Sulfide geochronology along the Northern Equatorial Mid-Atlantic Ridge

Abstract

Hydrothermal processes and seafloor massive sulfide (SMS) deposits have different characteristics at fast and slow spreading mid-ocean ridges. One such parameter is the age of a SMS deposit, which differs by 1–2 orders of magnitude between the fast spreading East Pacific Rise (EPR) and the slow spreading Mid-Atlantic Ridge (MAR). The large collection of SMS samples dated from the 18 hydrothermal fields of the northern equatorial part of the Mid-Atlantic Ridge (194 samples) demonstrates a relatively old average age of hydrothermal fields here (~66ka) with the oldest one estimated as ca. 223ka (Peterburgskoye field). Based on geochronological data it was confirmed that hydrothermal discharge has an episodic character: active and inactive periods of the SMS formation alternate. The distribution of events at all hydrothermal fields demonstrates that maximum activity occurred at 38–35, 30–20, and 8–2ka and increased with time. Based on statistical analyses, dating variations can be explained as a superposition of several periods of activity with the duration of ~15, 10 and 5ka.Relationship between the age and distance from the axial rift zone as well as between the age and aerial distribution is different for SMS deposits hosted by basalts and by gabbro-peridotites depending on their geological setting on the particular MAR segment. This difference can be explained by a variety of hydrothermal processes determined by “tectonic” or “magmatic” segment evolution and symmetrical or asymmetrical mode of accretion (Escartin et al., 2008).