This 21st dive was carried out on August 13, 2019, in a transition zone located between, an expansion zone perpendicular to the direction of the ridge, to the South, an oblique expansion zone to the North.

We reached the seafloor at -4318 m at 10:44 UT on sediments. During the next 50 minutes we continued to move above the sediments, some well indurated and affected by normal faults. The first basalt flows then appeared, represented by lava pillows many of which were broken. Then we crossed several escarpments resulting from the action of recent faults. We were able to map a profile and sample basalts up the slopes. Along the studied profile, the area appeared very sedimented, with lava pillow flows interposed in the sediments. In particular, all peaks are covered with sediment containing pillow debris. The area did not reveal any active volcanism, but significant extensional tectonic activity. The basalts sampled delivered extremely fresh volcanic glass, suggesting that the faults are recent in age.

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The sediments being a bit monotonous, this dive also allowed us to observe the curious micro-organisms that populate these abyssal depths. We left the bottom at 15:52 UT, having traveled 3,647 km.

By. M. Seyler

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