The analysis of magnetic properties and results of paleomagnetic investigation of serpentinites from the Gorringe Ridge (Azores-Gibraltar fracture zone)

A comparision of magnetic properties of two collections of serpentinites of Gorringe Ridge is carried out. The antigorite serpentinites were drilled b y the research ship "Bavenit" while the lizardite-chrysotile ones were drag ged during cruise XII of the research ship "Vityaz". The dragged samples de monstrated high magnetic hardness due to presumably submicron size of ferri magnetic grains. This conclusion is confirmed by direct electron microscope observations. The lizardite-chrysotile serpentinites have substantialy les ser hardness with typical size of magnetite grains at several microns thoug h sometimes quite coarse grains with size up to several tens microns are ob served. Indeed such difference of the magnetic properties of the collection s is not accidental and is dure to their different stages of serpentinizati on. NRM of drilled samples showed extremly inhomogeneous distribution of bo th value and direction, at the same time all the magnetic characteristics w ere quite homogeneous. Such a behavior of the NRM is attributed to drilling remanence imparted by coarse grains in Some parts of the core during drill ing. After selection of samples and magnetic cleaning of the rest ones, two modes of paleoinclination were found out grouping around 0 and -17 degrees . A possible explanation suggests the existence of two stages of serpentini zation during tectonic and magmatic evolution of the ridge.