Coesite in a Muong Nong‐type tektite from Muong Phin, Laos: Description, formation, and survival

1Billy P. Glass,2Luigi Folco,2Matteo Masotta,2,3Fabrizio Campanale
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13433]
1Department of Geological Sciences, University of Delaware, Newark, Delaware, 19716 USA
2Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy
3Center for Nanotechnology Innovation@NEST, Istituto Italiano di Tecnologia (IIT), Piazza San Silvestro 12, 56127 Pisa, Italy
Published by arrangement with John Wiley & Sons

We examined 16 white opaque inclusions exposed on two polished slices of a Muong Nong‐type Australasian tektite from Muong Phin, Laos. The inclusions usually consist of a core, surrounded by a froth layer, and a quartz neoblast layer. The cores are composed primarily of a mixture of silica glass, coesite, and quartz in varying proportions. A thin (up to ~4 μm) layer of SiO2‐poor glass enriched in FeO, MgO, CaO, Al2O3, and TiO2 is observed as a bright halo in backscattered electron images around the quartz neoblasts and in places contains μm‐sized crystals, which may be Fe,Mg‐rich spinel. The distribution and textural relationships between the coesite‐bearing inclusions and the tektite matrix point to an in situ formation of the coesite due to an impact, rather than to infall, from a nearby impact, into tektite melt produced by the aerial burst of a bolide. The quartz neoblasts probably formed by crystallization of silica melt squeezed out of the inclusion core during the development of the froth layer. The bright halo may be the result of silica diffusing from the adjacent tektite melt into the growing quartz neoblasts. We propose that the survival of coesite was possible due to the froth layer that acted as a heat sink during bubble expansion and then as a thermal insulator.

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