Ocean crust geochemistry: Construction and hydrothermal alteration of oceanic crust
Project Manager/Lead Scientist: Debra Stakes

This project is a renewal of the Ocean Crust Geochemistry project. The goal of this effort is to constrain the relationship of magmatism and hydrothermalism in the construction of ocean crust. It includes field and geochemical studies of the upper crust around mid-ocean ridges where new ROV observations suggest that combined hydrothermalism and magmatism are present several kilometers from the spreading axis. A new emphasis in this project will be to incorporate isotopic and collaborative biological studies to search for clues of microbial processes.

Within the Mendocino Transform Zone (MTZ), intact slabs of ocean crust transferred from the Gorda Plate to the Pacific Plate by the northward progression of the Mendocino Triple Junction (MTJ) are exposed along the Gorda Escarpment. Rock age and chemistry reveals both the tectonic and magmatic processes inherent in ocean crust created near a triple point. The uplift of the escarpment has also induced basin-wide flow of methane-charged pore fluids from the organic rich  Miocene-
Pliocene sediments of the Pacific Plate. The northward flow and venting of these warm pore fluids has produced methane seeps with two sparsely populated chemosynthetic communities and authigenic carbonates with methane-hydrate isotopic signatures. Continuing effort for the MTZ sample suite will be detailed analyses of rock alteration (hydrothermal and microbial) on samples already collected. 

Chimney samples from the southern Guaymas basin will be analyzed for mineral assemblages and growth history, complemented by bulk chemistry and stable isotopic studies (oxygen, carbon, sulfur).

Ongoing study of the Cleft Segment of the southernmost Juan de Fuca Ridge is addressing the construction and alteration of oceanic layer two. Field observations from past  ROV dives are the basis of a model for the role of off-axis volcanism in the construction of the uppermost layers of oceanic crust.

The Endeavour Segment of the northern Juan de Fuca ridge is both seismically more active and tectonically more dismembered than the Cleft Segment. There is evidence of recent off-axis volcanic events that apparently reset the robust axial hydrothermal system. Rocks collected there in 2002 will be subjected to geochemistry and geochronological studies. This area will offer an important comparison to the Cleft segment in testing the hypothesis of the importance off-axis volcanism. The  geochemistry study will also provide a useful complement to the Keck studies in documenting off-axis volcanism and hydrothermal venting.