Observers: William Ryan(transcript) and Mario Aigner-Torres (transcript)
Pilot: Dudley Foster
Launch: 18° 34.90' S, 113° 24.90 W
Summary: Dive Alivin 3347 completed thirteen zig-zag
transects across the so-called "Auzende Flow" within
the axial depression (graben or valley) working north from -18°
34.7' S to -18° 33.5' S (for an along-axis distance of 4 km).
The first three transects at the south end of the explored corridor
encountered numerous crustal slivers bounded by faults. The slivers
deepen from the east rim into the valley floor, whereas northward
the valley floor is more or less one intact surface that is broad,
flat and cut by a single or sometimes by two N-S running deep
fissures (clefts) repeatedly visited on sequential transects.
Age-relationships: The terrain outside the valley (either directly on its rim or in the case of the first transect, extending several hundred meters down the east flank of the axial high) is everywhere pillow lava characterized by elongated pillows and tubes with a pronounced orientation indicating a flow direction downslope and away from the valley. This "valley exterior" terrain is old (age 3.0 to 2.5). An identical pillowed terrain is observed on the surfaces of the individual crustal slivers with in the southern part of the valley itself. This mostly pillowed and subordinately lobated terrain in the center of the southern valley becomes somewhat younger and reaches a minimum of age 2.0. Where the valley floor is broad, locally smooth and dips ever-so slightly northward (starting around -18° 34.3' S) it is extensively surfaced with sheet flows (wavy, jumbled, striated and "billiard table" smooth) of an even still younger age 1.5. The valley floor also deepens gradually the south from this mid point. However to the south the surficial valley floor flooding flows are of the lobate rather than sheet-type. These southern lobates are, as best as can be ascertained from visual observation, the same apparent age (1.5) as the northern sheets. The very youngest flows (age 1.0) are very limited in areal extent and are found only in the floor of the clefts (age 1.0). Scattered talus aprons are shed onto the edges of the valley floor from the bounding walls. Nevertheless, for the most part, the talus that makes up steep ramps at the base of the east and west bounding walls is older than the last valley floor flooding events and is overlapped by their flows.
Tectonics: The bounding walls of the axial valley are clearly of displacement origin, though they also reveal the subsequent effects of mass wasting. As near vertical cliffs they expose the now buried interior substrate of the former axial high that we presume to have predated the formation of the broad, deep valley (speculation). This substrate is almost exclusively comprised of pillow lavas exposed in the cliffs as round and radially cracked cross-sections of either pillow heads, trunks or tubes. The truncated pillows appear in the wall in horizontal layering (looks like bedded rock) even though they consists of individual appendages of the flows. Very little of the wall is massive rock. The bounding wall is on several occasions a narrow sliver (2-4 m deep perpendicular to the cliff face and ten or more meters in height) detached along a vertical joint that forms an opening which widens upwards. The cliff edge on one transect consists of at least three of these slivers in succession pealed off and tilting ever so slightly into the valley. Every time it could be inspected the top of a sliver is the same heavily sedimented terrain as that found on the topmost rim and on the flank of the axial high exterior to the valley floor (age 2.5 to 3.0). Glass has spalled from the rocks exposed in the opening joints and it has accumulated on steep scree surfaces made of sand to pea-sized glittering fragments that further down near the base of the cliffs pass into duller pebble, cobble, boulder and even car-sized blocks of talus. Round pillow trucks and heads are common as allochtonous blocks in the valley edge talus. On one occasion a sliver of the wall was observed to have fallen inward onto the valley floor so that its pillowed cap dipped 45° towards the valley center and its smooth joint surface along which it had separated from the wall now dipped 45° back towards escarpment. Fissures on valley floor slice into terrain that is either not vertically offset on either side of the cut, or at the fissure steps downward or upward on the scale of 1 to 2 meters. These fissures and the deeper and wider ones called clefts provide excellent exposures of the valley floor substrate. Such fissures and clefts are commonly but not everywhere associated with facets stained white by presumable hydrothermal exhalations. Staining was more prevalent in cracked pillow lavas near the base of the valley-bounding walls, less in the valley floor lobates and very rare in the sheet flows except in the immediate vicinity of the valley floor clefts. It is all together absent outside the valley (rim or flank of the axial high). Around these clefts the submersible induced turbulence scattered into the water the "spaghetti" worms that colonize the rims and uppermost walls of the clefts.
Stratigraphic relationships of the lavas: Several excellent exposures on cliffs and in the walls of fissures revealed the cross-sections of "giant" tubes one or more meters in diameter with a clearly visible exterior skin (<10 cm. in thickness). This skin displays radial patterns like those of a pillow but radiate from a far away center so that the fabric on the truncated skin consisted of a parallel indentations and ridges perpendicular to the circumference of the tube (looks like megascopic sparry calcite). The tubes were not ideally rounded, but squashed horizontally and with the skin folded to accommodated the plastic deformation (the crenulated skin was uncracked). More than once we saw the "giant" tubes filled or partly filled with uniformly thin (2 cm thickness) horizontally-bedded flows that in vertical exposure look like a cut through a stack of Neco Wafers". These are not bathtub rings on the walls or pillows of a lava pond. Where one could look down on the top flat surface of these thin flows within the "giant" tubes, it was very flat and dull with no signs of reflective glass. The tubes that were partly occupied by these thin flows either had voids at their tops, or were filled the rest of the way by what looked like welded talus. The talus here was tabular and did not contain fragments of pillows but pieces that resembled roof rock or the skin of the tubes itself. The tops of the tubes lay just below the seafloor (the rim of the exposure) and were covered either by pillows or lobates that were only one or two flows in thickness. The exposure between the "giant" tubes was exclusively pillow terrain seen in round cross-section and with their typical radial fracture patterns showing that they had been severed by the fissuring or faulting process. Lobates were conspicuously absent in the lavas between and below the tubes in the exposures we observed and when present were only the surficial capping flow or two at the top of the escarpment. More than once we clearly observed the lobate to have dripped down the face of the exposure as if it were a flow contemporaneous with the fissuring/faulting event. The descending tongues were never more than 0.5m in length and did not reach the base of the fissure or fault escarpment. In the context that we saw them as the stratigraphically highest flows, the lobate lava in cross-section was lens shaped, more or less flat on the bottom, convex upward at the top with 3-5 cm. thick thin walls (skin) and typically hollow (empty) with drips hanging from the bottom of their roofs. Thus we may infer that they were both cut by the faulting/fissuring and emptied by pouring into the crack formed. The "giant" tubes were only seen in vertical cross-sections exposed in the floor of the valley by small relief faulting and fissuring. We did not report any such tubes from the more vast exposure we looked at from the valley bounding walls. However, it is important to remark that we were almost always rapidly ascending these walls, so the opportunity to stop and hunt for such tubes in the valley wall context did not present itself. When exploring the valley floor where the sheet flows lay adjacent to lobate flows, we typically saw the tongues of the lobates flow out onto the sheets. The lavas in this context seemed to be of the same relative age. The sheet flows rapidly changed their morphology in a spatial sense of a few meters from wavy, to jumbled, to striated, to "billiard table" smooth. However, almost invariably the "billiard table" smooth sheets were cracked into large polygon slabs and slightly sagged in very shallow (<0.5m) depressions five or more meters in breadth. The white staining in cracks of presumed hydrothermal origin was never associated with an aureole on the sediment adjacent to the crack and no color change in the sediment cover was observed towards a stained crack.
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