Geoscience Reference
In-Depth Information
4.7
Dive 6K#610
This dive aimed to confirm the northern limit of serpentinite exposure. The landed
point was located on the basin floor along 29°8.22'N, where the middle terrace is
not evident, and the submersible first climbed upslope to the east. Debris apron
between the basin floor and 3,270 mbsl contained blocks of andesitic tuff breccia
and limestone. Outcrop at 3,270 mbsl consisted of hornblende andesite lava. From
this point, the dive route was set as iso-contour traverse around 3,270-3,230 mbsl
toward the south, along which jointed lava was occasionally exposed on the steep
slope covered by volcaniclastic debris and semi-consolidated mud. Floats (?) of
altered and amygdaloidal olivine basaltic andesite were collected at 29°7.68'N
(3,230 mbsl) at the northern end of the mid-slope terrace.
4.8
Dive 6K#1064
This route was approximately the same site as, and crossing the track of dive
6K#609. The slope deeper than 3,340 mbsl was covered by debris and mud, from
which blocks correlative to Miocene turbidite were collected (Fig.
5h
). Outcrops of
schistose serpentinite, each of which was separated from others by mud-covered
talus, occurred between 3,340 and 3,260 mbsl. At 3,238-3,234 mbsl occurred a bed
of semi-consolidated mudstone, whose surface was covered by thin Fe-Mn oxide.
The bed was parallel to the slope surface. Between 3,234 and 3,228 mbsl, the slope
was covered by presumable landslide debris of rectangular blocks and very loose
rock masses of basaltic volcanic rocks. The slope between 3,202 m and the off-
bottom point (3,176 m) was covered by mud and partly by semi-consolidated mud.
4.9
Dive 6K#1065
This dive route obliquely climbed the slope from the landed point near the base
of slope apron at 29°6.7'N (3,453 mbsl) heading ESE, crossing the #575 track,
where foliated rocks were not sampled by the previous dive. The first outcrop,
which appeared at 3,381 mbsl above a mud-covered rubbly apron, consisted of
schistose serpentinite with pronounced foliation moderately dipping to northeast.
Schistose serpentinite also occurred at 3,361-3,365 mbsl, where foliation moder-
ately dips to southeast, and at 3,272-3,228 mbsl, where it showed apparently
weaker foliation on surfaces. Floats of pumice tuff and coral limestone (Fig.
5g
)
were collected on the steep and mud-covered talus among these outcrops. Partly
fractured massive serpentinite was exposed between 3,218 and 3,204 mbsl. Here
the submersible headed south moving to a deeper part of the slope. Apparently
massive serpentinite was exposed between 3,267 and 3,236 mbsl. At 3,236 mbsl,
a schistose serpentinite was collected from a fractured outcrop. The outcrop of
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