Recent tectonic, magmatic, and hydrothermal activity on the East Pacific Rise between 17°S and 19°S: Submersible observations

Abstract

The objective of the Naudur cruise (December 1993) of the submersible Nautile was to study the interaction among magmatic, tectonic, and hydrothermal processes at a very fast spreading mid‐ocean ridge axis. Twenty‐three dives were completed, both along and across the axis, in four areas located between 17°10′ and 18°45′S on the East Pacific Rise. Rock, sulfides, water, and biological samples have been collected along each of the segments. Two main types of segments have been distinguished, characterized either by the predominance of present‐day volcanic activity or by predominant tectonic activity. Linked to both types of activity, 69 hydrothermal sites have been discovered and sampled. They comprise four types, interpreted as successive evolutionary stages. The first are shimmering water sites which occur immediately after the formation of lava lakes and are characterized by large surface area and poorly developed associated fauna. The second, in areas dominated by recent volcanic activity, have waters venting directly from lava fissures and more focused discharge areas through black smoker chimneys. The third stage is represented by more mature hydrothermal vents and deposits, along the faults bounding the eastern side of the axial graben in tectonic‐dominated areas. The associated fauna is well developed. The fourth stage corresponds to the reactivation of volcanic activity with lava flows, young black smokers, and diffuse venting associated with the faults bounding the axial graben. Fluids collected range from 200° to 340°C and show a wide variability in chemical and gas composition. Within each of the explored areas, evidence of recent volcanic activity has been observed.

Recent volcanic events and the distribution of hydrothermal venting at the Lucky Strike hydrothermal field, Mid‐Atlantic Ridge

“…[36] The Lucky Strike lava lake contains flat lavas and lava pillars similar to those observed at the axis of the intermediate and fast spreading ridges [Ballard, 1979;Francheteau et al, 1979;Auzende et al, 1996;Gregg and Chadwick, 1996;Gregg et al, 2000;Lagabrielle et al, 2001;Chadwick, 2003;Tanaka et al, 2007]. Lava pillars have also been reported at the Mid-Atlantic Ridge south of the Oceanographer transform [Bideau et al, 1998].…”

Community structure of mussel beds at deep-sea hydrothermal vents

“…comm.). The Oasis field is located on a lava flow that had 'young' characteristics in 1993; large areas of diffuse discharge without sessile animals and with a turbid, flocculent appearance (Fouquet et al 1994, Auzende et al 1996. The Oasis field corresponds to the northern 'L0' region of the Embley et al (1998) study, where, in 1995, 'Shinkai 6500' divers observed colonization of small, low-effusion-rate vents in what had been described as 'uncolonized areas of shimmering water' by 'Nautile' divers the previous year (Fouquet et al 1994).…”

Seismic and magnetic constraints on the structure of upper oceanic crust at fast and slow spreading ridges

“…This area has been extensively mapped [Scheirer et al, 1996], and was the focus of two submersible dive programs [Renard et al, 1985;Auzende et al, 1996], a detailed seismic refraction/reflection survey (TERA) , and the Mantle ELectromagnetic and Tomographic (MELT)…”