The 23rd Nautile dive of the SMARTIES cruise, on August 15th, 2019, aimed at investigating the volcanic field located south of the main core complex and west of the last MAR oblique ridge axis. The main objective was to decipher the physical and morphological properties of lava flows exposed along the profile, which are critical observation to determine the original chemical and environmental conditions leading to volcanic activity. The dive took 5.5 hours at the sea bottom. We started at a depth of 3941 m, and left the seafloor at a depth of 3689 m. A series of extremely fresh glassy basalts were collected (14 samples), all showing cm thick glassy rind. The appearance of lava bodies is constant throughout the profile indicating a stability in the factors controlling the morphology of lavas as supply rate, viscosity and temperature. We observed well-preserved primary magmatic structures, as radial joints, corrugated surfaces, and different type of magmatic cracks e.g. spreading, contraction, transvers and tensional well on several outcrops of pillow flow. A major set of faults (oriented from N 120 to N150) clearly cross cut the magmatic bodies, as well as the later sedimentary deposits. These observations reveal that the magmatic field is located in an active tectonic area significantly affected by post magmatic tectonic events.

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By A. Soltanmohammadi