FeO*(wt%) < 12 were melted at 1700K with the oxygen fugacity buffered at fayalite-magnetite-quartz (FMQ); melts were cooled at rates in the range 0.08-2.30 K s-1 in air and, separately, in FMQ atmospheres; oxidation experiments involved reheating polished pieces of this reprocessed glass in dry air to temperatures of 425K, 875K or 1000K for times ranging from ~10 to >1000 h. (The glass transition temperature of the reprocessed glass is ~950K.) RBS demonstrates unequivocally that the dynamics of oxidation involves the outward motion of network- modifying cations. Highest temperature oxidation results in formation of nm-"Ým-scale ferrites (close to pure magnetite) on the free surface, devoid of ionic Ti; lowest-temperature oxidation sees formation of a Na- enriched phase on the surface. The highest-T oxidation specimens have magnetizations elevated by one-to- two orders of magnitude relative to the as-quenched material. Specimens are being evaluated for internal structural/textural change accompanying the internal chemical changes associated with the oxidation dynamic.