Abstract
The Australasian tektite strewn field, the largest known on Earth, extends ~13,000 km from Southeast Asia to Antarctica. Previous studies have relied largely on bulk geochemical analyses, which cannot resolve particle-scale processes associated with impact-plume formation and ejecta transport. Here we report, to our knowledge, the first integrated microparticle- and nanoparticle-scale investigation of tektites across the Australasian strewn field. We document quenched micrometer-scale spherules and metallic particles attached to or embedded within freshly fractured interior glass, including specimens whose exterior surfaces were removed before crushing. Electron microscopy was combined with single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS) to characterize more than 175,000 individual nanoparticles, including over 10,000 containing platinum-group elements (PGEs), from seven regions spanning >7,000 km. The metallic particles and spherules include Fe-, Ni-, and Cu-rich metals, oxides, sulfides, and aluminosilicate phases. Some spherules are vesicular or compound, and, to our knowledge, discrete Ni-Cu-rich metallic particles have not previously been documented within Australasian tektite glass. Quartz grains exhibiting progressive melting and vesicular SiO₂-rich domains are consistent with intense heating and possible silica volatilization at ~1900–2200 °C. PGE-bearing nanoparticle mass distributions and inter-element relationships are broadly similar among regions, while bulk multi-element patterns also show strong compositional coherence, suggesting that these characteristics were established before long-range transport. In contrast, recovered nanoparticle abundance and summed PGE mass vary geographically and generally decline toward distal parts of the strewn field, although Thailand and central Australia depart from a simple monotonic distance trend. Several non-PGE metal nanoparticle populations show distinct regional distributions, indicating that different elements were not transported or retained uniformly across the strewn field. Single-particle Ir/Fe and Pt/Fe ratios differ markedly from average crustal reference values and overlap broad ranges reported for cometary particles, refractory metal nuggets, micrometeorites, and iron meteorites. These overlaps are consistent with, but do not prove, incorporation of extraterrestrial metal and are not diagnostic of a specific impactor class. Hydrocode simulations indicate that multi-kilometer-scale impactors can generate high-velocity, strongly downrange ejecta under shallow-impact conditions, consistent with the first-order transport requirements of the Australasian strewn field.