HR: 1340h
AN: B13A-0167    [Abstracts]
TI: Burying Tectonic Strain Under Lava Flows at the East Pacific Rise (9\deg N 26'-58'N)
AU: * Fornari, D
EM: dfornari@whoi.edu
AF: Geology and Geophysics, WHOI, Woods Hole, MA 02543 United States
AU: Escartin, J
EM: escartin@ipgp.jussieu.fr
AF: Geosciences Marines (CNRS/IPGP), 4 Place Jussieu (case 89), Paris, 75252 France
AU: Soule, A
EM: ssoule@whoi.edu
AF: Geology and Geophysics, WHOI, Woods Hole, MA 02543 United States
AU: Schouten, H
EM: hschouten@whoi.edu
AF: Geology and Geophysics, WHOI, Woods Hole, MA 02543 United States
AU: Tivey, M
EM: mtivey@whoi.edu
AF: Geology and Geophysics, WHOI, Woods Hole, MA 02543 United States
AU: Ferrini, V
EM: ferrini@ldeo.columbia.edu
AF: LDEO, P.O. Box 1000 61 Route 9W, Palisades, NY 10964 United States
AB: High resolution, deep tow sonar images of the EPR at 9\deg N 26'-58'N in combination with high resolution near-bottom bathymetry provide constraints on the interaction between faulting and magmatism. Areas of the seafloor recently resurfaced by lava flows can be recognized by their high acoustic reflectivity compared to that of older, sedimented seafloor. The off-axis limit of the 'recent' volcanic seafloor is highly variable (between 1.5 and 5 km from the axis) and is controlled primarily by fault scarps that dam lava flows originating at the axial summit trough (AST). We have quantified the deformation intensity (density of fissures and faults) and characterized the fault scarp height both on 'recent' and 'old' (i.e., sedimented) seafloor. For seafloor of the same spreading (calculated from the distance to the AST and the spreading rate), the 'old' seafloor shows more tectonic deformation than the repaved seafloor: fault and fissure density is 5 times greater, fault scarps are 2-4 times higher, and tectonic strain along selected transects is 4 times greater. In all cases inward facing faults account for 70% of the faults. These results demonstrate that almost all the tectonic strain and deformation (80% or more) is systematically buried by volcanic flows in the vicinity of the axis. Faults that develop sufficient scarp heights so as not to be buried by flows dam subsequent lava flows at distances of 1 to 5 km from the AST, and effectively limit the length of lava flows. Near-axis tectonism appears to play a previously overseen role in the build up of the extrusive oceanic crustal later. Burial of 80% or more of the faults and grabens implies an efficient, fault assisted subsidence of volcanics near the AST. The limitation of lava flow length by fault scarps indicates the thickening of Layer 2A away from the aixs may be controlled by the fault nucleation and growth of faults, and not solely by the accummulation or successive lava flows.
DE: 8414 Eruption mechanisms
DE: 8010 Fractures and faults
DE: 5475 Tectonics (8149)
DE: 5480 Volcanism (8450)
DE: 3035 Midocean ridge processes
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting