The Origin of Nanoscopic Grooving on
Vesicle Walls in Submarine Basaltic Glass:
Implications for Nanotechnology
Figure 7
Summary diagram showing the conceptual model explaining the initiation and formation of nanoscopic viscous fingering patterns on vesicle walls in mid-ocean ridge basaltic glass. (a) Schematic illustration depicting a putative 50 nm thick boundary layer around vesicle B, corresponding to the possible configuration of a previously existing, natural Hele-Shaw cell, which now contains frozen (or fossil) viscous fingers (V) of magmatic vapour. The thickness of this hypothetical boundary layer (50 nm) is estimated from the apparent depth of the fossil viscous fingers shown in (b). Although empirical evidence for the boundary layer has not yet been determined, it is predicted to comprise basaltic glass with slightly lower water contents than ambient values in surrounding glass. Note that in this example of ultrathin film surface layer viscous fingering on the vesicle wall, the Hele-Shaw cell essentially had imaginary walls, corresponding to the inner and outer reaches of the hypothetical dehydrated boundary layer. During viscous fingering, the more viscous fluid comprised hot basaltic glass that was probably near the glass transition temperature (600–C)—the less viscous invading fluid being magmatic vapour that was probably dominated by CO2. (b) Close-up SEI image (from Figure 2) showing the region of vesicle B for which a hypothetical boundary layer is illustrated in (a) (V—viscous fingers). (c) Illustration of pull-apart nanofracturing/fracturing/viscous fingering in a thin boundary layer predicted by numerical modelling of stress generation around some vesicles in glassy rocks (modified from [6]). The SEI image from (b) is located on this conceptual model. (d) Close-up SEI image of a portion of the vesicle wall from Figure 1, linking a tension gash (TG), and viscous fingers (V) to the conceptual model of their formation shown in (e). (e) Model for the stepwise initiation of viscous fingering in a 50 nm thick boundary layer of glass around a vesicle in a glassy pillow margin. denotes the components of traction normal to a surface, which define a tensile surface stress [26] that leads in this interpretation to the formation of a pull-apart viscous finger.
