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Recent investigations of modern oceanic crust along the rifted walls of the Hess Deep Rift [Francheteau et al., 1990; Francheteau et al., 1992; Karson et al., 1992; Karson et al., 2002a] have provided a new perspective on the internal structure of fast-spread crust and by inference the processes attending accretion at spreading centers like the East Pacific Rise.

These studies have shown that the structural architecture and geochemistry of fast-spread oceanic crust is far more complex than current tectonic models imply. Most recently, a 30-km section of the north wall of the Hess Deep Rift was surveyed with a combination of DSL-120 side-scan sonar, digital mosaic surveys with the ROV Argo II, and Alvin dives [Karson et al., 2002a]. The program demonstrated the feasibility of this multi-scale mapping approach in a single cruise and that major escarpments on the seafloor provide important “tectonic windows” into the structure and composition of the upper oceanic crust.


Pito Deep

In January 2005, we plan to use a similar approach of nested scale sampling and analyses to investigate the structure and composition of EPR-generated crust exposed at Pito Deep. The crust at Pito Deep accreted at a faster spreading rate than that exposed at Hess Deep. Previous studies of Pito Deep, using the French submersible Nautile, showed a section of upper ocean crust extending from gabbro at the base, passing upward into sheeted dikes, and overlain by lavas. We plan to map these exposures to define the structural geometry, igneous composition, hydrothermal alteration and magnetic properties of these upper crustal units in order to provide important constraints on the nature of accretion along superfast-spreading ridges like the southern EPR. In addition to the effects of differing spreading rates, we expect the results of this study of oceanic crust generated along a segment center will differ from those observed at the relatively cool, segment-end setting represented by Hess Deep. These data and information will be used to test current models of oceanic crust generation and refine our understanding of ocean floor processes in space and time.

Topography of the Pito Deep
(from Hey et al., 2002)

Lauching submersible Alvin from the R/V Atlantis
(courtesy Woods Hole Oceanographic Institution)

Working inside Alvin

Collecting orientation data on the ocean floor using the Geocompass. Note Alvin's two mechanical arms (left and right) and sample basket (bottom).



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