Geochemistry of ocean crust
Lead Scientist: Debra Stakes
Project Manager: Karen Salamy

This project has two primary components: 1) the study of lower oceanic crust as exposed along fracture zones and at modern and ancient ridge-transform intersections; 2) detailed mapping of lavas and sulfides from a modern mid-ocean ridge in support of future instrument deployments. A third component is the adaptation of the MBARI rock coring system to ROV Tiburon. 

The crystalline rocks of the lower ocean crust record the magmatic processes that can only be inferred from the overlying volcanics. The rocks also preserve the deformational history as the rocks cool and move away from the mid-ocean ridge. High temperature deformation is the footprint of deep, near-axis faults while broken rocks welded with low temperature minerals may reflect a sub-crustal hydrofracture event. The cumulative effects of hydrothermal circulation over print these structural and textural changes. These crystalline rocks thus provide the critical ground-truth required to extend mid-ocean ridge models into four dimensions. Systematic sampling of crystalline rocks from the lower oceanic crust has historically been hampered by the small number of exposures, the limits of submersibles to adequately image a vertical wall; and the difficulties of collecting fresh, high quality samples. Many of these technical problems have been addressed in the development of Tiburon, with its superior station-keeping and imaging capabilities. 

We propose the study of several critical targets that are within the range of the ROV Tiburon.

1) A comparison of two ridge-transform intersections: The Blanco-southern Juan de Fuca system and the Davidson Seamount (a 23 my failed rift)-Moro Fracture Zone system. This effort will be in collaboration with Alice' Davis.

2) Examination of crystalline rocks from the Mendocino Fracture Zone. This effort includes both the Mendocino Ridge and the Gorda Escarpment and is in collaboration with Marty Fisk, Bob Duncan and Anne Trehu.

3) Continuation of the NSF supported study of gabbros from the Atlantis Bank. Southwest Indian Ridge.

These studies of crystalline rocks will be supplemented by detailed sampling of the Southern Juan de Fuca Ridge to develop a magmatic stratigraphy for the site of the proposed Ridge Observatory Experiment. The mapping effort on the southern Juan de Fuca Ridge includes both North and South Cleft segments and will be in collaboration with Mike Perfit and Matt Smith, who have already collected a significant suite of samples. It will be based upon the high resolution EM300 and DSL120 maps.