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

Abstract

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.

Revisiting the paleomagnetism of Muong Nong layered tektites: Implications for their formation process

“…Muong Nong tektites are also characterized, with respect to standard splashform australasites, by (1) a higher volatile content (water, noble gases, etc. ; see Koeberl 1992;Beran and Koeberl 1997;Mizote et al 2003); (2) the pressure of gas bubbles within the atmospheric range, while splashforms bubble pressure estimates suggest solidification outside the atmosphere (Mizote et al 2003;Z ak et al 2019); (3) the preservation of crystalline inclusions of coesite, cristobalite, zircon, and magnetite (Kleinman 1969;Glass and Barlow 1979;Cavosie et al 2018;Krizova et al 2019;Masotta et al 2020) indicative of lower peak temperatures.…”

Obsidian and mafic volcanic glasses from the Philippines and Vietnam found in the Paris Museum Australasian tektite collection

“…Zr versus Sr plot for the studied pseudotektites (circles) as well as reference outcrops from the Philippines (diamonds; see Table 3); data for the Australasian tektites (black squares; both Muong Nong and splash form types) from the literature (Amare & Koeberl, 2006; Chapman & Schreiber, 1969; Masotta et al., 2020; Mizera et al., 2016; Son & Koeberl, 2005; Žak et al., 2019) are shown for comparison. [Color figure can be viewed at wileyonlinelibrary.com] …”

“…Total alkali silica (TAS) diagram (after Le Maitre, 2002) for pseudotektites (circles) based on ICP-AES (or electron micro-probe analyzer for sample 2200; see Tables1 and 2), and for geological references for the Philippine glasses afterReepmeyer et al (2011; green diamonds). Data for the Australasian tektites (black diamonds; both Muong Nong and splash form types) from the literature(Amare & Koeberl, 2006;Chapman & Schreiber, 1969;Masotta et al, 2020;Mizera et al, 2016;Son & Koeberl, 2005;Zak et al, 2019), as well as high Na/K australites (red triangles afterChapman & Schreiber, 1969) are shown for comparison. (Color figure can be viewed at wileyonlinelibrary.com.…”

Textures Induced by the Coesite‐Stishovite Transition and Implications for the Visibility of the X‐Discontinuity

“…Because the MGC analysis of coesite was performed directly after the transformation from quartz, the random orientation of the crystals is consistent with the reconstructive nature of the quartz‐coesite transformation that should not induce any inherited LPO in the daughter crystals (Tolédano & Dmitriev, 1996). Recent studies have shown that in rare cases, such as during impacts, a crystallographic parent‐daughter relation can be preserved throughout the quartz‐coesite transition (Campanale et al., 2019; Glass et al., 2020; Masotta et al., 2020). However, the exact conditions required for such coherent orientation relationships, as well as the corresponding transformation mechanism, remain unclear.…”

“…Recent studies have shown that in rare cases, such as during impacts, a crystallographic parent-daughter relation can be preserved throughout the quartz-coesite transition (Campanale et al, 2019;Glass et al, 2020;Masotta et al, 2020). However, the exact conditions required for such coherent orientation relationships, as well as the corresponding transformation mechanism, remain unclear.…”