Identifying probable signatures of hydrothermal activity from the Carlsberg ridge sediments using rock magnetic properties

The Carlsberg Ridge (CR) is a slow-spreading ridge occurs along divergent plate boundary, with the reports of three active and one extinct hydrothermal vent sites. For the present study eight spade cores (SCs) were collected from the CR, of which three are in the vicinity of Tianxiu hydrothermal field and one on the ridge flank. The hydrothermal sites are known to be associated with metalliferous sediments with Fe being the one of the dominant element. We measured rock magnetic properties of sediments that depend on iron bearing minerals, along with X-ray diffractometry (XRD), and microscopic observations to distinguish metalliferous sediments, that may be associated with the active/extinct hydrothermal activity at the CR. Magnetic susceptibility (χ_lf) of sediments ranges between 1.3 and 37.1 x10^-8 m³kg^-1. Low χ_lf signatures suggesting low metalliferous sediments are observed on flank and two cores from the ridge valley indicating, the absence of hydrothermal activity. Whereas sediments closer to the Tianxiu hydrothermal vent field are associated with high χ_lf, signifying higher metalliferous sediments and are also having high satuaration isothermal remanent magnetization (SIRM), hard isothermal remanent magnetization (HIRM), and low anhysteretic remanent magnetic susceptibility (χ_ARM)/SIRM, coarse stable single domain (SSD)  and fine SSD & mixture grains characteristics. Two more spade cores ~ 250 km south of the Tianxiu vent field also showed similar signatures indicating new active/relict site/sites in the vicinity. Identifying/locating metalliferous hydrothermal sediment/sites along extensive Mid Ocean Ridge (MOR) is expensive and time-consuming; rock magnetic could be a non-destructive method to shortlist the areas for detailed studies.