Geotectonic setting of hydrothermal activity on the summit of Lucky Strike Seamount (37°17′N, Mid‐Atlantic Ridge)

Abstract

[1] We have investigated the relations between volcanic, tectonic, and hydrothermal activity on Lucky Strike Seamount (37°17 0 N, Mid-Atlantic Ridge) using a nested survey strategy involving collection of data from different deep-sea mapping systems. The highly tectonized seamount summit consists of three volcanic cones surrounding a relatively flat depression with a young lava lake in its center. Hydrothermal activity is focused mainly within the summit depression with most of the vents located proximal to the lava lake. Isolated active and inactive chimneys and mounds are widespread throughout the summit depression and occur on both volcanic (pillow lava) and hydrothermal (sulfide rubble and hydrothermally cemented breccias) substrates. The large volume of sulfide rubble, together with the nature of the sulfide structures, indicates that hydrothermal activity has been episodic but ongoing for a long period of time (hundreds to thousands of years). On the basis of the distribution of hydrothermal deposits, we propose a model of alternation between tectonic and volcanic control on hydrothermalism at Lucky Strike Seamount. Midsegment melt focusing produces a spatially and temporally stable heat source that sustains focused high-temperature hydrothermal activity over long time periods. During periods of amagmatic extension, active faulting within the summit depression provides multiple, near-surface fluid flow pathways for discharge of high-temperature fluids and widespread deposition of massive sulfides. During eruptive events, rapid effusion of very hot lava creates a lava lake and hyaloclastite deposits. The new sheet flows form a cap on the hydrothermal system, and fluid upflow is reorganized. Discharge of high-temperature fluids is restricted to isolated sites with relatively high permeability, for example, the edges of the lava lake. Much of the upwelling hydrothermal fluid pools in the subsurface, conductively cools, and mixes with entrained seawater before discharging as widespread low-temperature diffuse flow. Hyaloclastites become cemented, further augmenting the sealing of the system. Present-day activity at Lucky Strike Seamount represents this locally volcanically controlled phase of activity, despite the segment as a whole being dominantly amagmatic.

Identification of the magnetization low of the Lucky Strike hydrothermal vent using surface magnetic data

“…To the east, the volcano summit has a half circular shape, with three small volcanic cones around a central depression, that hosts a lava lake [Fouquet et al, 1995]. The hydrothermal field of Lucky Strike was discovered here (37°17 0 N, 32°16.5 0 W, compare Figure 1) during dredging on the FAZAR mission [Langmuir et al, 1993], and the active focused or diffusive hydrothermal activity is located mainly around the lava lake [Fouquet et al, 1995;Humphris et al, 2002].…”

“…Sonar images and seafloor geology [Ondreas et al, 1997, Scheirer et al, 2000Humphris et al, 2002] have revealed that the midvalley floor is largely amagmatic in character. During the FLORES mission [Fouquet and the FLORES Scientific Team, 1997] the presence of mantle exposures was verified by dredging of serpentinites at the base of the SW inside corner high.…”

“…[40] A second magnetization low is located in a flat platform between the Lucky Strike central volcano eastern flank and the elevated summit area of the lava lake [Humphris et al, 2002]. DSL120 images and bathymetry reveal a small depression, punctuated by a set of highly discontinuous acoustic shadows pointing for debris and mass wasting.…”

“…[39] The magnetic low that encompasses the Lucky Strike hydrothermal field, the lava lake and related hydrothermal precipitates tapping the regions around it [Humphris et al, 2002], shows spatial correlation with the surface expressions of hydrothermal activity. This favors an interpretation where chemical alteration induced by focalized hydrothermal up flow is the main mechanism for the demagnetization process.…”

Rapid colonisation by nematodes on organic and inorganic substrata deployed at the deep-sea Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge)

“…As hot fluid venting is transient, hydrothermal vent sites have ephemeral lifespans ranging from years (e.g. HV 9°50′ N at the East Pacific Rise (EPR); Shank et al 1998;Lutz et al 2008) to decades or, exceptionally, centuries [e.g., the Mid-Atlantic Ridge, (MAR); Humphris et al 2002]. Distances between HV fields are variable (up to hundreds of kilometres; Murton et al 1994;German et al Communicated by P. Martinez Arbizu 1996).…”