Hydrothermal venting along Earth's fastest spreading center: East Pacific Rise, 27.5°–32.3°

Abstract

we conducted detailed mapping and sampling of hydrothermal plumes along six segments of Earth's fasting spreading mid-ocean ridge, 27.5°-32.3°S on the East Pacific Rise. We compared the distribution and chemistry of hydrothermal plumes to geological indicators of long-term (spreading rate) and moderate-term (ridge inflation) variations in magmatic budget. In this large-offset, propagating rift setting, these geological indices span virtually the entire range found along fast spreading ridges worldwide. Hydrothermal plumes overlaid $60% of the length of superfast (>130 km/Myr) spreading axis surveyed and defined at least 14 separate vent fields. We observed no plumes over the slower spreading propagating segments. Finer-scale variations in the magmatic budget also correlated with hydrothermal activity, as the location of the five most intense plumes corresponded to subsegment peaks in ridge inflation. Along the entire ridge crest, the more inflated a ridge location the more likely it was to be overlain by a hydrothermal plume. Plume chemistry mostly reflected discharge from mature vent fields apparently unperturbed by magmatic activity within the last few years. Plume samples with high volatile/metal ratios, generally indicating recent seafloor volcanism, were scarce. Along-axis trends in both volatile ( 3 He; CH 4 ; ÁpH, a proxy for CO 2 ; and particulate S) and nonvolatile (Fe, Mn) species showed a first-order agreement with the trend of ridge inflation. Nevertheless, a broad correspondence between the concentration of volatile species in plumes and geological proxies of magma supply identifies a pervasive magmatic imprint on this superfast spreading group of ridge segments.

Distal transport of dissolved hydrothermal iron in the deep South Pacific Ocean

“…Elevated dFe concentrations near sites of hydrothermal venting have previously been observed in the abyssal Pacific (13,14,32). What makes the South Pacific dFe data of this study truly remarkable, however, is that they are sampled from locations hundreds to thousands of kilometers from the nearest known vent source, and they still demonstrate elevated dFe concentrations of ∼1.0-1.5 nmol/kg.…”

Metalliferous sediments from the H.M.S. Challenger voyage (1872–1876)

“…The seafloor spreading rates at the active plate boundaries in this region are currently the fastest on the planet ($15 cm/yr; Hey et al, 2004). This unusual tectonic setting creates a high rate of tectonic and volcanic activity giving rise to unusual magmatic-hydrothermal systems (Baker et al, 2002;Hey et al, 2004). The extremely high hydrothermal activity in this region has resulted in the development of the largest field of metalliferous sediments in the Ocean (Gurvich, 2006).…”

Seismic and gravitational studies of melting in the mantle's thermal boundary layers

“…The permeability structure of the crust and subsequent hydrothermal venting at fast spreading ridges is thought to be controlled by diking events from a steady-state axial magma chamber . This results in small, relatively short-lived hydrothermal vents whose heat flux increases following magmatic eruptions, as observed at the fast-spreading East Pacific Rise (EPR) [Haymon et al, , 1993Baker et al, 2002]. In contrast, control of the permeability structure of crust at slow spreading ridges has been attributed to extension-driven faulting and downward propagation of a cracking front into the lower crust where either no magma chamber is present or small, deep, pockets of melt occur .…”