Abstract EANA2026-250

Paleoarchean pillow lavas from the Barberton Greenstone Belt, South Africa, preserve titanite-bearing tubular microtextures in altered basaltic glass. These structures have been interpreted as traces of microbial alteration in ancient oceanic crust, yet their origin remains debated because low-grade metamorphism and later fluid flow can also produce or modify mineral textures and carbonaceous signals. This makes the Barberton samples a useful test case for assessing biosignatures in altered volcanic rocks, with relevance to early Earth studies and Mars sample-return science. Here we examine the same type of candidate microtextures using optical microscopy, Raman, NanoSIMS, TEM and atom probe tomography (APT). Optical observations show that segmented tubular structures are hosted in a chlorite-rich matrix and filled by titanite. Raman spectra identify titanite, chlorite and carbonaceous material, and suggest distinct alteration domains at tubular margins, in the chlorite matrix and along fractures. NanoSIMS maps show coupled 12C, 12C14N and 32S signals along selected tubular margins. Carbon also occurs as isolated spots in the chlorite matrix and along fractures. TEM resolves nanoscale titanite–chlorite intergrowths at the margins of the microtextures. APT records C-, CN- and Mn-rich domains at titanite–chlorite interfaces, together with carbon-bearing signals within chlorite interlayers. The data distinguish four carbon occurrences in the sample: carbon on tubular margins, carbon dispersed in the chlorite matrix, fracture-related carbon and carbon hosted in chlorite interlayers. The tubular-margin carbon has the strongest link with N- and Mn-bearing signals. This association is consistent with an organic–mineral interface and may record redox reactions involving Fe and Mn in altered basaltic glass. Carbon in the matrix, fractures and chlorite interlayers is more consistent with later carbon mobility during fluid infiltration or metamorphic recrystallization. The Barberton microtextures cannot be judged from morphology alone. Their origin must be tested through the nanoscale relation among carbon, nitrogen, sulfur, Mn-bearing phases, titanite and chlorite. This correlative approach provides a way to assess candidate biosignatures in ancient volcanic crust and offers criteria for future astrobiology missions seeking life traces in altered basaltic materials on Mars.