(a)
(b)
(c)
(d)
(e)
(f)
Figure 17: Examples of a peculiar class of etch-tunnels at the glass-palagonite interface that formed either by (i) prolonged overetching of alpha-recoil track etch-tunnels (i.e., are overetched ARTETs or “OARTETs”) and/or (ii) by the advance of etch-tunnelling primarily through pressure solution (caused by increasing hydrostatic pressure through time: Figure 16). All images (a–f) are SEM (secondary electron) images, obtained from the freshly fractured surface of a basaltic glass “chip sample” from DSDP-418A-75-3[120–123]. Regardless of their origin, these etch-tunnels contain authigenic imogolite filaments within them (c, f) (similar in nature to the imogolite filaments found within ARTETs—see Figure 12), which seems to indicate possible links with alpha-recoil track etch-tunnelling. Note that the etch-tunnels in this region (a) actually occur along the same glass-palagonite interface and etch-tunnel zone shown in Figure 11 (which contains both FTETs and ARTETs) and occur nearby to some ARTETs (e.g., see ARTET at top right in (a)). Furthermore, some of the alteration features in the immediate vicinity of these tunnels are close to the same size as an alpha-recoil track (~120 nm) and are therefore interpreted as corroded or “infilled ARTETs” (see “IARTETs” at top right in (b) and at left in (e)). Although these comparatively large etch-tunnels (a, b, d, e) are closer in size to FTETs (~1-2 μm wide)—hinting at a possible “etched out” fission track cluster—they do not contain any authigenic platy smectite, which is observed ubiquitously within FTETs (see Figure 13). Therefore, these observations point to an origin that is different than fission track etch-tunnelling (i.e., (i) and/or (ii), above). Nevertheless, this peculiar class of etch-tunnels (OARTETs?) (b, d, e), is interpreted to be more or less equivalent to the variety of overetched microtunnels shown in Figure 7(e) that were imaged by transmitted light microscopy.