A Microkrystite from the Australasian Tektite/Microtektite Strewn FieldOPEN ACCESS 

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Matteo Del Rio, Luigi Folco, Matteo Masotta, Ana Černok, Enrico Mugnaioli

MAPS, Version of Record online: 25 September 2026

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“Microkrystites are glassy impact spherules. They contain primary crystallites carrying information on the physical and chemical conditions prevailing during vaporization, melting, and ejection in large impact cratering events. We report on the geochemistry and mineralogy down to nanometer scale of the first microkrystite (ODP1144A,14) from the Australasian tektite/microtektite strewn field. It is a dark-gray, opaque, 160 × 210 μm prolate spheroid, recovered from the microtektite layer in the Ocean Drilling Program Hole 1144A in the South China Sea. The microkrystite shows a micro-glomeroporphyritic texture consisting of clusters of skeletal ferropseudobrookite (Fe2+0.7,Fe3+0.3)Σ=1(Ti1.7Fe3+0.3)Σ=2O5 crystals (~70 area%) set in a silicate glassy matrix. The latter features nanoscale Fe-Ti liquid-immiscibility textures and Si-rich inclusions composed of quartz, lechatelierite, and shock-produced coesite. Coesite confirms an impact origin of the microkrystite. Major and trace element compositions of the glassy matrix and of the spherules accreted onto the particle surface match those of Australasian microtektites, firmly linking ODP1144A,14 to the Australasian strewn field. Vesicles and partially digested lechatelierite inclusions indicate formation as an impact-melt droplet rather than a vapor condensate. We suggest that the non-silicate part of the ODP1144A,14 microkrystite derived from an immiscible Fe–Ti-rich melt batch (about the size of a droplet) produced by impact melting at T > 1400°C of target Fe-Ti oxides (commonly found in the shocked target ejecta fragments associated with microtektites in the same stratigraphic horizon) that could not fully homogenize with the bulk silicate microtektite precursor melt under the transient disequilibrium conditions that are characteristic of impact melting and fragmentation during high-velocity ejection. We suggest that the involvement of target Fe-Ti oxides during impact melting may have contributed to the Cr-rich, Ni-poor terrestrial mafic component observed in some Australasian tektites and microtektites. This provides further support to earlier assessment of the dual origin, dominantly chondritic and lesser terrestrial, of the mafic component in Australasian tektites and microtektites.”

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