HR: 11:05h
AN: T22E-04 INVITED    [Abstracts]
TI: The effect of fault segmentation on the dynamics of fast-slipping oceanic transform faults
AU: * Gregg, P M
EM: pgregg@whoi.edu
AF: MIT/WHOI Joint Program, Dept. Geology and Geophysics MS 24, Woods Hole, MA 02543, United States
AU: Behn, M D
EM: mbehn@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. Geology and Geophysics MS 22, Woods Hole, MA 02543, United States
AU: Lin, J
EM: jlin@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. Geology and Geophysics MS 22, Woods Hole, MA 02543, United States
AU: Grove, T L
EM: tlgrove@mit.edu
AF: Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 77 Massachusetts Avenue, Cambridge, MA 02139, United States
AU: Montési, L G
EM: montesi@umd.edu
AF: University of Maryland College Park, Department of Geology, College Park, MD 20742, United States
AB: The majority of oceanic transform faults (OTFs) systems along the fast-spreading equatorial East Pacific Rise are segmented into two or more strike-slip fault strands as a result of plate motion reorganization. Fresh basaltic lava sampled from these locations (e.g., the Siqueiros and Garrett OTFs) indicate that active crustal accretion is occurring within these transform systems. New Residual Mantle Bouguer gravity Anomalies (RMBA) calculated along fast-slipping OTFs are found to be more negative than the RMBA values along adjacent ridge segments. One possible explanation for these observations is enhanced magmatic upwelling and crustal accretion at intra- transform spreading centers (ITSC) and within the transform valley of the fast-slipping OTFs. In this study, we examine two end-member 3-D thermal models (constant viscosity rheology versus visco-plastic rheology) to explore mantle flow and melt extraction beneath segmented transform faults. Melt fraction is calculated using the parameterized fractional melting model of Kinzler and Grove (JGR, 1992a, 1992b, and 1993), and the fractional crystallization models of Yang et al. (Cont. Min. Pet., 1996). We evaluate the sensitivity of these models to various parameters including transform fault geometry, mantle potential temperature, and initial mantle composition. Preliminary results for a 100 km-long transform fault, slipping at 100 mm/yr, segmented by a single 10 km-long ITSC indicate that incorporating a visco-plastic rheology results in an approximately 35 percent decrease in the brittle fault area (< 600°C isotherm) compared to a constant viscosity model. Assuming upward melt migration along the base of the lithosphere, we find that crustal production is enhanced at ITSC by 1–1.5 km compared to the adjacent ridge segments. However, crustal thickness variations are sensitive to transform fault geometry and assumptions made about the pooled melt region. For example, if melt migration is not permitted across the transform fault, the calculated crustal thickness of the ITSC is approximately 5 km less than the crustal thicknesses predicted at the adjacent ridge segments. We apply these modeling techniques to Siqueiros transform fault and make direct comparisons between predicted crustal thickness and melt composition with gravity-derived crustal thickness variations and major element analyses of glass samples recovered from the Siqueiros transform fault domain.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1037 Magma genesis and partial melting (3619)
DE: 3010 Gravity and isostasy (1218, 1222)
DE: 3035 Midocean ridge processes
DE: 3039 Oceanic transform and fracture zone processes
SC: Tectonophysics [T]
MN: 2007 Fall Meeting