Evidence for subsolidus quartz-coesite transformation in impact ejecta from the Australasian tektite strewn field

Campanale, Fabrizio; Mugnaioli, Enrico; Folco, Luigi; Gemmi, Mauro; Lee, Martin; Daly, Luke; Glass, B. P.

doi:10.1016/j.gca.2019.08.014

Cited by 10 publications

(26 citation statements)

References 55 publications

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“…The first two models envisage coesite formation during shock unloading (i.e., when the pressure release path passes via the coesite stability field) through crystallization from a silica shock melt (Langenhorst 2003;Chen et al 2010;Fazio et al 2017) or subsolidus nucleation from highly densified diaplectic silica glass (St€ ahle et al 2008). A third model involves the formation of coesite through direct subsolidus transformation from quartz, facilitated by localized reverberation (attenuation and amplification) of the compression shock wave due to discontinuities in the target (Kieffer et al 1976;Folco et al 2018;Campanale et al 2019).…”

Section: Formation Of the Coesitementioning

confidence: 99%

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

Glass

Folco

Masotta

et al. 2020

Meteorit & Planetary Scien

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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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Section: Formation Of the Coesitementioning

confidence: 99%

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

Glass

Folco

Masotta

et al. 2020

Meteorit & Planetary Scien

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“…Its formation conditions have been a debated issue since its discovery in nature by Chao et al 1 . Three models of coesite formation have been proposed: (1) crystallisation during decompression from silica melt with short-range order and silicon in fourfold coordination 2 – 7 or (2) crystallisation in solid-state condition from diaplectic silica glass 8 ; (3) direct solid-state quartz-to-coesite transformation in thermodynamically non-equilibrium conditions 9 – 11 . The models (1) and (2) are essentially based on the study of non-porous target rocks and single quartz crystals, while model (3) derives from the study of porous sandstones.…”

Section: Introductionmentioning

confidence: 99%

The formation of impact coesite

Campanale

Mugnaioli

Gemmi

et al. 2021

Sci Rep

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Coesite in impact rocks is traditionally considered a retrograde product formed during pressure release by the crystallisation of an amorphous phase (either silica melt or diaplectic glass). Recently, the detailed microscopic and crystallographic study of impact ejecta from Kamil crater and the Australasian tektite strewn field pointed in turn to a different coesite formation pathway, through subsolidus quartz-to-coesite transformation. We report here further evidence documenting the formation of coesite directly from quartz. In Kamil ejecta we found sub-micrometric single-coesite-crystals that represent the first crystallization seeds of coesite. Coesite in Australasian samples show instead well-developed subeuhedral crystals, growing at the expenses of hosting quartz and postdating PDF deformation. Coesite (010) plane is most often parallel to quartz {10–11} plane family, supporting the formation of coesite through a topotactic transformation. Such reaction is facilitated by the presence of pre-existing and shock-induced discontinuities in the target. Shock wave reverberations can provide pressure and time conditions for coesite nucleation and growth. Because discontinuities occur in both porous and non-porous rocks and the coesite formation mechanism appears similar for small and large impacts, we infer that the proposed subsolidus transformation model is valid for all types of quartz-bearing target rocks.

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“…6 CEREGE, Aix-Marseille University, CNRS, INRA, IRD, Aix-en-Provence, France. 7 Department of Earth Sciences, University of Delaware, Newark, DE, USA. 8 Center for Nanotechnology Innovation@NEST, Istituto Italiano di Tecnologia (IIT), Pisa, Italy.…”

Section: Openmentioning

confidence: 99%

“…In the Australasian tektite strewn field, coesite was found as microcrystalline grains in partly melted mineral inclusions within impact melt glasses (namely tektites 9,10 ) and in shocked ejecta found in the Australasian microtektite layer 7,11 . Muong Nong (MN) tektites constitute one of the three tektite types associated with the Australasian strewn field and the only one where coesite was occasionally found 9,10 .…”

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confidence: 99%

“…The preservation of coesite as a metastable phase in shocked rocks that experienced peak pressures and temperatures much beyond its stability field (i.e., pressures of 3-10 GPa and temperatures below 2700 °C) represents a controversial issue 2 . For this reason, different mechanisms of coesite formation have been proposed, including coesite crystallization from an impact silica melt during shock unloading [3][4][5] , subsolidus nucleation from highly densified diaplectic silica glass 6 and direct subsolidus quartz-coesite transition upon shockwave reverberation 2,7 . Regardless of the formation mechanism, the kinetic of the coesite → quartz transformation determines the possibility of coesite survival in a transient high-pressure and high-temperature regime (e.g.…”

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

Masotta

Peres

Folco

et al. 2020

Sci Rep

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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.

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Evidence for subsolidus quartz-coesite transformation in impact ejecta from the Australasian tektite strewn field

Cited by 10 publications

References 55 publications

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

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

The formation of impact coesite

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

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