HR: 1330h
AN: B12A-0741    [PDF]
TI: Crustal Seismic Structure along the East Pacific Rise 8$\deg$20'N to 10$\deg$10'N: Crustal melt accumulation and its relation to Mantle Melt Delivery, Tectonic Segmentation, Seafloor Geology and Hydrothermal Activity
AU: * Christopher, L M
EM: lchristo@morgan.edu
AF: Morgan State University, Dept of Physics, Baltimore, MD 21251 United States
AU: Dunn, R
EM: dunnr@hawaii.edu
AF: University of Hawaii, Dept of Geology and Geophysics, Honolulu, HI 96822 United States
AU: Toomey, D
EM: drt@newberry.uoregon.edu
AF: University of Oregon, Dept of Geological Sciences, Eugene, OR 97403 United States
AU: Wilcock, W
EM: wilcock@uwashington.edu
AF: University of Washington, School of Oceanography, Seattle, WA 98195 United States
AU: Detrick, R
EM: rdetrick@whoi.edu
AF: WHOI, Dept of Geology and Geophysics, Woods Hole, MA 02543 United States
AB: The UNDERSHOOT seismic experiment was designed to test competing magma supply models for the East Pacific Rise (EPR). P-wave energy that traverses the ridge within the crust allows us to map the variability of magma storage within the crust along the entire length of the transform-bounded segment of the EPR between the Siqueiros and Clipperton fracture zones. This 200-km-long section of ridge exhibits several small discontinuities of the bathymetric structure and one large overlapping spreading center (OSC) at 9$\deg$03'N. Earlier work has shown that the ridge is underlain by a shallow melt lens at approximately 1.5 km depth and by a prominent low velocity zone (4-8 km wide) that extends from the melt lens downwards into the mantle. This low velocity zone is indicative of high temperatures and a partially molten region of up to 10-40 percent magma storage. During the undershoot experiment P-wave crustal refractions and Moho reflections uniformly sampled this low-velocity zone along the entire length of this transform-bounded ridge segment. We use this data to tomographically image variations of the low-velocity zone along the ridge, including crustal thickness variations, and by inference variations in magma storage and supply. We jointly solve for the three-dimensional velocity structure of the crust and crustal thickness using a newly developed tomographic technique. While vertical resolution is poor beneath the rise, the high density of crossing ray paths, over a wide range of angles, provides excellent constraints on lateral variations in velocity structure. Initial results of this study do not reveal a discontinuity in the crustal low-velocity region beneath the OSC as expected by some models of OSC formation. This result correlates with a mantle tomographic image [Dunn et al., 2001] which likewise does not reveal a discontinuity in the mantle level low-velocity region just beneath the OSC. Our results, in combination with tomographic images of the uppermost mantle, document relations between the distribution of crustal melt storage, mantle melt supply, and the characteristics of tectonic segmentation, the axial summit and active hydrothermal venting.
DE: 0902 Computational methods, seismic
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
SC: Biogeosciences [B]
MN: 2003 Fall Meeting