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Background Information >>

East Pacific Rise
East Pacific Rise - taken from WHOI--Dive and Discover and slightly altered

The overlapping spreading center at 9°03’ N is a highly perturbed and variable area. This variability holds the promise of revealing important linkages between sub-ridge melt distribution and variations in lava composition, geology, and hydrothermal activity.

Recent seismic and tomographic imaging of the sub-ridge upper mantle and crust beneath the OSC provides an unprecedented view of the distribution of melt at depth. It is within this context that we are undertaking a detailed geochemical, geological, geophysical, and hydrothermal study of this second-order ridge discontinuity.

Our study will consist of a nested survey of DSL-120A side-scan sonar to obtain regional coverage of the geologic characteristics of the overlapping spreading center, and Jason II to obtain continuous photographic and sampling coverage (rock and hydrothermal).

ARAD Map
Bathymetry of the 9°03’N area of the EPR, after Kent et al. (2000).

Our goals are to:

1) Identify and characterize the extent of lava flows, and faulting and fissuring on both limbs of the ridge as well as within the overlap basin.

2) Obtain a substantial suite of lavas from flows on each limb of the OSC and the overlap basin to explore spatial and temporal variations in composition and link these to both the geologic and seismic results. In addition, we will determine ages of eruption for a subset of samples by U-series dating techniques.

3) Survey for evidence of hydrothermal activity, using the CTD deployed on the Jason II sled and photographic images.

3-D view of melt sill beneath eastern limb of the OSC, looking northeast from the overlap basin
3-D view of melt sill beneath eastern limb of the OSC, looking northeast from the overlap basin (Kent et al.; 2000). Orange and blue-green hues denote the magma chamber reservoir at depth; red and blue hues denote the seafloor above (cut-away)

Our overall goal is to identify variations in geology, geochemistry and hydrothermal activity that correlate with along-axis changes in melt lens and mantle melt parameters, and thus be able to tie deep crustal and upper mantle processes to their surface manifestations.