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International Research
therefore considered to be newer than the NNW-SSE trending
structures.
The morphology in the portion between the lava plain and the
western margin is sheet flows visible in thinly sediments. The
lava flow morphology is similar to that found in #1088. In the
western end of the dive near the western wall of the median
valley, the seafloor is composed of pillows and lava tubes. In
visual observation, heavy sedimentation is obvious compared
to the seafloor in #1088, thus the seafloor in #1090 is considered
slightly old. However as a result of the sub-bottom profiler
observation, thickness of the sedimentary layers is estimated to
be less than several tens of centimeters. Therefore, the sedimentation
of western margins of the median valley is thinner than
that of the eastern margin in dive #1089.
4. Sample descriptions
4.1. Rock samples
Basaltic rock samples were collected at total of 22 stations in
the three dives (Fig. 2). The rock samples are folded crust of
sheet flows or pillow lava fragments. Samples obtained from
#1088, particularly those from the axial portion of the median
valley, have glass rings and almost no manganese coating (