HR: 11:35h
AN: T32B-05    [Abstracts]
TI: Co-existing Overlapping-Spreading-Center and Ridge-Transform Geometry
AU: * Forsyth, D W
EM: Donald_Forsyth@brown.edu
AF: Department of Geological Sciences, Brown University, Providence, RI 02912, United States
AU: Kerber, L
EM: Laura_Kerber@brown.edu
AF: Department of Geological Sciences, Brown University, Providence, RI 02912, United States
AU: Pickle, R
EM: Robert_Pickle@brown.edu
AF: Department of Geological Sciences, Brown University, Providence, RI 02912, United States
AB: We have studied the plate boundary geometry and recent spreading history in the Quebrada-Discovery-Gofar fracture zone system on the East Pacific Rise at 3-4 °S using multi-beam bathymetry, side-scan sonar, magnetic anomalies, gravity anomalies, and seismicity. Each of the transforms has multiple segments separated by intratransform spreading centers. Collectively, the system currently has 8 active, intratransform centers ranging in length from about 5 to 70 km. Over the last 1 Ma, the geometry has evolved, including the death of two transform segments and the birth of another one. The Discovery transform is the most unusual. Although it has a well-defined bathymetric signature and is seismically active, another transform trace appears to have been recently abandoned and there is no clear, fossil fracture zone outside the active transform region. The current transform is rotated a few degrees counter- clockwise from the direction of plate motion. Unlike most East Pacific Rise ridge segments, the spreading center at the eastern terminus of the Discovery has an axial valley, rather than an axial high. We suggest that part of the Nazca-Pacific separation is taken up by dike intrusion and formation of grabens that extend beyond the nominal end of the spreading center at the western terminus of the Discovery transform and cut across pre-existing seafloor-spreading fabric, creating a form of overlapping spreading center. Another region of recent deformation lies between the eastern and western overlappers near the center of the transform, bounding an older, trapped block or microplate that has been rotated counterclockwise about 45 degrees. The current geometry appears to be a hybrid between a simple ridge-transform boundary and an overlapping spreading center.
DE: 7250 Transform faults
DE: 8155 Plate motions: general (3040)
DE: 8178 Tectonics and magmatism
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting