XAFS study on the Zr local structures in tektites and natural glasses

Abstract

The local structures of tektites and natural glasses were studied by Zr K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements in order to obtain quantitative data on the Zr-O (bonding) distances and coordination numbers for the glasses. Zr 4+ ions have different coordination environments. The structure of glass (tektite, impact-related glass, fulgurite, and volcanic glasses) is affected by the temperature during the glass-formation process. Differences in the formation processes for natural glasses result in different local structures for the zirconium ions.All tektites can be classified as being of the same type and as having 7-fold coordination Zr ions. The Zr-O distances in tektite glasses are 2.198-2.215 Å, and their XANES spectra are similar, too. Impact-related glasses can be classified into different types and are formed under different physical and geological processes at the impact event. Volcanic glasses, impact-related glasses, and fulgurite glasses have several local Zr structures with 6-and 7-fold coordinated Zr ions. It can thus be concluded that local structures of Zr in natural glasses are closely related to the formation temperature and quenching conditions of the glasses. The Zr XAFS spectra of natural glasses can be used to identify the naturalglasses.

Significant Zr isotope variations in single zircon grains recording magma evolution history

“…Such zoning patterns indicate the preferential incorporation of light Zr isotopes into zircon (i.e., α < 1). Our finding is consistent with the first-order theoretical prediction where higher coordination-number lattices will be enriched in lighter isotopes, since in zircon, Zr has eightfold coordination (36), while in the melt it is generally found with sixfold coordination (37,38). This is also consistent with the α of 0.9995 inferred from bulk analyses of the Hekla volcanic rocks, where rhyolites (SiO 2 >65 wt%) show elevated δ 94 Zr values with reduced Zr contents (21).…”

XAFS study of Zr in Cretaceous–Tertiary boundary clays from Stevns Klint

“…The XANES spectra of Zr for volcanic glasses are comparatively similar to that for SrZrO 3 . The pattern is clearly different from those observed in typical Zr minerals (Mountjoy et al, 2000;Tobase et al, 2015). Additionally, those for K-T clays are also similar to those for obsidian and tektite.…”

“…The Zr-O distance, coordination number and RDF of K-T boundary clays are similar to rhyolitic volcanic glasses. The Zr-O distance and RDF for other natural glasses were presented in the Tobase et al (2015).…”

“…It should be concluded that Zr in the sedimentary rocks maintains the information on quench history at meteorite impact as comparing with other natural glass (Tobase et al, 2015). The possibility of large meteorite impact may be able to be judged by the Zr local structure investigation.…”

“…Zr K-edge XANES spectra of crystal phases have various kinds of patterns (Mountjoy et al, 2000). Additionally, XANES spectra of zirconium in impact-related glasses have various kind of information about local structure (Tobase et al, 2015). Zirconium should be useful probe for obtaining information on the local structures of crystalline phases, non-crystalline phases and formation process of K-T boundary clays.…”