Project Goals:

• Understand the kinematics and dynamics of extensional faulting during sea floor spreading
• Determine how extensional faults accommodate sea floor spreading in the absence of magmatic activity
• Understand strain localization mechanisms in mafic and ultramafic oceanic lithosphere
• Understand how extensional faulting is linked to fluid circulation in oceanic lithosphere
• Refine the theory of Plate Tectonics to explain newly observed geologic features on the sea floor

    Formation of new oceanic lithosphere at mid-ocean ridges is accomplished by a combination of magmatic activity and extensional faulting. Recent advances in sea floor sonar imaging and geophysical techniques has allowed scientists to determine the shape and internal structure of the ocean floor better than ever before. These studies have revealed morphologic and geologic structures at mid-ocean ridges that cannot be explained by the classical model of sea floor spreading. Like any good scientific theory, plate tectonics is currently being modified to incorporate these new observations. In particular, extensional faults at mid-ocean ridges may be far more complex than previously thought, and may actually the the sole mechanism to accommodate spreading during periods of little or no magma input to the shallow ridge axis, asymmetrical spreading, or during ridge migration. In short: if you want to understand plate tectonics, you have to spend at least part of the time looking beneath the oceans.

    I am studying faults at two sites along the Mid-Atlantic Ridge to meet these above goals, and make sure the theory of plate tectonics accurately explains the actual mechanics of our planet. Thus far, I have participated in two research cruises where we have used submersibles to map the sea floor and collect rock samples and a drill ship to collect core samples of oceanic lithosphere.

I visited Atlantis Massif  in fall of 2004 on a cruise of the RV Atlantis. We used the Alvin manned submersible and the remotely operated submersible ARGO II to map and sample the sea floor This cruise made several significant discoveries, including the Lost City hydrothermal vent field, which won the principle investigators considerable acclaim. More information on this cruise can be found here.

I visited the 15-20 Fracture Zone in the summer of 2003 on Ocean Drilling Program Leg 209. During this 8-week long cruise, we drilled 6 peridotite and gabbro exposures north and south of the transform fault.

Relevant Publications from Atlantis Massif:

Schroeder, T. , John, B, 2004, Strain localization on an oceanic detachment fault system, Atlantis Massif, 30°N, Mid-Atlantic Ridge: Geochemistry Geophysics Geosystems, v. 5, N. 11

Blackman, D. K., Karson, J.A., Kelley, D.S., Cann, J.R., Früh-Green, G.L., Gee, J.S., Hurst, S.D., John, B.E. Morgan, J., Nooner, S.L., Ross, D.K., Schroeder, T.J., and Williams, E.A., 2004, Geology of the Atlantis Massif (Mid-Atlantic Ridge, 30°N): Implications for the Evolution of an Ultramafic Oceanic Core Complex: Marine Geophysical Researches, v. 23, p. 443-469.

Schroeder, T. , John, B., and Frost, B.R., 2002, Geologic implications of seawater circulation through peridotite exposed at slow-spreading ridges, Geology, v. 30, p. 367-370.

The region shown in this image depicts the Mid-Atlantic Ridge axial valley (right side of image) and irregular bathymetry west of the ridge. Site 1275 is drilled on a domal "mega-mullion" hypothesized to be an oceanic core complex. East of this is a region of low relief, between zones of amplified abyssal hill morphology north and south.

Relevant Publications from 15-20 Fracture Zone:

Schroeder, T., Cheadle, M., Dick, H.B.J., Faul, U., Casey, J.F., Kelemen, P., 2007, “Non-volcanic seafloor spreading and corner-flow rotation accommodated by extensional faulting at 15°N on the Mid Atlantic Ridge: A structural synthesis of ODP Leg 209”, Geochemistry Geophysics Geosystems, v. 8, Q06015 DOI 10.1029/2006GC001567

Shipboard Scientific Party , 2003, Leg 209, Initial Reports; Drilling Mantle Peridotite along the Mid-Atlantic Ridge from 14° to 16°N, 6 May 2003–6 July 2003: http://www-odp.tamu.edu/publications/209_IR/209ir.htm Ocean Drilling Program Texas A&M University , College Station , TX

Shipboard Scientific Party, 2003, Leg 209 Preliminary Report Drilling Mantle Peridotite along the Mid-Atlantic Ridge from 14° to 16°N, 6 May 2003–6 July 2003: http://www-odp.tamu.edu/publications/prelim/209_prel/209PREL.PDF , Ocean Drilling Program Texas A&M University , College Station , TX