Spatial and Temporal Patterns of Magmatic and Hydrothermal Activity Along the East Pacific Rise between 9°-10°N

M.H. Cormier *¹, S.C. Webb², W.R. Buck², S. Nooner², W. Crawford³, G. Applebee¹, & R.C. Holmes²

Corresponding author: CormierM@Missouri.edu
¹Dept. Geological Sciences, University of Missouri – Columbia, MO 65203
²Lamont-Doherty Earth Observatory, Columbia University, NY 10964
³Institut de Physique du Globe, Paris, France

Abstract:
Nineteen bottom pressure recorders have been deployed along the East between 9°-10°N since March 2007 to monitor vertical movement of the seafloor associated with magma movement. These will be recovered in December 2009. Vertical displacements of tens of centimeters are expected for either dike intrusion or sill deflation along the EPR. A combination of dike opening and sill deflation might lead to smaller, but likely detectable vertical deflections. The pressure sensor is a proven technology that has detected small (cm) to large (m) vertical motions on mid-ocean ridges. Numerical modeling of vertical deformation expected for dike intrusion and sill inflation/deflation cycles for EPR appropriate dimensions will be carried out to interpret the data collected.

As ancillary operations to the geodetic experiment, tow-yo profiling of water column properties was carried out continuously between 9°31’-10°04’N, when time permitted between deployments. Overall, these data highlight a pattern of intense and continuous hydrothermal plumes between 9°31’-10°02’N, within the broader “bull’s eye” area of this integrated study site. This is similar to the pattern that emerged from tow-yo profiles acquired soon after the 1991 eruption at 9°45’-51’N [Baker et al., EPSL 1994]. An hydrothermal plume between 9°58’N and 10°02’N, north of the site of the documented 1991 and 2006 eruptions, is significantly more vigorous in 2007 than it was 1991. Lava samples dredged at 10°01’N during the 2007 expedition are visually undistinguishable from samples collected from the 2006 lava flow, suggesting that a relatively recent eruption occurred north of the bull’s eye area. This interpretation may be supported by the pattern of seismicity detected south of the Clipperton transform fault within days of the 2006 eruption by the Autonomous Hydrophone Array [Dziak et al., G-cubed 2009]. In addition, the 2008 data reveals light attenuation within the bull’s eye area that are significantly lower than values measured soon after the 2006 eruption [Cowen et al., Eos Trans. 2007], and a plume height that is 100-140 m deeper overall, confirming the strong temporal connection between hydrothermal plumes and magmatic activity.

Keywords:
EPR ISS; eruption; crustal deformation; hydrothermal plume; along-axis variations;

Contribution to integration and synthesis:
The array of bottom pressure recorders is expected to detect any eruption or subsurface dike intrusion that occurred between 2007-2009 along this 110 km-long segment, and any positive identification of such events will be immediately released to the Ridge2000 community. This experiment will provide some needed context to interpret other geophysical, chemical, and biological data collected during that same time span.

Continued acquisition of tow-yo profiles as ancillary programs to scheduled cruises to the 9°N integrated study site would further our understanding of magmatic and hydrothermal cycles in some cost-effective manner, and effort will be done to carry some additional oned during the upcoming recovery expedition.