3D X-ray tomographic analysis reveals how coesite is preserved in Muong Nong-type tektites

Matteo Masotta (1) , Stefano Peres (1) , Luigi Folco (1) , Lucia Mancini (2, 3) , Pierre Rochette (4) , Billy Glass (5) , Fabrizio Campanale (1) , Nicolas Gueninchault (6) , Francesco Radica (7) , Sounthone Singsoupho (8) , Enrique Navarro (9)

1 University of Pisa - Università di Pisa
2 Elettra Sincrotrone Trieste
3 Skane University Hospital [Lund]
4 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
5 University of Delaware [Newark]
6 Zeiss Research Microscopy Solutions
7 ROMA TRE - Università degli Studi Roma Tre = Roma Tre University
8 National University of Laos
9 Universidad Nacional Autónoma de Managua [Nicaragua]

Muong Nong-type (MN) tektites are a layered type of tektite associated to the Australasian strewn field, the youngest (790 kyr) and largest on Earth. In some MN tektites, coesite is observed in association with relict quartz and silica glass within inclusions surrounded by a froth layer. The formation of coesite-bearing frothy inclusions is here investigated through a 3D textural multiscale analysis of the vesicles contained in a MN tektite sample, combined with compositional and spectroscopic data. The vesicle size distribution testifies to a post-shock decompression that induced melting and extensive vesiculation in the tektite melt. Compared to free vesicles, nucleated homogeneously in the tektite melt, froth vesicles nucleated heterogeneously on relict quartz surfaces at the margins of coesite-bearing inclusions. The rapid detachment of the froth vesicles and prompt reactivation of the nucleation site favoured the packing of vesicles and the formation of the froth structure. Vesicle relaxation time scales suggest that the vesiculation process lasted few seconds. The formation of the froth layer was instrumental for the preservation of coesite, promoting quenching of the inclusion core through the subtraction of heat during froth expansion, thereby physically insulating the inclusion until the final quench of the tektite melt.

Domaines: Sciences de la Terre

Matteo Masotta, Stefano Peres, Luigi Folco, Lucia Mancini, Pierre Rochette, et al.. 3D X-ray tomographic analysis reveals how coesite is preserved in Muong Nong-type tektites. Scientific Reports, 2020, 10 (1), ⟨10.1038/s41598-020-76727-6⟩. ⟨hal-03146969⟩