BY:Dr. Nick Hayman
When: Friday, January 23, 2009 10:30 a.m. to 11:30 a.m.
Where: Seminar Room 1.603, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758
Host: Gail Christeson, UTIG
The escarpments that bound the Pito Deep Rift (northeastern Easter microplate) expose in situ upper oceanic crust that was accreted ~3 m.y. ago at the superfast-spreading (~142 mm/yr, full rate) Southeast Pacific Rise (SEPR). Samples and images of these escarpments were taken during transects utilizing the manned submersible Alvin and remotely operated vehicle Jason II. Mapping with a “deformation intensity scale” reveals that the sheeted dike complex and the base of the lavas contain ~meter-wide fault zones surrounded by fractured ‘damage zones’. Samples from these fault and damage zones have microstructures and compositions that developed over multiple increments of deformation and hydrothermal fluid flow in the subaxial environment of the SEPR. Some subaxial deformation increments were likely linked with violent discharge events associated with fluid pressure fluctuations and mineral sealing within the fault zones. Other increments were linked with the influx of relatively fresh seawater. The observations from the Pito Deep Rift are best explained by one of two currently competing models for axial hydrothermal fluid circulation, namely the “planar-crack” models with intermittent mineral sealing, and along-axis recharge of the hydrothermal system. Once spread from the ridge axis, the faults were probably not active, and damage zones likely played a more significant role in axial-flank and off-axis crustal permeability, arguably the most important component in crustal cooling.