Critical testing of potential cellular structures within microtubes in 145Â Ma volcanic glass from the Argo Abyssal Plain

Elemental enrichments and depletions in three chemically distinct regions (glass, alteration rim, and tube interior) provide further insights into microtube formation mechanisms. Alteration rims have sharply defined edges, are about 0.1 μm wide independent of microtube diameter, and are primarily composed of Si, Al, O ± Ti. The tube interiors are depleted in Si and Al, and most other elements (Ca, Mg, Na, Mn) relative to fresh glass but K and Fe may be enriched. There is no evidence for depletion of elements in the glass immediately exterior to the alteration rim. This favours a mechanism whereby microtubes grow by increasing in length, rather than increasing in diameter. In this model protons are the major agent of glass alteration and the supply of protons and the kinetics of the formation of the Si-Al alteration rim control the diameter of the microtubes.