Grevemeyer, Ingo , Devey, Colin , Klaucke, Ingo and Lange, Dietrich (2021) Geological and geophysical characterization of transform offsets, TRANSFORMERS, Cruise No. M170, 11.01.2021 - 14.02.2021, Emden (Germany) - Emden (Germany). . METEOR-Berichte, M170 . Gutachterpanel Forschungsschiffe, Bonn, 32 pp. DOI 10.48433/cr_m170.

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Abstract

Fracture zones were recognized to be an integral part of the seabed long before plate
tectonics was established. Later, plate tectonics linked fracture zones to oceanic transform faults
(OTF), suggesting that they are the inactive and hence fossil trace of transforms. Yet, scientists
spend little time surveying them in much detail. Recent evidence suggests that the traditional
concept of transform faults as being conservative (non-accretionary) plate boundary faults might
be wrong. Instead, numerical modelling results suggest that transform faults seem to suffer from
extensional tectonics below their strike-slip surface fault zone, and a global compilation of
legacy bathymetric data suggest that ridge-transform intersections seem to be settings of
magmatic activity, modifying the lithosphere and burying the transform valley before it passes
into the fracture zone region. During M170 we tested those hypotheses by collecting a suite of
new data from the Oceanographer and Hayes transform faults offsetting the Mid-Atlantic Ridge
to the south of the Azores near 35°N and hence conducted a pilot study revealing the state-of-stress derived from micro-earthquakes and bathymetry as well as geological sampling to evaluate
magmatic and tectonic processes shaping transform faults. Preliminary analysis of 10-days of
seismicity data recorded at hydrophone stations showed 10-15 local earthquakes per day and
bathymetric data supports that ridge-transform intersections support indeed a second phase of
magmatic accretion.

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