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Kinematics and geometry of active detachment faulting beneath the Trans-Atlantic Geotraverse (TAG) hydrothermal field on the Mid-Atlantic Ridge

Brian J. deMartin^*,1, Robert A. Sohn^,2, Juan Pablo Canales² and Susan E. Humphris²

¹ Massachusetts Institute of Technology–Woods Hole Oceanographic Institution Joint Program in Oceanography, Cambridge, Massachusetts 02139, USA
² Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA

Newly acquired seismic refraction and microearthquake data from the Trans-Atlantic Geotraverse (TAG) segment of the Mid-Atlantic Ridge at 26°N reveal for the first time the geometry and seismic character of an active oceanic detachment fault. Hypocenters from 19,232 microearthquakes observed during an eight month ocean bottom seismometer deployment form an 15-km-long, dome-shaped fault surface that penetrates to depths >7 km below the seafloor on a steeply dipping (70°) interface. A tomographic model of compressional-wave velocities demonstrates that lower crustal rocks are being exhumed in the detachment footwall, which appears to roll over to a shallow dip of 20° ± 5° and become aseismic at a depth of 3 km. Outboard of the detachment the exhumed lithosphere is deformed by ridge-parallel, antithetical normal faulting. Our results suggest that hydrothermal fluids at the TAG field exploit the detachment fault to extract heat from a region near the crust-mantle interface over long periods of time.

Key Words: detachment faults • hydrothermal vents • Mid-Atlantic ridge • tectonics • earthquakes • seismic profiles

This article has been cited by other articles:

				C. J. Lissenberg, M. Rioux, N. Shimizu, S. A. Bowring, and C. Mevel Zircon Dating of Oceanic Crustal Accretion Science, February 20, 2009; 323(5917): 1048 - 1050. [Abstract] [Full Text] [PDF]