Lucky Strike seamount: Implications for the emplacement and rifting of segment‐centered volcanoes at slow spreading mid‐ocean ridges

Abstract

The history of emplacement, tectonic evolution, and dismemberment of a central volcano within the rift valley of the slow spreading Mid-Atlantic Ridge at the Lucky Strike Segment is deduced using near-bottom sidescan sonar imagery and visual observations. Volcano emplacement is rapid (<1 Myr), associated with focused eruptions, and with effusion rates feeding lava flows that bury tectonic features developed prior to and during volcano construction. This volcanic phase likely requires efficient melt pooling and a long-lived crustal magma chamber as a melt source. A reduction in melt supply triggers formation of an axial graben rifting the central volcano, and the onset of seafloor spreading may eventually split it. At Lucky Strike, this results in two modes of crustal construction. Eruptions and tectonic activity focus at a narrow graben that bisects the central volcano and contains the youngest lava flows, accumulating a thick layer of extrusives. Away from the volcano summit, deformation and volcanic emplacement is distributed throughout the rift valley floor, lacking a clear locus of accretion and deformation. Volcanic emplacement on the rift floor is characterized by axial volcanic ridges fed by dikes that propagate from the central axial magma chamber. The mode of rapid volcano construction and subsequent rifting observed at the Lucky Strike seamount is common at other central volcanoes along the global mid-ocean ridge system.

Magmatic plumbing at Lucky Strike volcano based on olivine‐hosted melt inclusion compositions

“…Numerous geophysical studies have been carried out on the Lucky Strike segment. At the segment scale, there is a ''bull's-eye'' mantle Bouguer gravity low, suggesting focused upwelling and melt delivery from the mantle to the center of the ridge segment [Detrick et al, 1995;Thibaud et al, 1998;Cannat et al, 1999;Escart ın et al, 2001]. Crustal thickness varies from 7-7.5 km at the segment center to 5-6 km at segment ends [Seher et al, 2010], consistent with focused melt delivery to the segment center.…”

“…The segment is 70 km in length, has a mean depth of 2580 m, and is bound by nontransform offsets [Parson et al, 2000]. At the middle of the Lucky Strike segment, a central volcano rises to 1660 m water depth [Cannat et al, 1999;Escart ın et al, 2001]. The central volcano contains a central depression, infilled by lava, surrounded by three highs that correspond to rifted volcanic cones [Fouquet et al, 1998;Humphris et al, 2002;Escart ın et al, 2014] (Figure 1).…”

“…At the middle of the Lucky Strike segment, a central volcano rises to 1660 m water depth [Cannat et al, 1999;Escart ın et al, 2001]. The central volcano contains a central depression, infilled by lava, surrounded by three highs that correspond to rifted volcanic cones [Fouquet et al, 1998;Humphris et al, 2002;Escart ın et al, 2014] (Figure 1). One of the largest active basalt hosted, deep-sea hydrothermal vent fields is located at the summit of this central volcano [Langmuir et al, 1997;Ondr eas et al, 2009;Barreyre et al, 2012].…”

Melt inclusion constraints on petrogenesis of the 2014–2015 Holuhraun eruption, Iceland

“…Alternatively, fissure eruptions along rift zones may be driven by pressurization of lower crustal magma reservoirs and the injection of subvertical dykes towards the surface, with associated movement on caldera ring faults resulting from the concentration of dyke-induced stress fields around pre-existing faults and/or shallow magma chambers (e.g., Gudmundsson 1995;Gudmundsson et al 2014). These models have been discussed extensively with respect to volcano-tectonic episodes for volcanic edifices including Kilauea, Hawaii (Ryan 1988;Baker and Amelung 2012); the Afar region of Ethiopia (Wright et al 2006;Jeir et al 2009;Ebinger et al 2010); and mid-ocean ridge segments (e.g., Fialko and Rubin 1998;Dziak et al 1995;Escartín et al 2014).…”

Hydrothermal activity along the slow-spreading Lucky Strike ridge segment (Mid-Atlantic Ridge): Distribution, heatflux, and geological controls

“…These segments typically 53 develop ridge-parallel normal faults on both flanks, and thick crust at their center 54 indicating melt-focusing along-axis. As in the case of the Lucky Strike segment, sustained 55 volcanismmay lead to the development of central volcanoes (Escartín et al, 2014). The 56 slow-spreading Lucky Strike segment is unique in that it has been extensively studied 57 during more than two decades, following the discovery of the Lucky Strike hydrothermal 58 field, from hereon referred to as the Main Lucky Strike hydrothermal field (MLSHF), 59 located at its segment center and at the summit of the central volcano (Langmuir et al,60 portion of the Lucky Strike segment.…”