Structure and chemistry of TECHNO encrustations

Using as a starting point the results giving 'traditional' growth rates as determined by the decrease of radioelements (part I) and the hypothesis of rapid formation, the different mineralogical, structure and chemical characteristics of the sample have been studied to try to understand the possible mode of formation of this encrustation. A rapid formation would account for (1) the very peculiar structure of the sample composed of oriented botryoids and the bundle-like structure of the outermost oxide layer; (2) the fact that this sample represents a substitution of a preexisting hyaloclastite; (3) the different chemical gradients, mainly iron, thorium and uranium; (4) the fact that this sample which cannot have been maintained at the sediment-water interface by bioturbation is not covered by a great thickness of sediments. On the other hand, an unsolved problem remains: Why different radionuclides used for dating give growth rates of the same order of magnitude and different 'exposition ages'.