Crossing the transform fault: a second dive

On the 30th of July the objective of the dive was to investigate the damaged zone of the Romanche transform fault. The fault is located inside a deep and wide valley, and the dive profile started at a depth of 5573 m. The dive crossed the transform fault from South to North, then a second crossing back to the South America plate. The age contrast across the fault at the dive location is about 30 million years. This was the second dive dedicated to the sampling and imaging of the active transform fault.

The seafloor was quite smooth and covered with sediments. No outcrop with in situ rocks was observed but debris with blocks of different dimensions and a few larger blocks. We were however able to observe particular structures in the sediment (lineations and small faults) that have the same orientation of the Romanche transform and that testify the continuous tectonic activity of the main fault.

The rocks sampled at the transform area were mainly plagioclase harzburgites and plagioclase peridotites weakly deformed.This second dive through the transform fault repeated the profile made during the sixth dive of the cruise, located further west and all the lithologies sampled resemble those recovered during this previous dive.

By A. Cipriani